Decoding Microstructural Heterogeneity and Mechanical Anomalies in GMAW of AISI 1010 Steel through Multi-Technique Characterization

Decoding Microstructural Heterogeneity and Mechanical Anomalies in GMAW of AISI 1010 Steel through Multi-Technique Characterization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Decoding Microstructural Heterogeneity and Mechanical Anomalies in GMAW of AISI 1010 Steel through Multi-Technique Characterization MEHRAB RAHMAN This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6769543/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study explores the microstructural evolution and mechanical behavior of Gas Metal Arc Welded (GMAW) joints in AISI 1010 low-carbon steel to assess weld integrity and performance. A comprehensive evaluation combining optical microscopy, Rockwell B hardness profiling, Optical Emission Spectroscopy (OES), tensile testing, Charpy impact testing, and Scanning Electron Microscopy (SEM) was conducted. The weld zone (WZ) exhibited dendritic solidification and recorded the highest hardness, while the heat-affected zone (HAZ) showed a significant reduction due to thermal softening and grain coarsening. Tensile testing revealed a peak strength of 461.14 MPa, with fracture localized in the WZ, indicating it as the weakest region under axial loading despite its higher hardness. Face bend testing confirmed overall ductility, although surface cracking and delamination at the weld interface indicated incomplete fusion and internal discontinuities. SEM analysis revealed mixed-mode fracture behavior, including ductile dimples, cleavage planes, and intergranular tearing. Charpy impact testing at sub-zero temperatures further confirmed reduced fracture toughness in the fusion zone. These findings underscore that while GMAW can produce structurally sound joints in AISI 1010 steel, localized heterogeneities—particularly within the WZ—may compromise reliability. With optimized process control and defect monitoring, GMAW remains a viable and cost-effective welding solution for low-carbon steel structural applications. Gas metal arc welding MIG welding gas Fracture toughness Quenching Mild steel Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 1. Introduction Gas Metal Arc Welding (GMAW) is one of the most common welding processes used in modern manufacturing industries, especially for low-carbon steels. Due to high arc stability and deposition rate, it is suitable for automotive and structural applications [ 1 ]. For welding mild steels like AISI 1010, which has low carbon content and good weldability, careful control of thermal input is required to ensure structural integrity and desired mechanical properties [ 2 ]. The GMAW process produces three metallurgical regions in the weldment: base metal (BM), heat-affected zone (HAZ), and fusion zone (FZ). Each region has different thermal cycles and microstructural features that govern the local mechanical behavior. The BM has a ferrite-pearlite structure; the FZ solidifies from the molten pool and forms a dendritic microstructure influenced by cooling rates and alloying elements [ 3 ]. The HAZ is subjected to sub-solidus thermal exposure and experiences grain coarsening and phase transformations. It is divided into coarse-grained and fine-grained subzones based on proximity to the weld interface [ 4 ]. Understanding the chemical composition of the base metal and the MIG welding wire is essential to predicting weld performance, especially hardenability, phase transformation behavior, and defect susceptibility. This work applied AISI 1010 low-carbon steel as the base material, and the wire chosen was AWS ER70S-6. Their chemical composition is described in Tables 1 and 2 , which express the suitability of that welding for structural purposes. Table 1 Chemical Composition of AISI 1010 Steel Base Metal (OES Analysis) Elements Fe C Si Mn P S Cr Mo Ni Al Co Cu Mg V wt.% 98.3 0.13 0.21 1.16 0.01 0.0048 0.011 0.0032 0.0084 0.035 0.0031 0.0084 0.0013 0.0041 Elements Ti W Pb Sn B Ca Zr Zn Ba As N Se Sb Ta wt.% 0.0029 0.015 < 0.0050 0.0029 0.0004 < 0.0001 0.0045 0.0021 0.0054 0.0027 0.0183 0.0024 < 0.0010 0.0270 Table 2 Typical Chemical Composition of AWS ER70S-6 Welding Wire (wt.%) supplied by Tullyn International Co. Ltd. Elements C Mn Si P (max) S (max) Ni (max) Cr (max) Mo (max) V (max) Cu (max) wt.% 0.06–0.15 1.40–1.85 0.80–1.15 0.025 0.035 0.15 0.15 0.15 0.03 0.50 Higher amounts of Mn and Si in the filler wire improve arc stability and deoxidation, lower porosity, and improve the shape of the weld bead [ 5 ]. Due to the low carbon and trace alloying elements present in both materials, good fusion with low risk of cracking under normal welding conditions was achieved [ 6 ]. With optical microscopy, the analysis of microstructure can show grain morphology and the progress of phases through each weld zone. SEM is important for use, as it allows to study of fractures that occur at a microscopic level. With the help of SEM fractography, ductile aspects like micro-void coalescence, dimple lines can be spotted, as well as brittle aspects like cleavage facets and cracks between grains [ 7 ][ 8 ]. Numerous works have looked at GMAW in low-carbon steels, but it is also important to perform microstructure analysis, hardness mapping, standard mechanical testing (tensile, bend, impact), and failure analysis by SEM for a comprehensive understanding of welding behavior. In this work, butt joint of AISI 1010 mild steel made using GMAW and then investigated with the purpose of microstructural evolution, hardness and mechanical performance and dominant failure mechanisms by fractographic Analysis. Additionally, understanding the transformation kinetics in the HAZ and the associated tempering effects is critical for mild steels because excessive grain growth or carbide coarsening can lead to localized softening or embrittlement [ 9 ][ 10 ]. The variation in hardness across weld regions, especially the dip, is observed in the HAZ due to subcritical annealing, which has been a recurring concern in structural integrity assessments [ 11 ][ 12 ]. Moreover, the choice of shielding gas mixture (Ar–CO₂ blends) significantly influences bead shape, penetration depth, and cooling rates, which also govern metallurgical features, especially dendritic spacing, grain boundary oxidation, and residual stress development [ 13 ][ 14 ]. In this study, the weldability and mechanical performance of AISI 1010 low-carbon steel joints produced by the gas metal arc welding (GMAW) process were systematically investigated. Joints were prepared under monitored welding, and the results were examined to explore how base metal, HAZ, and weld metal respond to loading. I specifically aimed to link microstructural studies, which were done using OM and SEM, with certain tests conducted on samples, like tensile, hardness, bend, and impact testing. The review of this process shows that GMAW can reliably weld AISI 1010 steel and helps in choosing the best welding parameters for better results in industrial use. 2. Experimental procedures 2.1. Materials In this study, commercially available AISI 1010 low-carbon steel was used as the base material for its excellent weldability and various industrial uses. The material was obtained in hot-rolled condition, which had a thickness of 5.2 mm, and then sectioned into 97.5 mm x 37 mm specimens using an abrasive cutter. OES was employed to measure the chemical composition of AISI 1010 steel, and the results are shown in Table 1 . For the Gas Metal Arc Welding (GMAW) process, a copper-coated mild steel electrode wire conforming to AWS ER70S-6 specification was used. The electrode wire, supplied by Tullyn International Co. Ltd, had a nominal diameter of 1.0 mm. The typical chemical composition of the AWS ER70S-6 wire is provided in Table 2 [ 15 ]. A shielding gas mixture of 80% Argon and 20% Carbon Dioxide was used at a regulated flow rate of 15–20 L/min for protecting the weld pool and stabilizing the arc. All base materials and consumables were kept under dry conditions to prevent contamination or moisture pickup prior to welding. 2.2. Welding procedure The steel plates were cleaned thoroughly before welding using a wire brush to remove surface contaminants to ensure optimal arc stability and fusion. Direct Current Electrode Positive (DCEP) polarity was used to operate the welding setup, using an arc voltage of 20 V and a current of 100 A. ER70S-6 filler wire with a diameter of 1 mm was used, and a mixture of 80% Argon and 20% Carbon Dioxide was used as shielding gas, which was supplied at an optimized flow rate of approximately 15–20 L/min to prevent atmospheric contamination of the weld pool. The electrode wire was positioned carefully and fed into the torch, and fine-tuned shielding gas was flowed to maintain a stable arc. During welding, the torch was held at an angle of 15–20° from the vertical, and a straight weld bead was deposited by guiding the torch smoothly along the joint line. The wire feeding rate and travelling speed were controlled manually to ensure uniform heat input and consistent bead geometry. No backing plate or preheating was applied because the material's thickness permitted single-pass welding under ambient conditions. The trigger was released to stop wire feeding up to completion of the weld, and the workpiece was allowed to be quenched in water at room temperature (~ 25°C) to observe microstructural evolution and simulate rapid cooling conditions. A schematic illustration of the GMAW setup is provided in Fig. 1 for clarity. 2.3. Sample Geometry after welding: A 3D rendered model of the base plate with proper weld bead geometry was created using SolidWorks 2023, which is presented in Fig. 3. Besides, a 2D drawing with dimensional specifications is presented in Fig. 2 . They both provide a clear visualization of the weld joint configuration. 2.4. Testing and characterization 2.4.1. Chemical Composition Analysis Optical Emission Spectroscopy (OES) was used to determine the elemental composition of the base metal with a Foundry-Master Pro spectrometer. This technique enabled precise quantification of alloying elements to ensure the steel conformed to the AISI 1010 specification before welding. 2.4.2. Microstructural Examination An optical microscope (OM, Olympus GX51) was used to analyze the post-weld microstructure. Samples were extracted from the Coarsening Zone (CZ), Normalized Zone (NZ), Weld Zone (WZ), heat-affected zone (HAZ), and base metal (BM) of the welded sample. For analyzing in OM, Standard metallographic procedures were followed, including sectioning, grinding, polishing, and etching with 2% Nital. To observe phase transformations, grain size variations, and morphological differences induced by welding and subsequent water quenching, Micrographs were captured. 2.4.3. Hardness Testing The hardness distribution across the weldment was measured in the Rockwell B scale (HRB), following ASTM E18[ 16 ]. Indentations were taken at the center of the fusion zone, HAZ, and unaffected base metal to evaluate the hardness gradient and detect any localized hardening or softening due to thermal cycles and rapid quenching. 2.4.4. Mechanical Testing Transverse Tensile Test : Flat transverse tensile specimens were prepared as per ASTM E8M standards [ 17 ]. Testing was performed using a universal testing machine (UTM) at room temperature, and the ultimate tensile strength (UTS), yield strength (YS), and elongation were recorded. Face Bend Test: A B end test was performed to evaluate ductility and detect internal discontinuities according to AWS D1.1 guidelines[ 18 ]. The specimen was intended to undergo a 180° face bend with the weld region on the tensile side; however, the fracture initiated prematurely at an approximate bend angle of 100–120°. Impact Test : Charpy V-notch impact testing was conducted at room temperature following ASTM E23 [ 19 ]. The notch was positioned at the weld centerline to assess the joint’s toughness under dynamic loading. Impact energy absorption values were recorded and analyzed. 2.4.5. Fractographic Analysis using SEM The fracture surfaces of mechanically tested samples (transverse tensile, Charpy impact, and Nick Bend) were carefully sectioned and cleaned using acetone to remove surface contaminants. The SEM sample stubs were mounted using conductive carbon tape to ensure electrical grounding after drying in air. Before scanning, a thin layer of conductive gold coating was applied to the fracture surfaces using a sputter coater to avoid charging effects during SEM observation. The coated samples were then examined at 2000× magnification, which depends on the region of interest. To identify fracture features such as micro-voids, cleavage planes, intergranular tearing, and any other morphological characteristics indicative of ductile or brittle failure, special attention was given to key regions, including the fusion zone, heat-affected zone (HAZ), and unaffected base metal. All SEM imaging was performed under high-vacuum mode using a secondary electron detector. 3. Results and discussion 3.4. Metallographic Analysis of Welded Zones 3.4.1. Grain Size and Microstructural Observations Base Metal (BM): Table 3 Grain area of the BM using ImageJ Reading Area (mm²) Mean Min Max 1 1.321 165.659 43 237 2 1.203 164.567 40 211 3 1.824 175.567 42 223 4 1.198 168.504 39 214 5 1.094 151.024 42 168 6 1.265 151.507 48 205 7 0.958 161.440 40 198 8 1.135 145.665 40 210 9 2.035 124.858 48 197 10 1.464 150.208 38 198 Avg. 1.3968 — — — Heat-Affected Zone (HAZ): Table 4 Grain area of HAZ using ImageJ Reading Area (mm²) Mean Min Max 1 0.365 145.846 39 205 2 0.763 155.966 51 211 3 0.742 103.568 31 178 4 1.092 127.625 24 178 5 0.570 103.661 28 163 6 0.865 87.482 27 164 7 0.806 149.253 44 147 8 0.820 149.216 44 213 9 0.477 87.482 18 147 10 0.776 87.482 18 147 Avg. 0.7799 — — — Weld Zone (WZ): Table 5 Grain area of the WZ using ImageJ Reading Area (mm²) Mean Min Max 1 0.213 108.341 47 170 2 0.558 93.471 39 156 3 0.705 103.073 38 136 4 0.688 86.402 31 178 5 0.622 88.838 34 178 6 0.499 88.388 34 178 7 0.627 88.884 34 179 8 0.653 96.588 30 140 9 0.663 96.157 46 192 10 0.623 88.112 36 136 Avg. 0.5785 — — — Normalized Zone (NZ): Table 6 Grain area of the NZ using ImageJ Reading Area (mm²) Mean Min Max 1 1.255 126.196 37 177 2 0.824 126.197 47 200 3 1.200 123.697 32 183 4 0.764 103.073 38 186 5 0.869 124.053 34 178 6 0.467 86.323 34 178 7 0.651 123.928 20 163 8 0.597 98.588 25 165 9 0.101 76.958 23 154 10 0.162 111.861 41 169 Avg. 0.889 — — — Coarsening Zone (CZ): Table 7 Grain area of the CZ using ImageJ Reading Area (mm²) Mean Min Max 1 0.237 147.415 54 207 2 0.228 147.701 59 194 3 0.115 142.555 58 190 4 0.125 135.384 55 196 5 0.186 148.701 61 178 6 0.622 131.102 42 183 7 0.309 101.008 42 199 8 0.305 142.532 44 189 9 0.231 116.757 42 188 10 0.038 111.675 49 180 Avg. 0.2015 — — — Grain size and microstructural evolution were investigated across distinct regions of the metal inert gas (MIG)-welded mild steel butt joint. For my study, I focused on the base metal (BM), heat-affected zone (HAZ), weld zone (WZ), normalized zone (NZ), and coarsening zone (CZ). Due to localized thermal gradients and phase transformations induced during the welding cycle and subsequent cooling, variations in grain morphology were observed. The base metal exhibited the largest average grain area (1.3968 µm²), reflecting a rolled microstructure that remained unaffected by the thermal cycle. This morphology is consistent with prior studies indicating that hot-rolled steel retains equiaxed ferrite–pearlite grains in the absence of re-austenitization [ 20 ]. The HAZ showed a moderate grain size reduction (0.7799 µm²), a consequence of elevated thermal exposure that promoted partial grain growth without reaching the melting threshold. Such microstructural evolution corresponds closely with the typical transformation behavior reported in the subcritical HAZ of low-carbon steels [ 21 ]. The weld zone (WZ), having undergone full melting and rapid solidification, exhibited the finest average grain size (0.5785 µm²). This refinement is attributed to post-weld water quenching, which induced a rapid cooling rate and suppressed grain growth. The WZ showed that martensite is easily spotted after nital etching using an optical microscope because of its contrast appears dark. This phase results from the diffusionless transformation of austenite during rapid quenching, producing a body-centered tetragonal (BCT) structure known to significantly enhance hardness by impeding dislocation motion through lattice distortion caused by interstitial carbon atoms [ 22 ][ 23 ]. In the normalized zone (NZ), which is adjacent to the HAZ, the average area of grains increased slightly (0.8886 µm²). This structure reflects partial recrystallization under a controlled thermal regime, where retained austenite transformed into a fine ferrite–pearlite mix during relatively slow cooling. In this part of the specimen, the microstructure favors improved toughness and ductility while reducing the risk of brittle fracture [ 24 ]. Interestingly, the smallest average grain size (0.2015 µm²) was recorded in the coarsening zone (CZ), located at the HAZ–WZ interface. This counterintuitive grain refinement may be attributed to severe thermal cycling and steep thermal gradients that activate dynamic recrystallization mechanisms, suppressing conventional grain coarsening typically associated with this region [ 25 ]. Structural features of the grain also indicated how the sample was processed. The observation of equiaxed, rounded grains in the BM indicates that the steel was rolled at elevated temperatures, since recrystallization removes any anisotropy present in its grains [ 20 ]. In contrast, cold rolling usually causes grains in ferrite to become elongated and line up with the rolls [ 26 ]. These features confirm that the initial BM was hot-rolled before welding. 3.4.2. Grain Size–Hardness Interdependence Across the Weldment Microstructure To quantitatively evaluate grain refinement across the distinct regions of the welded mild steel joint, the ASTM grain size number (G) was determined by ASTM E112 [ 27 ] using the Planimetric method [ 28 ]. Grain counts were performed within a defined test area at 100× magnification, and the results were extrapolated to the standard grains per square inch at 100×. The relationship between the ASTM grain size number (G) and the number of grains per square inch at 100× magnification (N) is defined by: $$\:\text{G}=\frac{{\text{log}}_{10}\text{N}}{{\text{log}}_{10}2}+1$$ Table 8 ASTM grain numbers for each weld region Zone Area (µm²) Area (in²) Number of Grains Grains/Sq. Inch (500X) Grains/Sq. Inch (100X) ASTM Grain Number Base Metal (BM) 14.711 2.2802096 × 10⁻⁸ 11 482,411,792 12,060,294,800 34.4 ≈ 34 Heat Affected Zone (HAZ) 35.699 5.5333561 × 10⁻⁸ 27 487,949,367 12,198,734,175 34.5 ≈ 35 Weld Zone (WZ) 5.686 8.813318 × 10⁻⁹ 6 680,787,871 17,019,696,775 34.9 ≈ 35 Through the interplay between microstructural refinement and hardness distribution across the weldment, the underlying mechanisms governing the mechanical behavior of the MIG-welded mild steel joint were revealed. Demonstrating that reduced grain sizes impede dislocation motion and enhance strength, grain size analysis revealed a negative correlation with hardness, which aligns with the Hall–Petch effect [ 29 ][ 30 ]. The weld zone (WZ) exhibited the finest average grain area (0.5785 µm²) and the highest ASTM grain number (34.9 ≈ 35) among the evaluated zones, aligning with the maximum hardness value recorded at 65.7 HRB (Tables 8 and 9 ). This is attributed to rapid thermal cooling and subsequent solid-state phase transformation following fusion, which results in martensite formation that significantly improves strength and hardness[ 31 ][ 32 ]. Although the heat-affected zone (HAZ) exhibited a comparable ASTM grain number (34.5 ≈ 35), its average hardness was lower, with a minimum value of 64.8 HRB. This outcome is attributed to differences in phase morphology and residual stress state, rather than grain size alone[ 33 ] [ 34 ]. While the HAZ grain size was refined due to subcritical thermal exposure and partial recrystallization, the absence of martensite and the possible presence of softened or over-tempered ferrite–pearlite structures reduced the zone’s resistance to indentation [ 35 ]. Thus, despite similar ASTM numbers, the mechanical response diverges due to microstructural phase evolution and thermal history. The base metal (BM), in contrast, exhibited the coarsest grains (average 1.3968 µm², ASTM ~ 34), a nearly uniform hardness profile (65.1–65.4 HRB), and retained its hot-rolled ferrite–pearlite morphology, reflecting the absence of thermal cycling. These findings, collectively, highlight that hardness is influenced not only by grain size as a major contributor but also critically by the resulting phase constituents and post-solidification transformations [ 36 ]. Thus, the integrated evaluation of ASTM grain size and hardness provides a comprehensive understanding of weld zone performance, which also informs optimization strategies for weld quality and structural reliability. Table 9 Hardness measurements Zone Distance from Center (mm) Hardness (HRB) BM -30 65.3 BM -20 65.4 HAZ -2.5 65.2 WZ 0 65.7 HAZ 2.5 64.8 BM 20 65.1 BM 30 65.3 3.5. Weldability Assessment To evaluate the weldability of the investigated mild steel specimen, elemental composition was determined using Optical Emission Spectrometry (OES), as illustrated in Table 1 . The quantified average composition of key alloying elements was as follows: carbon (C) = 0.13%, manganese (Mn) = 1.16%, silicon (Si) = 0.213%, chromium (Cr) = 0.0111%, molybdenum (Mo) = 0.0032%, vanadium (V) = 0.041%, nickel (Ni) = 0.0085%, and copper (Cu) = 0.0084%. These elements significantly influence the hardness and weldability of steels and are thus incorporated into empirical carbon equivalent (CE) formulas [ 37 ]. Using these values, the Carbon Equivalent (CE) was calculated according to the International Institute for Welding (IIW) recognized empirical formula [ 38 ][ 39 ]: $$\:\text{C}\text{E}\:=\text{C}+\frac{\text{M}\text{n}+\text{S}\text{i}}{6}+\frac{\text{C}\text{r}+\text{M}\text{o}+\text{V}}{5}+\frac{\text{N}\text{i}+\text{C}\text{u}}{15}$$ Substituting the measured values into the equation yielded a CE of 0.371, which indicates favorable welding characteristics. Steels with CE ≤ 0.35 exhibit excellent weldability; 0.36 ≤ CE ≤ 0.40 corresponds to very good weldability; 0.41 ≤ CE ≤ 0.45 implies good weldability; and CE values exceeding 0.50 indicate poor weldability according to weldability classifications [ 38 ]. With a CE value of 0.371, the mild steel specimen falls within the "very good weldability" range, which confirms its suitability for structural applications where reliable fusion welding is required without the risk of excessive hardness or cracking in the heat-affected zone. 3.6. Mechanical properties A series of standardized mechanical tests were conducted to evaluate the mechanical integrity of the welded joint. Each test is presented along with its corresponding fractographic evaluation. 3.6.1. Transverse Tensile Test and Fractographic Analysis A transverse tensile test was performed on a butt-welded mild steel specimen to evaluate its ultimate tensile strength (UTS) and failure behavior. With a gauge length of 200 mm, a width of 25 mm, and a thickness of 8 mm, the specimen exhibited a measured tensile strength of 461.14 MPa. The fracture occurred at the center of the welded joint, which indicates that the weakest region was the weld zone under tensile loading. The resulting fracture surface was examined using Scanning Electron Microscopy (SEM) at a magnification of 2000× and an accelerating voltage of 20 kV. The SEM micrograph of the fracture surface is shown in Fig. 12 . The surface is predominantly populated by uniformly distributed, equiaxed dimples, reflecting a ductile fracture mechanism. These dimples arise from micro-void nucleation, growth, and coalescence under tensile loading [ 40 ]. Furthermore, tear ridges—elongated features observed between adjacent dimples—appear, providing further evidence of significant plastic deformation before the final fracture [ 41 ]. The characteristics observed in ductile metals that experience tensile overload failure indicate that the material underwent significant strain localization before it ultimately fractured [ 42 ]. The fracture morphology confirms the ductile rupture mechanism, and the joint demonstrated effective energy absorption when subjected to tensile loading. 3.6.2. Face Bend Test and Fractographic Analysis As shown in Fig. 13, after the test, a complete separation along the face of the weld zone occurred, and then the fracture surface was taken for further analysis. The specimen experienced a significant degree of bending; however, evident surface cracking and delamination at the weld zone were observed. These discontinuities indicate a lack of complete fusion and potential internal defects such as slag inclusions or porosity. The failure along the weld line suggests an inadequate weld during the welding process, which compromised joint integrity under bending stress. For investigating the fracture mechanism, Scanning Electron Microscopy (SEM) was employed on the fractured surface of one of the separated halves. Figure 14 shows the SEM image, which is captured at a magnification of 2000×. The fractographic analysis provides some interesting microstructural features that are usually linked to plastic deformation and ductile failure. On the fracture plane, I noticed several internal discontinuities, including clusters of micro-voids, elongated cavities, and areas of micro-shrinkage. These characteristics point to the processes of void nucleation, growth, and coalescence happening, which confirms that failure occurred by ductile fracture mode [ 43 ]. To make sure that welded joints are structurally sound, especially in load-bearing situations, it's crucial to achieve top-notch weld integrity, mechanical strength, and ductility. The failure observed during the face bend test, which showed cracking and delamination along the weld face, highlights the need for optimizing the welding process. 3.6.3. Impact Test and Fractographic Analysis To assess how sensitive the welded joint is to notches and its resistance to dynamic fractures, I conducted a Charpy V-notch impact test following ASTM E23[ 19 ] on a 1010 steel sample, which consisted of a GMAW weld. I made sure to place the notch right in the center of the weld zone (see Fig. 15). The impact test specimens were measured at 9 mm wide (with a few tweaks for the V-notch) and 6 mm thick, fitting snugly within the standard geometric guidelines [ 19 ]. Before diving into the testing, I conditioned the specimen in dry ice to mimic low-temperature service conditions. This step made the material more brittle, allowing us to get a better understanding of how well the weld could withstand fractures. The results showed it could absorb an impact energy of 14 J, with fractures occurring at the weld zone, which turned out to be the weakest point during sudden impacts. This behavior can be traced back to variations in the microstructure and possible stress points in the fusion zone, stemming from thermal cycling and solidification [ 44 ]. A closer inspection of the fractured surfaces showed a clean break, with no noticeable macroscopic defects like cracks, voids, or inclusions, suggesting that the overall weld quality was quite solid. I utilized Scanning Electron Microscopy (SEM) to investigate the fracture mechanism thoroughly. Observing the fracture surface at a magnification of 2000× and an accelerating voltage of 20 kV, I found evidence of mixed-mode failure, including cleavage steps, dimples, and a transition zone (Fig. 16 ). The cleavage facets suggest that a brittle fracture has occurred due to cleavage propagation, while the dimples indicate localized plastic deformation resulting from the merging of micro-voids [ 45 ][ 46 ]. The transition zone between these two areas showcases the complex stress state and metallurgical structure of the weld metal when it faces impact loading [ 47 ]. 4. Conclusion In this study, AISI 1010 low-carbon steel was welded using the Gas Metal Arc Welding (GMAW) technique, and a comprehensive analysis of microstructural features and mechanical performance was carried out. The following conclusions can be drawn from the investigation: Mild steel joints were successfully fabricated using the GMAW process with a single pass and no preheating. Full and defect-free penetration was achieved using ER70S-6 filler wire under controlled parameters, and the resulting bead geometry was uniform and sound. The fusion zone (WZ) exhibited a fine-grained dendritic structure due to quenching, while the heat-affected zone (HAZ) presented varied microstructural transformations, including coarse and fine subzones. Notably, the formation of martensite in the fusion zone due to water quenching contributed to increased hardness. Mechanical testing revealed that while the welded joints exhibited adequate tensile strength and ductility, fractures consistently occurred at the center of the weld during tensile loading, indicating that the fusion zone was the weakest region. The face bend test showed significant bending deformation; however, surface cracking and delamination were evident along the weld line. These observations suggest the presence of incomplete fusion and potential internal defects such as slag inclusions or porosity, which compromised the joint's structural integrity under bending stress. Despite these discontinuities, the Charpy impact test results demonstrated moderate energy absorption capacity, suggesting that the welded joint retains a degree of toughness, albeit with localized weaknesses. SEM fractography revealed a combination of ductile and brittle fracture features across different test zones. Ductile dimples, intergranular tearing, and cleavage facets indicated complex failure mechanisms governed by thermal history and local microstructural variations. Overall, the GMAW process was found to be effective for welding AISI 1010 steel, yielding joints with balanced strength, hardness, and toughness. Future work may explore optimized welding parameters, such as arc voltage, current, and travel speed, on fusion quality and defect minimization. Additionally, employing preheating, multi-pass welding techniques, or post-weld heat treatments (PWHT) may improve weld integrity by reducing residual stresses and promoting more homogeneous microstructures. Such approaches can contribute to enhancing both the strength and toughness of welded joints in structural applications. Declarations Funding The authors declare that no external funds or research grants were received for this study. Laboratory facilities were accessed with institutional support. Scanning Electron Microscopy (SEM) analysis was conducted with the author's personal funding. Competing Interests This work was initially carried out as part of an academic course project. Additional testing was conducted independently by the author using personal resources, without any external financial support, to enhance the quality and completeness of the study. The research was undertaken solely for academic development and to gain research experience. The author declares no financial interests or personal relationships that could have influenced the research. Author Contributions The author solely conceived and designed the study. Material preparation, data collection, experimental work, analysis, and interpretation were all carried out by the author. The manuscript was written and revised entirely by the author, who read and approved the final version. Acknowledgments The author gratefully acknowledges Professor Dr. H.M. Mamun Al Rashed and Lecturer Abrar Daiyan of the Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology (BUET), for their academic guidance and for facilitating access to laboratory resources throughout this investigation. Their support during the experimental phase and insightful instructions on the research methodology were invaluable. This work was conducted as part of an individual academic laboratory project without external funding; some experimental procedures were self-financed by the author. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6769543","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":466293328,"identity":"b6a01e46-248a-41d3-a8f5-481940eb1344","order_by":0,"name":"MEHRAB RAHMAN","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYBACfmbGhgOJf/7JgTjMMFFmBjbcWiTbmxsPfGw4YAzTIkFQi8GZ480HZwItaiBaC8ONxIbDvDvupK+ddvgAc2GbTR0D++EHzAVluHUwzgBpOfMsd9vttATmmW1pEgw8aQbMM87h1sIsAdTCw8YM1JJjwMzbdhjosBwGIAO3FjaolnSz2/kfgCr/SzDwv8GvhYfnYMPBmW2HE8xugw0/IMEgQcAWCfbGhgMfzqQZAv1icHjGuWTJNolnIAZuLfaH2R9/SKiwkTe7nfzwcUGZHT8/P5iBWwsKOAD2HYwxCkbBKBgFo4B8AADXxlXbvzzaVQAAAABJRU5ErkJggg==","orcid":"","institution":"BUET: Bangladesh University of Engineering and Technology","correspondingAuthor":true,"prefix":"","firstName":"MEHRAB","middleName":"","lastName":"RAHMAN","suffix":""}],"badges":[],"createdAt":"2025-05-28 15:27:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6769543/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6769543/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85017576,"identity":"ae769d05-54a0-48dc-9b15-1943d24de724","added_by":"auto","created_at":"2025-06-20 03:25:48","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":43545,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of the Gas Metal Arc Welding (GMAW) process\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/fc8110c2f67849ece0dad3c0.png"},{"id":85016466,"identity":"eb75c0c0-a32d-4396-9408-b23a1e71fd4e","added_by":"auto","created_at":"2025-06-20 03:17:42","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":42592,"visible":true,"origin":"","legend":"\u003cp\u003e2D drawing of the MIG welded sample showing joint geometry and dimensions.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/b1b813e715142f41681192a6.jpg"},{"id":85016480,"identity":"6cdad977-44ea-4523-8276-48da046c77d7","added_by":"auto","created_at":"2025-06-20 03:17:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":161343,"visible":true,"origin":"","legend":"\u003cp\u003eSolidWorks 3D Model of the Welded Specimen. (a) Front view (b) Isometric view (c) Top view (d) Side view\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/13606416a6e63345eab15ddf.png"},{"id":85016611,"identity":"a8563f7b-cdc8-4c54-a723-58a1c0270d17","added_by":"auto","created_at":"2025-06-20 03:17:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":639233,"visible":true,"origin":"","legend":"\u003cp\u003eMacrostructure \u0026amp; Microstructure of the welded sample in various regions\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/a277360fb2c5bccc30ea0330.png"},{"id":85016549,"identity":"cf4bffba-42ad-46e4-ac45-1b1b6b7b403e","added_by":"auto","created_at":"2025-06-20 03:17:46","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":162717,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Unaffected Base Metal (BM) (500X)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/45dbaa039afb495557a961d4.png"},{"id":85017696,"identity":"13a19f35-d3fc-4577-93a1-4a5ffd3361e7","added_by":"auto","created_at":"2025-06-20 03:33:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":136986,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Heat Affected Zone (HAZ) (500X)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/c9c78e4a645fd3a00994352c.png"},{"id":85016569,"identity":"930cbc88-50ce-4718-8862-ea46096d0a37","added_by":"auto","created_at":"2025-06-20 03:17:47","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":131603,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Weld Zone (WZ) (500X)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/f19043e03318ed7c586e89e3.png"},{"id":85016531,"identity":"3cff3b17-12c2-4c5d-998d-389ab02a771d","added_by":"auto","created_at":"2025-06-20 03:17:45","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":140379,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Normalized Zone (NZ) (500X)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/386d2600c4af24ff61abffba.png"},{"id":85016511,"identity":"1a8c5940-9e2a-474c-a00c-48f82b7fb821","added_by":"auto","created_at":"2025-06-20 03:17:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":136285,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Coarsening Zone (CZ) (500X)\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/29725c5c8bcd7bf41cb3d427.png"},{"id":85016562,"identity":"35472e56-153b-4d31-bc26-048ac617d931","added_by":"auto","created_at":"2025-06-20 03:17:47","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":8261,"visible":true,"origin":"","legend":"\u003cp\u003eHardness Profile\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/1a0cbafcd9811cf931fad516.jpg"},{"id":85016651,"identity":"764d6b50-ca25-4283-a14d-e128d5978025","added_by":"auto","created_at":"2025-06-20 03:17:51","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":141754,"visible":true,"origin":"","legend":"\u003cp\u003eTransverse tensile test (a)Before and (b)After the test\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/203cdda77262ea4ac2142d86.png"},{"id":85016461,"identity":"58dde4a9-18cc-44ab-8eb2-66781b9bdc4e","added_by":"auto","created_at":"2025-06-20 03:17:41","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":92609,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of the Tensile fractured surface of welded material\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/e6fbdf5cdb84e55730ad2a02.png"},{"id":85016468,"identity":"21fee9b7-9c57-4846-9e6d-4e42cc1b4a25","added_by":"auto","created_at":"2025-06-20 03:17:42","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":231388,"visible":true,"origin":"","legend":"\u003cp\u003eAfter the face bend test (a) just after the test (b) after breaking\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/b646d3859eb1deec645ada79.png"},{"id":85017571,"identity":"2c03db36-3292-4e8d-b074-78a054a37959","added_by":"auto","created_at":"2025-06-20 03:25:47","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":91234,"visible":true,"origin":"","legend":"\u003cp\u003eFractographic Evaluation using SEM After Face Bend Test\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/135b378c1d5a16b73596f9ec.png"},{"id":85016540,"identity":"4b95757b-7dcd-41df-bd38-be4c130f2e1b","added_by":"auto","created_at":"2025-06-20 03:17:46","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":89411,"visible":true,"origin":"","legend":"\u003cp\u003eImpact test of V-notched sample (a) before and (b) after the test\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/687fbf10d468a2d7eea16cc5.png"},{"id":85016463,"identity":"faece483-4f18-4160-b6d1-ee48fe98ddd0","added_by":"auto","created_at":"2025-06-20 03:17:41","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":387407,"visible":true,"origin":"","legend":"\u003cp\u003eFractographic Evaluation using SEM after Impact Test at dry ice condition\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/de3961938e853aaa2ea85249.png"},{"id":87089557,"identity":"f6bb3b73-1148-473b-a6f3-d2d45c21e7dd","added_by":"auto","created_at":"2025-07-19 07:55:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3851830,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/55a701e3-fcad-4e2d-9275-e32e4fdb79c5.pdf"},{"id":85016457,"identity":"e330c02c-cd83-44ee-9449-b6576d244465","added_by":"auto","created_at":"2025-06-20 03:17:41","extension":"sldprt","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":80971,"visible":true,"origin":"","legend":"","description":"","filename":"3DRender.sldprt","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/27b7f81c503ce4f6a0915d6c.sldprt"},{"id":85016554,"identity":"90ae987c-17df-4c6e-93b5-0eef53e1eaff","added_by":"auto","created_at":"2025-06-20 03:17:47","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":21506,"visible":true,"origin":"","legend":"","description":"","filename":"declarationofcompetinginterests.docx","url":"https://assets-eu.researchsquare.com/files/rs-6769543/v1/d2f425670b2bc0c9e685dd42.docx"}],"financialInterests":"","formattedTitle":"Decoding Microstructural Heterogeneity and Mechanical Anomalies in GMAW of AISI 1010 Steel through Multi-Technique Characterization","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGas Metal Arc Welding (GMAW) is one of the most common welding processes used in modern manufacturing industries, especially for low-carbon steels. Due to high arc stability and deposition rate, it is suitable for automotive and structural applications [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. For welding mild steels like AISI 1010, which has low carbon content and good weldability, careful control of thermal input is required to ensure structural integrity and desired mechanical properties [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe GMAW process produces three metallurgical regions in the weldment: base metal (BM), heat-affected zone (HAZ), and fusion zone (FZ). Each region has different thermal cycles and microstructural features that govern the local mechanical behavior. The BM has a ferrite-pearlite structure; the FZ solidifies from the molten pool and forms a dendritic microstructure influenced by cooling rates and alloying elements [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The HAZ is subjected to sub-solidus thermal exposure and experiences grain coarsening and phase transformations. It is divided into coarse-grained and fine-grained subzones based on proximity to the weld interface [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eUnderstanding the chemical composition of the base metal and the MIG welding wire is essential to predicting weld performance, especially hardenability, phase transformation behavior, and defect susceptibility. This work applied AISI 1010 low-carbon steel as the base material, and the wire chosen was AWS ER70S-6. Their chemical composition is described in Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, which express the suitability of that welding for structural purposes.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical Composition of AISI 1010 Steel Base Metal (OES Analysis)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"15\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv 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align=\"left\" colname=\"c10\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eCo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c14\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c15\"\u003e \u003cp\u003eV\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ewt.%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e98.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.0048\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.011\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0032\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.0084\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0031\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e0.0084\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e0.0013\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e0.0041\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eW\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eZr\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eBa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eAs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eSe\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003eSb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003eTa\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ewt.%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0004\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.0045\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.0054\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.0027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0183\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e0.0024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e0.0270\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTypical Chemical Composition of AWS ER70S-6 Welding Wire (wt.%) supplied by Tullyn International Co. Ltd.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElements\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eS (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNi (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCr (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMo (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eV (max)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eCu (max)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ewt.%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.06\u0026ndash;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.40\u0026ndash;1.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.80\u0026ndash;1.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eHigher amounts of Mn and Si in the filler wire improve arc stability and deoxidation, lower porosity, and improve the shape of the weld bead [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Due to the low carbon and trace alloying elements present in both materials, good fusion with low risk of cracking under normal welding conditions was achieved [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWith optical microscopy, the analysis of microstructure can show grain morphology and the progress of phases through each weld zone. SEM is important for use, as it allows to study of fractures that occur at a microscopic level. With the help of SEM fractography, ductile aspects like micro-void coalescence, dimple lines can be spotted, as well as brittle aspects like cleavage facets and cracks between grains [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e][\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Numerous works have looked at GMAW in low-carbon steels, but it is also important to perform microstructure analysis, hardness mapping, standard mechanical testing (tensile, bend, impact), and failure analysis by SEM for a comprehensive understanding of welding behavior. In this work, butt joint of AISI 1010 mild steel made using GMAW and then investigated with the purpose of microstructural evolution, hardness and mechanical performance and dominant failure mechanisms by fractographic Analysis.\u003c/p\u003e \u003cp\u003eAdditionally, understanding the transformation kinetics in the HAZ and the associated tempering effects is critical for mild steels because excessive grain growth or carbide coarsening can lead to localized softening or embrittlement [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e][\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The variation in hardness across weld regions, especially the dip, is observed in the HAZ due to subcritical annealing, which has been a recurring concern in structural integrity assessments [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e][\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Moreover, the choice of shielding gas mixture (Ar\u0026ndash;CO₂ blends) significantly influences bead shape, penetration depth, and cooling rates, which also govern metallurgical features, especially dendritic spacing, grain boundary oxidation, and residual stress development [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e][\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, the weldability and mechanical performance of AISI 1010 low-carbon steel joints produced by the gas metal arc welding (GMAW) process were systematically investigated. Joints were prepared under monitored welding, and the results were examined to explore how base metal, HAZ, and weld metal respond to loading. I specifically aimed to link microstructural studies, which were done using OM and SEM, with certain tests conducted on samples, like tensile, hardness, bend, and impact testing. The review of this process shows that GMAW can reliably weld AISI 1010 steel and helps in choosing the best welding parameters for better results in industrial use.\u003c/p\u003e"},{"header":"2. Experimental procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Materials\u003c/h2\u003e\n\u003cp\u003eIn this study, commercially available AISI 1010 low-carbon steel was used as the base material for its excellent weldability and various industrial uses. The material was obtained in hot-rolled condition, which had a thickness of 5.2 mm, and then sectioned into 97.5 mm x 37 mm specimens using an abrasive cutter. OES was employed to measure the chemical composition of AISI 1010 steel, and the results are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eFor the Gas Metal Arc Welding (GMAW) process, a copper-coated mild steel electrode wire conforming to AWS ER70S-6 specification was used. The electrode wire, supplied by Tullyn International Co. Ltd, had a nominal diameter of 1.0 mm. The typical chemical composition of the AWS ER70S-6 wire is provided in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eA shielding gas mixture of 80% Argon and 20% Carbon Dioxide was used at a regulated flow rate of 15\u0026ndash;20 L/min for protecting the weld pool and stabilizing the arc. All base materials and consumables were kept under dry conditions to prevent contamination or moisture pickup prior to welding.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Welding procedure\u003c/h2\u003e\n\u003cp\u003eThe steel plates were cleaned thoroughly before welding using a wire brush to remove surface contaminants to ensure optimal arc stability and fusion. Direct Current Electrode Positive (DCEP) polarity was used to operate the welding setup, using an arc voltage of 20 V and a current of 100 A. ER70S-6 filler wire with a diameter of 1 mm was used, and a mixture of 80% Argon and 20% Carbon Dioxide was used as shielding gas, which was supplied at an optimized flow rate of approximately 15\u0026ndash;20 L/min to prevent atmospheric contamination of the weld pool. The electrode wire was positioned carefully and fed into the torch, and fine-tuned shielding gas was flowed to maintain a stable arc. During welding, the torch was held at an angle of 15\u0026ndash;20\u0026deg; from the vertical, and a straight weld bead was deposited by guiding the torch smoothly along the joint line. The wire feeding rate and travelling speed were controlled manually to ensure uniform heat input and consistent bead geometry. No backing plate or preheating was applied because the material's thickness permitted single-pass welding under ambient conditions. The trigger was released to stop wire feeding up to completion of the weld, and the workpiece was allowed to be quenched in water at room temperature (~\u0026thinsp;25\u0026deg;C) to observe microstructural evolution and simulate rapid cooling conditions. A schematic illustration of the GMAW setup is provided in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e for clarity.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3. Sample Geometry after welding:\u003c/h2\u003e\n\u003cp\u003eA 3D rendered model of the base plate with proper weld bead geometry was created using SolidWorks 2023, which is presented in Fig.\u0026nbsp;3. Besides, a 2D drawing with dimensional specifications is presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. They both provide a clear visualization of the weld joint configuration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4. Testing and characterization\u003c/h2\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.1. Chemical Composition Analysis\u003c/h2\u003e\n\u003cp\u003eOptical Emission Spectroscopy (OES) was used to determine the elemental composition of the base metal with a Foundry-Master Pro spectrometer. This technique enabled precise quantification of alloying elements to ensure the steel conformed to the AISI 1010 specification before welding.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.2. Microstructural Examination\u003c/h2\u003e\n\u003cp\u003eAn optical microscope (OM, Olympus GX51) was used to analyze the post-weld microstructure. Samples were extracted from the Coarsening Zone (CZ), Normalized Zone (NZ), Weld Zone (WZ), heat-affected zone (HAZ), and base metal (BM) of the welded sample. For analyzing in OM, Standard metallographic procedures were followed, including sectioning, grinding, polishing, and etching with 2% Nital. To observe phase transformations, grain size variations, and morphological differences induced by welding and subsequent water quenching, Micrographs were captured.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.3. Hardness Testing\u003c/h2\u003e\n\u003cp\u003eThe hardness distribution across the weldment was measured in the Rockwell B scale (HRB), following ASTM E18[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Indentations were taken at the center of the fusion zone, HAZ, and unaffected base metal to evaluate the hardness gradient and detect any localized hardening or softening due to thermal cycles and rapid quenching.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.4. Mechanical Testing\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cem\u003eTransverse Tensile Test\u003c/em\u003e: Flat transverse tensile specimens were prepared as per ASTM E8M standards [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]. Testing was performed using a universal testing machine (UTM) at room temperature, and the ultimate tensile strength (UTS), yield strength (YS), and elongation were recorded.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cem\u003eFace Bend Test: A B\u003c/em\u003eend test was performed to evaluate ductility and detect internal discontinuities according to AWS D1.1 guidelines[\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. The specimen was intended to undergo a 180\u0026deg; face bend with the weld region on the tensile side; however, the fracture initiated prematurely at an approximate bend angle of 100\u0026ndash;120\u0026deg;.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003e\u003cem\u003eImpact Test\u003c/em\u003e: Charpy V-notch impact testing was conducted at room temperature following ASTM E23 [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. The notch was positioned at the weld centerline to assess the joint\u0026rsquo;s toughness under dynamic loading. Impact energy absorption values were recorded and analyzed.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n\u003ch2\u003e2.4.5. Fractographic Analysis using SEM\u003c/h2\u003e\n\u003cp\u003eThe fracture surfaces of mechanically tested samples (transverse tensile, Charpy impact, and Nick Bend) were carefully sectioned and cleaned using acetone to remove surface contaminants. The SEM sample stubs were mounted using conductive carbon tape to ensure electrical grounding after drying in air. Before scanning, a thin layer of conductive gold coating was applied to the fracture surfaces using a sputter coater to avoid charging effects during SEM observation. The coated samples were then examined at 2000\u0026times; magnification, which depends on the region of interest. To identify fracture features such as micro-voids, cleavage planes, intergranular tearing, and any other morphological characteristics indicative of ductile or brittle failure, special attention was given to key regions, including the fusion zone, heat-affected zone (HAZ), and unaffected base metal. All SEM imaging was performed under high-vacuum mode using a secondary electron detector.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4. Metallographic Analysis of Welded Zones\u003c/h2\u003e\n\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n\u003ch2\u003e3.4.1. Grain Size and Microstructural Observations\u0026nbsp;\u003c/h2\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\n\u003cul\u003e\n\u003cli\u003eBase Metal (BM):\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGrain area of the BM using ImageJ\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eReading\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (mm\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMin\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMax\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.321\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e165.659\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e43\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e237\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.203\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e164.567\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e211\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.824\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e175.567\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e223\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.198\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e168.504\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e214\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.094\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e151.024\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e168\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.265\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e151.507\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e205\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.958\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e161.440\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e198\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.135\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e145.665\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e40\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e210\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e2.035\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e124.858\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e48\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e197\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.464\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e150.208\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e198\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAvg.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.3968\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eHeat-Affected Zone (HAZ):\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGrain area of HAZ using ImageJ\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eReading\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (mm\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMin\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMax\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.365\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e145.846\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e205\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.763\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e155.966\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e51\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e211\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.742\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e103.568\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.092\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e127.625\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.570\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e103.661\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e163\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.865\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e87.482\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e164\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.806\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e149.253\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.820\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e149.216\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e213\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.477\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e87.482\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e18\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.776\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e87.482\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e18\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAvg.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.7799\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eWeld Zone (WZ):\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab5\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGrain area of the WZ using ImageJ\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eReading\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (mm\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMin\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMax\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.213\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e108.341\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e170\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.558\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e93.471\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e39\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e156\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.705\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e103.073\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e136\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.688\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e86.402\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e31\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.622\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.838\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.499\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.388\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.627\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.884\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e179\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.653\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e96.588\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e140\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.663\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e96.157\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e46\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e192\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.623\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.112\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e36\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e136\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAvg.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.5785\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003eNormalized Zone (NZ):\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab6\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGrain area of the NZ using ImageJ\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eReading\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (mm\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMin\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMax\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.255\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e126.196\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e37\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e177\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.824\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e126.197\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e47\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e200\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e1.200\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e123.697\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e32\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e183\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.764\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e103.073\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e186\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.869\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e124.053\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.467\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e86.323\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.651\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e123.928\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e163\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.597\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e98.588\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e165\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.101\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e76.958\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e154\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.162\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e111.861\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e41\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e169\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAvg.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.889\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\n\u003cul\u003e\n\u003cli\u003eCoarsening Zone (CZ): \u0026nbsp;\u0026nbsp;\u003c/li\u003e\n\u003c/ul\u003e\n\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab7\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eGrain area of the CZ using ImageJ\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eReading\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (mm\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMean\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMin\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMax\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.237\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147.415\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e54\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e207\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.228\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147.701\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e59\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e194\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.115\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e142.555\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e58\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e190\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.125\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e135.384\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e55\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e196\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.186\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e148.701\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e61\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e178\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.622\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e131.102\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e183\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.309\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e101.008\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e199\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.305\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e142.532\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e44\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e189\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.231\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e116.757\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e188\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.038\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e111.675\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e49\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e180\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAvg.\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.2015\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u0026mdash;\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eGrain size and microstructural evolution were investigated across distinct regions of the metal inert gas (MIG)-welded mild steel butt joint. For my study, I focused on the base metal (BM), heat-affected zone (HAZ), weld zone (WZ), normalized zone (NZ), and coarsening zone (CZ). Due to localized thermal gradients and phase transformations induced during the welding cycle and subsequent cooling, variations in grain morphology were observed.\u003c/p\u003e\n\u003cp\u003eThe base metal exhibited the largest average grain area (1.3968 \u0026micro;m\u0026sup2;), reflecting a rolled microstructure that remained unaffected by the thermal cycle. This morphology is consistent with prior studies indicating that hot-rolled steel retains equiaxed ferrite\u0026ndash;pearlite grains in the absence of re-austenitization [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe HAZ showed a moderate grain size reduction (0.7799 \u0026micro;m\u0026sup2;), a consequence of elevated thermal exposure that promoted partial grain growth without reaching the melting threshold. Such microstructural evolution corresponds closely with the typical transformation behavior reported in the subcritical HAZ of low-carbon steels [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe weld zone (WZ), having undergone full melting and rapid solidification, exhibited the finest average grain size (0.5785 \u0026micro;m\u0026sup2;). This refinement is attributed to post-weld water quenching, which induced a rapid cooling rate and suppressed grain growth. The WZ showed that martensite is easily spotted after nital etching using an optical microscope because of its contrast appears dark. This phase results from the diffusionless transformation of austenite during rapid quenching, producing a body-centered tetragonal (BCT) structure known to significantly enhance hardness by impeding dislocation motion through lattice distortion caused by interstitial carbon atoms [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eIn the normalized zone (NZ), which is adjacent to the HAZ, the average area of grains increased slightly (0.8886 \u0026micro;m\u0026sup2;). This structure reflects partial recrystallization under a controlled thermal regime, where retained austenite transformed into a fine ferrite\u0026ndash;pearlite mix during relatively slow cooling. In this part of the specimen, the microstructure favors improved toughness and ductility while reducing the risk of brittle fracture [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eInterestingly, the smallest average grain size (0.2015 \u0026micro;m\u0026sup2;) was recorded in the coarsening zone (CZ), located at the HAZ\u0026ndash;WZ interface. This counterintuitive grain refinement may be attributed to severe thermal cycling and steep thermal gradients that activate dynamic recrystallization mechanisms, suppressing conventional grain coarsening typically associated with this region [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eStructural features of the grain also indicated how the sample was processed. The observation of equiaxed, rounded grains in the BM indicates that the steel was rolled at elevated temperatures, since recrystallization removes any anisotropy present in its grains [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. In contrast, cold rolling usually causes grains in ferrite to become elongated and line up with the rolls [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. These features confirm that the initial BM was hot-rolled before welding.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n\u003ch2\u003e3.4.2. Grain Size\u0026ndash;Hardness Interdependence Across the Weldment Microstructure\u003c/h2\u003e\n\u003cp\u003eTo quantitatively evaluate grain refinement across the distinct regions of the welded mild steel joint, the ASTM grain size number (G) was determined by ASTM E112 [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e] using the Planimetric method [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. Grain counts were performed within a defined test area at 100\u0026times; magnification, and the results were extrapolated to the standard grains per square inch at 100\u0026times;.\u003c/p\u003e\n\u003cp\u003eThe relationship between the ASTM grain size number (G) and the number of grains per square inch at 100\u0026times; magnification (N) is defined by:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$$\\:\\text{G}=\\frac{{\\text{log}}_{10}\\text{N}}{{\\text{log}}_{10}2}+1$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab8\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eASTM grain numbers for each weld region\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eZone\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (\u0026micro;m\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eArea (in\u0026sup2;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eNumber of Grains\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eGrains/Sq. Inch (500X)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eGrains/Sq. Inch (100X)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eASTM Grain Number\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBase Metal (BM)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e14.711\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026times;\"\u003e\n\u003cp\u003e2.2802096 \u0026times; 10⁻⁸\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e11\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e482,411,792\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12,060,294,800\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.4\u0026thinsp;\u0026asymp;\u0026thinsp;34\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHeat Affected Zone (HAZ)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e35.699\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026times;\"\u003e\n\u003cp\u003e5.5333561 \u0026times; 10⁻⁸\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e27\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e487,949,367\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e12,198,734,175\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.5\u0026thinsp;\u0026asymp;\u0026thinsp;35\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWeld Zone (WZ)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e5.686\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\"\u0026times;\"\u003e\n\u003cp\u003e8.813318 \u0026times; 10⁻⁹\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e680,787,871\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e17,019,696,775\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e34.9\u0026thinsp;\u0026asymp;\u0026thinsp;35\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThrough the interplay between microstructural refinement and hardness distribution across the weldment, the underlying mechanisms governing the mechanical behavior of the MIG-welded mild steel joint were revealed. Demonstrating that reduced grain sizes impede dislocation motion and enhance strength, grain size analysis revealed a negative correlation with hardness, which aligns with the Hall\u0026ndash;Petch effect [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The weld zone (WZ) exhibited the finest average grain area (0.5785 \u0026micro;m\u0026sup2;) and the highest ASTM grain number (34.9\u0026thinsp;\u0026asymp;\u0026thinsp;35) among the evaluated zones, aligning with the maximum hardness value recorded at 65.7 HRB (Tables\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e). This is attributed to rapid thermal cooling and subsequent solid-state phase transformation following fusion, which results in martensite formation that significantly improves strength and hardness[\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. Although the heat-affected zone (HAZ) exhibited a comparable ASTM grain number (34.5\u0026thinsp;\u0026asymp;\u0026thinsp;35), its average hardness was lower, with a minimum value of 64.8 HRB. This outcome is attributed to differences in phase morphology and residual stress state, rather than grain size alone[\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e] [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. While the HAZ grain size was refined due to subcritical thermal exposure and partial recrystallization, the absence of martensite and the possible presence of softened or over-tempered ferrite\u0026ndash;pearlite structures reduced the zone\u0026rsquo;s resistance to indentation [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. Thus, despite similar ASTM numbers, the mechanical response diverges due to microstructural phase evolution and thermal history. The base metal (BM), in contrast, exhibited the coarsest grains (average 1.3968 \u0026micro;m\u0026sup2;, ASTM\u0026thinsp;~\u0026thinsp;34), a nearly uniform hardness profile (65.1\u0026ndash;65.4 HRB), and retained its hot-rolled ferrite\u0026ndash;pearlite morphology, reflecting the absence of thermal cycling. These findings, collectively, highlight that hardness is influenced not only by grain size as a major contributor but also critically by the resulting phase constituents and post-solidification transformations [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. Thus, the integrated evaluation of ASTM grain size and hardness provides a comprehensive understanding of weld zone performance, which also informs optimization strategies for weld quality and structural reliability.\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab10\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 9\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eHardness measurements\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eZone\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eDistance from Center (mm)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eHardness (HRB)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBM\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBM\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.4\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHAZ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e-2.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.2\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eWZ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.7\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHAZ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e64.8\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBM\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.1\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eBM\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e65.3\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n\u003ch2\u003e3.5. Weldability Assessment\u003c/h2\u003e\n\u003cp\u003eTo evaluate the weldability of the investigated mild steel specimen, elemental composition was determined using Optical Emission Spectrometry (OES), as illustrated in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The quantified average composition of key alloying elements was as follows: carbon (C)\u0026thinsp;=\u0026thinsp;0.13%, manganese (Mn)\u0026thinsp;=\u0026thinsp;1.16%, silicon (Si)\u0026thinsp;=\u0026thinsp;0.213%, chromium (Cr)\u0026thinsp;=\u0026thinsp;0.0111%, molybdenum (Mo)\u0026thinsp;=\u0026thinsp;0.0032%, vanadium (V)\u0026thinsp;=\u0026thinsp;0.041%, nickel (Ni)\u0026thinsp;=\u0026thinsp;0.0085%, and copper (Cu)\u0026thinsp;=\u0026thinsp;0.0084%. These elements significantly influence the hardness and weldability of steels and are thus incorporated into empirical carbon equivalent (CE) formulas [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eUsing these values, the Carbon Equivalent (CE) was calculated according to the International Institute for Welding (IIW) recognized empirical formula [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equb\" class=\"mathdisplay\"\u003e$$\\:\\text{C}\\text{E}\\:=\\text{C}+\\frac{\\text{M}\\text{n}+\\text{S}\\text{i}}{6}+\\frac{\\text{C}\\text{r}+\\text{M}\\text{o}+\\text{V}}{5}+\\frac{\\text{N}\\text{i}+\\text{C}\\text{u}}{15}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eSubstituting the measured values into the equation yielded a CE of 0.371, which indicates favorable welding characteristics. Steels with CE\u0026thinsp;\u0026le;\u0026thinsp;0.35 exhibit excellent weldability; 0.36\u0026thinsp;\u0026le;\u0026thinsp;CE\u0026thinsp;\u0026le;\u0026thinsp;0.40 corresponds to very good weldability; 0.41\u0026thinsp;\u0026le;\u0026thinsp;CE\u0026thinsp;\u0026le;\u0026thinsp;0.45 implies good weldability; and CE values exceeding 0.50 indicate poor weldability according to weldability classifications [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. With a CE value of 0.371, the mild steel specimen falls within the \"very good weldability\" range, which confirms its suitability for structural applications where reliable fusion welding is required without the risk of excessive hardness or cracking in the heat-affected zone.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n\u003ch2\u003e3.6. Mechanical properties\u003c/h2\u003e\n\u003cp\u003eA series of standardized mechanical tests were conducted to evaluate the mechanical integrity of the welded joint. Each test is presented along with its corresponding fractographic evaluation.\u003c/p\u003e\n\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n\u003ch2\u003e3.6.1. Transverse Tensile Test and Fractographic Analysis\u003c/h2\u003e\n\u003cp\u003eA transverse tensile test was performed on a butt-welded mild steel specimen to evaluate its ultimate tensile strength (UTS) and failure behavior.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWith a gauge length of 200 mm, a width of 25 mm, and a thickness of 8 mm, the specimen exhibited a measured tensile strength of 461.14 MPa. The fracture occurred at the center of the welded joint, which indicates that the weakest region was the weld zone under tensile loading.\u003c/p\u003e\n\u003cp\u003eThe resulting fracture surface was examined using Scanning Electron Microscopy (SEM) at a magnification of 2000\u0026times; and an accelerating voltage of 20 kV. The SEM micrograph of the fracture surface is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e12\u003c/span\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe surface is predominantly populated by uniformly distributed, equiaxed dimples, reflecting a ductile fracture mechanism. These dimples arise from micro-void nucleation, growth, and coalescence under tensile loading [\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]. Furthermore, tear ridges\u0026mdash;elongated features observed between adjacent dimples\u0026mdash;appear, providing further evidence of significant plastic deformation before the final fracture [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. The characteristics observed in ductile metals that experience tensile overload failure indicate that the material underwent significant strain localization before it ultimately fractured [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. The fracture morphology confirms the ductile rupture mechanism, and the joint demonstrated effective energy absorption when subjected to tensile loading.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n\u003ch2\u003e3.6.2. Face Bend Test and Fractographic Analysis\u003c/h2\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;13, after the test, a complete separation along the face of the weld zone occurred, and then the fracture surface was taken for further analysis.\u003c/p\u003e\n\u003cp\u003eThe specimen experienced a significant degree of bending; however, evident surface cracking and delamination at the weld zone were observed. These discontinuities indicate a lack of complete fusion and potential internal defects such as slag inclusions or porosity. The failure along the weld line suggests an inadequate weld during the welding process, which compromised joint integrity under bending stress. For investigating the fracture mechanism, Scanning Electron Microscopy (SEM) was employed on the fractured surface of one of the separated halves.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e14\u003c/span\u003e shows the SEM image, which is captured at a magnification of 2000\u0026times;. The fractographic analysis provides some interesting microstructural features that are usually linked to plastic deformation and ductile failure. On the fracture plane, I noticed several internal discontinuities, including clusters of micro-voids, elongated cavities, and areas of micro-shrinkage. These characteristics point to the processes of void nucleation, growth, and coalescence happening, which confirms that failure occurred by ductile fracture mode [\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e]. To make sure that welded joints are structurally sound, especially in load-bearing situations, it's crucial to achieve top-notch weld integrity, mechanical strength, and ductility. The failure observed during the face bend test, which showed cracking and delamination along the weld face, highlights the need for optimizing the welding process.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\n\u003ch2\u003e3.6.3. Impact Test and Fractographic Analysis\u003c/h2\u003e\n\u003cp\u003eTo assess how sensitive the welded joint is to notches and its resistance to dynamic fractures, I conducted a Charpy V-notch impact test following ASTM E23[\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e] on a 1010 steel sample, which consisted of a GMAW weld. I made sure to place the notch right in the center of the weld zone (see Fig.\u0026nbsp;15).\u003c/p\u003e\n\u003cp\u003eThe impact test specimens were measured at 9 mm wide (with a few tweaks for the V-notch) and 6 mm thick, fitting snugly within the standard geometric guidelines [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Before diving into the testing, I conditioned the specimen in dry ice to mimic low-temperature service conditions. This step made the material more brittle, allowing us to get a better understanding of how well the weld could withstand fractures. The results showed it could absorb an impact energy of 14 J, with fractures occurring at the weld zone, which turned out to be the weakest point during sudden impacts. This behavior can be traced back to variations in the microstructure and possible stress points in the fusion zone, stemming from thermal cycling and solidification [\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e]. A closer inspection of the fractured surfaces showed a clean break, with no noticeable macroscopic defects like cracks, voids, or inclusions, suggesting that the overall weld quality was quite solid.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eI utilized Scanning Electron Microscopy (SEM) to investigate the fracture mechanism thoroughly. Observing the fracture surface at a magnification of 2000\u0026times; and an accelerating voltage of 20 kV, I found evidence of mixed-mode failure, including cleavage steps, dimples, and a transition zone (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e16\u003c/span\u003e). The cleavage facets suggest that a brittle fracture has occurred due to cleavage propagation, while the dimples indicate localized plastic deformation resulting from the merging of micro-voids [\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e]. The transition zone between these two areas showcases the complex stress state and metallurgical structure of the weld metal when it faces impact loading [\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, AISI 1010 low-carbon steel was welded using the Gas Metal Arc Welding (GMAW) technique, and a comprehensive analysis of microstructural features and mechanical performance was carried out. The following conclusions can be drawn from the investigation:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eMild steel joints were successfully fabricated using the GMAW process with a single pass and no preheating. Full and defect-free penetration was achieved using ER70S-6 filler wire under controlled parameters, and the resulting bead geometry was uniform and sound.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe fusion zone (WZ) exhibited a fine-grained dendritic structure due to quenching, while the heat-affected zone (HAZ) presented varied microstructural transformations, including coarse and fine subzones. Notably, the formation of martensite in the fusion zone due to water quenching contributed to increased hardness.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eMechanical testing revealed that while the welded joints exhibited adequate tensile strength and ductility, fractures consistently occurred at the center of the weld during tensile loading, indicating that the fusion zone was the weakest region. The face bend test showed significant bending deformation; however, surface cracking and delamination were evident along the weld line. These observations suggest the presence of incomplete fusion and potential internal defects such as slag inclusions or porosity, which compromised the joint's structural integrity under bending stress. Despite these discontinuities, the Charpy impact test results demonstrated moderate energy absorption capacity, suggesting that the welded joint retains a degree of toughness, albeit with localized weaknesses.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSEM fractography revealed a combination of ductile and brittle fracture features across different test zones. Ductile dimples, intergranular tearing, and cleavage facets indicated complex failure mechanisms governed by thermal history and local microstructural variations.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eOverall, the GMAW process was found to be effective for welding AISI 1010 steel, yielding joints with balanced strength, hardness, and toughness. Future work may explore optimized welding parameters, such as arc voltage, current, and travel speed, on fusion quality and defect minimization. Additionally, employing preheating, multi-pass welding techniques, or post-weld heat treatments (PWHT) may improve weld integrity by reducing residual stresses and promoting more homogeneous microstructures. Such approaches can contribute to enhancing both the strength and toughness of welded joints in structural applications.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors declare that no external funds or research grants were received for this study. Laboratory facilities were accessed with institutional support. Scanning Electron Microscopy (SEM) analysis was conducted with the author's personal funding.\u003c/p\u003e \u003cp\u003eCompeting Interests\u003c/p\u003e \u003cp\u003eThis work was initially carried out as part of an academic course project. Additional testing was conducted independently by the author using personal resources, without any external financial support, to enhance the quality and completeness of the study. The research was undertaken solely for academic development and to gain research experience. The author declares no financial interests or personal relationships that could have influenced the research.\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e \u003cp\u003eThe author solely conceived and designed the study. Material preparation, data collection, experimental work, analysis, and interpretation were all carried out by the author. The manuscript was written and revised entirely by the author, who read and approved the final version.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe author gratefully acknowledges Professor Dr. H.M. Mamun Al Rashed and Lecturer Abrar Daiyan of the Department of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology (BUET), for their academic guidance and for facilitating access to laboratory resources throughout this investigation. Their support during the experimental phase and insightful instructions on the research methodology were invaluable. This work was conducted as part of an individual academic laboratory project without external funding; some experimental procedures were self-financed by the author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePattanayak S, Sahoo SK (2021) Gas metal arc welding based additive manufacturing\u0026mdash;a review, May 01, Elsevier Ltd. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cirpj.2021.04.010\u003c/span\u003e\u003cspan address=\"10.1016/j.cirpj.2021.04.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNarwadkar A, Bhosle S (2016) Optimization of MIG Welding Parameters to Control the Angular Distortion in Fe410WA Steel, Materials and Manufacturing Processes, vol. 31, no. 16, pp. 2158\u0026ndash;2164, Dec. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/10426914.2015.1127939\u003c/span\u003e\u003cspan address=\"10.1080/10426914.2015.1127939\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eG\u0026uuml;ral A, Bostan B, \u0026Ouml;zdemir AT (2007) Heat treatment in two phase region and its effect on microstructure and mechanical strength after welding of a low carbon steel. 28(3):897\u0026ndash;903. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.matdes.2005.10.005\u003c/span\u003e\u003cspan address=\"10.1016/j.matdes.2005.10.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. 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A comprehensive evaluation combining optical microscopy, Rockwell B hardness profiling, Optical Emission Spectroscopy (OES), tensile testing, Charpy impact testing, and Scanning Electron Microscopy (SEM) was conducted. The weld zone (WZ) exhibited dendritic solidification and recorded the highest hardness, while the heat-affected zone (HAZ) showed a significant reduction due to thermal softening and grain coarsening. Tensile testing revealed a peak strength of 461.14 MPa, with fracture localized in the WZ, indicating it as the weakest region under axial loading despite its higher hardness. Face bend testing confirmed overall ductility, although surface cracking and delamination at the weld interface indicated incomplete fusion and internal discontinuities. SEM analysis revealed mixed-mode fracture behavior, including ductile dimples, cleavage planes, and intergranular tearing. Charpy impact testing at sub-zero temperatures further confirmed reduced fracture toughness in the fusion zone. These findings underscore that while GMAW can produce structurally sound joints in AISI 1010 steel, localized heterogeneities\u0026mdash;particularly within the WZ\u0026mdash;may compromise reliability. With optimized process control and defect monitoring, GMAW remains a viable and cost-effective welding solution for low-carbon steel structural applications.\u003c/p\u003e","manuscriptTitle":"Decoding Microstructural Heterogeneity and Mechanical Anomalies in GMAW of AISI 1010 Steel through Multi-Technique Characterization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 03:17:30","doi":"10.21203/rs.3.rs-6769543/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"665a68d0-87ab-4a73-bc04-6f716e432b9b","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-19T07:47:12+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-20 03:17:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6769543","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6769543","identity":"rs-6769543","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}