The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets

The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets | 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 The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets Tian Gao, Mingmei Tang, Pengcheng Zhao, Guoshuai Yan, Lulu Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7005471/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract The corrosion resistance of laser-welded joints in ultra-pure B430LNT ferritic stainless-steel sheets stabilized with titanium and niobium was investigated in this study. The pitting resistance of the welded joints was evaluated by conducting immersion and potentiodynamic polarization tests. The intergranular corrosion resistance was assessed by chemical acid etching tests and double-loop electrochemical potentiokinetic reactivation methods. The passive films on the surfaces of welded joints were analyzed by using electrochemical impedance spectroscopy tests. The results indicate that the microstructure of welded joints are as-welded, consists of large columnar and small equiaxed grains. Pitting corrosion occurs in the heat-affected zone and fusion zone, with the majority of pits in the heat-affected zone being parallel to the fusion line. The base metal demonstrates better resistance to intergranular corrosion compared to the fusion zone, and the stability of the passive films at the base metal is greater than that of the welded joint. The Ti and Nb in welded joints do not work as effectively as they do in the base metal. The high content of chromium in the metal matrix and absorption of nitrogen from the shielding gas promote the formation of chromium carbonitrides at grain boundaries, leading to the creation of chromium-depleted zones. The formation of Cr and Ti carbonitrides near the surfaces of welded joints decreases the stability of the passive films and promotes pitting corrosion. The various factors render the welded joint area susceptible to corrosion. B430LNT ferritic stainless steel corrosion resistance laser-welded joint microstructure IGC pitting corrosion 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 1. Introduction Ferritic stainless steels (FSSs) are well known for their exceptional resistance to stress corrosion cracking, pitting, and crevice corrosion, especially in environments rich in chloride ions [ 1 – 3 ] . As a result, they are widely used in various applications such as exhaust systems, washing machines, and food processing equipment [ 4 – 6 ] . Globally, due to the increasing costs of nickel over the last few decades, there has been a noticeable trend of replacing austenitic stainless steels (ASSs) with FSSs in the chemical industry, food processing, and building decoration. This shift underscores the economic significance and growing popularity of FSSs [ 7 ] . Among the shaping technologies for FSSs, laser beam welding (LBW) is distinguished as an efficient and cost-effective method for joining sheets in industrial fabrication [ 8 ] . However, the rapid melting and solidification that occur within the joint region can adversely impact the microstructures of the fusion zone (FZ) and heat-affected zone (HAZ). These alterations could potentially compromise the corrosion resistance of both the welded joint and the adjacent base metal (BM) [ 9 ] . Several initiatives have been undertaken to understand the corrosion mechanisms inherent in FSS and to develop effective countermeasures [ 10 – 12 ] . The prevailing consensus attributes the decrease in corrosion resistance of FSS to the phenomenon of chromium depletion, which leads to intergranular corrosion (IGC) [ 13 , 14 ] . This scenario occurs when chromium-rich carbides, notably M 23 C 6 , precipitate along grain boundaries, resulting in chromium-depleted zones in neighboring grains. To improve the IGC resistance of FSS, strategies such as reducing carbon and nitrogen content, applying solid solution treatments [ 15 ] , and incorporating stabilizing elements such as titanium and niobium [ 16 , 17 ] are employed. Pertinently, Ti and Nb exhibit specific chemical affinities for carbon and nitrogen, which could potentially inhibit the formation of chromium-rich phases at grain boundaries. Reduced corrosion resistance poses a unique challenge in welded FSS joints, regardless of the welding method used [ 18 ] . When compared to arc welding, LBW presents a more complex scenario for properly understanding the corrosion resistance of these joints, especially in agent-stabilized FSS. This complexity stems from the combination of the BM itself and the distinctive features of LBW, including high energy density, minimal heat input, and rapid cooling rates. Generally, the concentrated heat input associated with LBW results in a smaller weld seam, which typically enhances corrosion resistance compared to arc welding [ 19 ] . Essentially, the chemical composition and microstructure of welded joints differ from those of the BM after welding, which have varying effects on intergranular and pitting corrosion resistance. The distribution and quantity of newly formed Cr, Ti and Nb carbides or nitrides during welding influence IGC and pitting corrosion in various ways. Stabilizing elements may accumulate at grain boundaries by interacting with carbon and nitrogen [ 20 , 21 ] , theoretically enhancing resistance to IGC, they could also potentially compromise pitting resistance. Jong Min Kim et al. [ 22 ] found that the pitting resistance and IGC of flux-cored wire welded FSS joints are improved with the increased addition of Ti and Nb, which raises the pitting potential and reduces the critical current density. Niklas Sommer et al. [ 23 ] observed the precipitation of M 23 C 6 carbide in HAZ and BM of laser-welded AISI 430Ti joints, which results in unpassivated edges of the sensitized ditches and strengthens the intergranular attack within the weld seam. Shun Tokita et al. [ 24 ] noted that Nb carbide in the as-welded joint promotes pitting corrosion by serving as both the initiation site and the core of the corrosion process. Yanze Yang et al. [ 25 ] identified Cr 2 N precipitation within the ferrite grains of the laser-welded UNS S31803 joint, which corresponds to impaired pitting corrosion resistance. Mingxu Sun et al. [ 26 ] also found significantly more chromium-rich carbide particles dispersed in the weld zone than in the BM. Moreover, the (Ti,Cr)N particles and Ti-rich inclusions formed in surface regions of welded joints promote pitting corrosion through a different mechanism. Yuyang Hou et al. [ 27 ] reported that protective passive films are susceptible to breaches or damage due to cracks that develop around particles with a different coefficient of thermal expansion compared to the steel substrate. Consequently, pits can initiate from these cracks during thermal cycling, even in the absence of a chromium-depleted zone. S. M. Gateman [ 28 ] revealed the TiN-rich inclusion on exposed steel surfaces in corrosive environments can form a galvanic couple with the matrix due to their higher corrosion potential ( E corr ). Therefore, these inclusions act as initiation sites for localized corrosion. Furthermore, the rapid phase transformation and evaporation of Ti/Nb in the weld pool during welding can significantly alter the content and distribution of Ti/Nb within the joints. This alteration may result in a corrosion resistance that differs from that of the BM [ 29 ] . The present study aims to comprehensively investigate the corrosion resistance properties of laser-welded butt joints fabricated from ultra-pure sheets of 430 FSS stabilized with Ti and Nb. The assessment of pitting resistance was carried out through immersion tests (ASTM G48-11), while susceptibility to intergranular attack was evaluated using the oxalic acid etch test and the ferric sulfate-sulfuric acid test (ASTM A763-15). To examine the electrochemical corrosion behaviors of the welded joints, we employed potentiodynamic polarization, double-loop electrochemical potentiokinetic reactivation (DL-EPR), and electrochemical impedance spectroscopy (EIS) tests. The microstructures of the joints, both before and after corrosion, were analyzed using optical microscopy and scanning electron microscopy. Additionally, energy dispersive spectroscopy (EDS) was utilized to analyze the elemental distribution after corrosion, aiding in the identification of the primary causes of corrosion. 2. Materials and methods 2.1 Materials and welding The base metal utilized in this study is B430LNT, which was derived from 022Cr17NbTi (GB/T 3280 − 2015) by adjusting the composition of specific elements. It is composed of 0.02% carbon, 0.02% nitrogen, 0.27% silicon, 0.39% manganese, 0.01% phosphorus, 0.002% sulfur, 0.11% titanium, 0.15% niobium, 17.53% chromium, 0.18% nickel, and the rest is iron. As the content of both C and N is restricted to no more than 0.02%, it is classified as a special ultrapure 430 FSS. The material used for welding is 0.7 mm thick and has undergone cold rolling and annealing. Welding was performed using a fiber laser, specifically the IPG YLS-2000-TR. This laser possesses a rated power of 2 kW and operates at a wavelength of 1070 nm. Nitrogen (99.99%) was used as the shielding gas on both sides of the weld joint, with a gas flow rate of 38 L/min on the face side and 10 L/min on the root side. The laser power and welding speed are 1.05 kW and 3.6 m/min, respectively. The beam diameter was 300 µm, and the off-focus value is 0 mm. The welding schemes are provided in Fig. 1 . The ultimate product to be welded is a cylindrical drum inside a commercial washing machine. Before welding, the B430LNT sheets underwent degreasing with acetone and rinsing with alcohol, and then drying to ensure that the base metal was free from moisture and contaminants. After punching, the two edges of the sheet were precisely aligned to create a square groove joint with a gap of less than 0.1 mm. Laser welding started from one end of the paired line and extended to the other end, creating a longitudinal weld bead. After welding, some test samples were selected from the silver-white welded drums that had no visible defects. All joint specimens were cut from the welded samples using a wire EDM machine. 2.2 Metallographic analysis After grinding with successive grades of abrasive papers up to 2000 grit and then mechanically polished to a mirror finish using 2.5 µm diamond pastes, the specimens designated for metallographic analysis were subjected to ultrasonic cleaning to remove surface impurities. Subsequently, they were immersed in a ferric chloride solution (FeCl 3 : HCl = 10 g: 100 mL) for approximately 15 seconds. Following this, each specimen was thoroughly rinsed with anhydrous ethanol and swiftly dried using a cold air stream. Finally, optical microscopy was employed to examine the physical microstructures and phases. 2.3 Immersion tests The ASTM G48-11 standard was used to test the pitting corrosion resistance of LBW joints. To minimize the influence of residual stresses induced by cutting, the edges of the specimens were ground and polished, while the face and root surfaces were retained in their original condition. The specimens were then cleaned using ultrasonic cleaning and absolute alcohol. After measuring their dimensions, the specimens were placed in a drying oven for 24 hours and weighed with a precision of 0.0001 g. Both the base metal and weld specimens were immersed in a 6% (wt.) FeCl 3 ·6H 2 O solution for 24 hours at room temperature and at 35°C, respectively. After immersion, the items were cleansed, dried, and then reweighed to determine the amount of weight lost. 2.4 IGC tests Intergranular corrosion (IGC) tests for the joints and BM were conducted in line with the ASTM A763-15 standard. The oxalic acid etch test was carried out following the procedure outlined in Practice W. The specimens, serving as the anodes, were etched at a current density of 1 A cm –2 for 90 seconds in a 10% oxalic acid solution. At the same time, a stainless steel sheet was used as the cathode. After etching, the specimen surfaces were examined for IGC using an optical microscope. The etched structures are classified as step, dual, and ditch structures. The presence of one or more grains completely surrounded by ditches indicates IGC. The ferric sulfate-sulfuric acid test was conducted in accordance with Practice X. Initially, distilled water, sulfuric acid, and ferric sulfate were carefully added into an Erlenmeyer flask. The condenser and the cooling water were then connected to the flask. The solution was boiled to fully dissolve the solid. The specimen was then immersed in the boiling solution for 24 hours. Subsequent to immersion, the samples were evaluated for microscopic examination. 2.5 Electrochemical tests The CHI660E electrochemical workstation (Shanghai Chenhua Co., Ltd) was instrumental in conducting a variety of electrochemical tests. These tests included the double loop electrochemical potentiokinetic reactivation (DL-EPR) test, potentiodynamic polarization test, and electrochemical impedance spectroscopy (EIS) test. A three-electrode cell configuration was employed, with the specimen serving as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode (SCE) as the reference electrode. To ensure the reliability of the results, each electrochemical test was conducted at least three times. The data obtained from these tests was interpreted based on equivalent electrical circuits using CS Studio 5. Prior to testing, the specimens were encapsulated in epoxy resin and connected with wires. All specimens were polished to achieve a mirror-finished surface with an exposed area of 1 cm 2 . As the HAZ was too narrow to be separated from FZ, the specimens to be tested are pure BM and welded joints which contain FZ, HAZ and BM. The solution used in DL-EPR was prepared by dissolving 0.05 mol/L H 2 SO 4 and 0.0001 mol/L KSCN in distilled water at 25°C. The specimens were first cathodically polarized at -700 mV (vs. SCE) to remove any existing surface oxides. Then, they were exposed to an open circuit potential (OCP) for a sufficient duration until the rate of potential change was less than 2 mV/h. The specimens were anodically polarized into the passive region from − 600 mV to 200 mV at a rate of 3 mV/s, showing an activation current ( I a ). The scan direction was then reversed to the initial potential at a rate of 1.67 mV/s, displaying a reactivation current ( I r ). The susceptibility to IGC can be quantified by the R a value, calculated as R a = I r / I a ×100%. A higher R a value indicates a higher susceptibility to IGC. In the potentiodynamic polarization tests, the exposed area of the specimens was limited to 1 cm 2 . First, a 180-minute open circuit potential test was conducted to ensure the stability of the system. The tests were performed in a 3.5% NaCl solution, starting from-1.2V SCE to 0.5 V SCE at a scanning rate of 0.167 mV/s. Following a stabilization period at open circuit potential until the dummy cell potential is 0 V versus the open circuit potential, EIS tests were carried out using 5 mV AC signals across a frequency range of 100 kHz to 0.01 Hz. Similar to the potentiodynamic tests, the EIS tests were also conducted in a 3.5% NaCl solution. 3. Results 3.1 Microstructure The cross-sectional profile and microstructural characteristics of the welded joint are depicted in Fig. 2 . The weld exhibits full penetration, resulting in the formation of an FZ that resembles a distorted cup. Within the FZ, coarse columnar grains grow from the fusion boundaries on both sides and converge toward the center of the weld pool, ultimately meeting at the centerline of the weld bead. The high travel speed and intense heat input during the welding process lead to a considerable reduction in the size of the HAZ, which makes it challenging to distinguish the boundaries between the HAZ and the FZ. Furthermore, the boundaries between the HAZ and the BM are indistinct due to the similar grain sizes in both areas. The rapid cooling rate experienced on both the face and root sides of the weld facilitates the formation of fine equiaxed grains at the centerlines of these surfaces, primarily through heterogeneous nucleation. Nucleation substrates for the formation of new grains within the weld pool are phases of chemical compounds containing titanium and Nb, which have high melting points. The grains in the HAZ and BM exhibit identical shapes and sizes, indicating that the laser power had no significant impact on them. 3.2 Pitting corrosion 3.2.1 Solution immersion After a 24-hours of immersion in a ferritic chloride solution at 35°C, the morphology on both the face and root sides of a specimen is depicted in Fig. 3 . A notable disparity in the number, size, and distribution of pits between the two sides has been observed. It is clear that more pits are formed on the face side than on the root side. On the face side, there is a higher incidence of pits, with larger corrosion pits predominantly forming in the BM rather than in the FZ. These pits are characteristically aligned parallel to the fusion boundary. On the root side, the FZ exhibits a greater density of pits compared to the BM. Moreover, the pits on the root side are of a smaller size. The regular distribution of pits in the BM, as depicted in Fig. 3 (a), can be attributed to microstructural alterations caused by the concentrated heat input during welding. The preferential corrosion near the fusion boundary indicates that the integrity of the passive film has been compromised, suggesting the emergence of a chromium-depleted zone in this area. The face side of the weld demonstrates a more pronounced susceptibility to pitting attack compared to the root side. This observation suggests that the laser heating process affects the structures of both the welded joint and the adjacent BM, impeding the ability of the passive film to resist pitting corrosion. Furthermore, because the root side demonstrates greater resistance to pitting corrosion, it is less impacted by the heat generated from the laser compared to the face side. From this point, the HAZ in a laser-welded FSS joint is not as narrow as depicted in Fig. 2 . In fact, it extends beyond the region where pits appear parallel to the fusion boundaries. Figure 4 presents the mass loss rates of both the BM and the welded joint following the immersion test. At room temperature, the BM displays a mass loss rate of 58 mg m -2 h -1 , indicative of its superior resistance to pitting corrosion compared to the welded joint. The pattern is consistently replicated at 35°C. Conversely, the welded joint exhibits a worse performance in pitting corrosion, with a mass loss rate of 162 mg m -2 h -1 . Across all temperature, the mass loss rate of the BM is consistently lower than that of the welded joint, suggesting a reduction in the pitting corrosion resistance after welding. Most notably, since the mass loss rate of the specimen at room temperature is significantly lower than that at 35°C, the pitting resistance of the specimen diminishes as the temperature increases. This effect is more pronounced in the welded joint, where the rate of mass loss escalates more rapidly than in the BM with rising temperature. Therefore, it can be concluded that the pitting resistance of laser-welded B430LNT FSS joints is compromised after welding, and the corrosion rate escalates with an increase in temperature. 3.2.2 Potentiodynamic polarization curves Figure 5 (a) shows the OCP ( E op ) results of BM and welded joint. The essentially constant OCPs over 180 minutes, during which the value of the BM exceeds that of the welded joint, indicate that the system is thermodynamically stable. Figure 5 (b) illustrates the potentiodynamic polarization curves of the welded joint and BM in a 3.5% NaCl solution, while Fig. 5 (c) shows the corrosion potentials ( E corr ) and corrosion currents ( I corr ) of BM and welded joint. Table 1 enumerates the specific electrochemical polarization parameters that were fitted by the extrapolation of the Tafel lines. Table 1 Electrochemical polarization parameters Specimens E corr (V) I corr (µA/cm 2 ) E pit (V) C R (mm/a) R p (kΩ•cm 2 ) BM -0.229 ± 0.004 0.98 ± 0.14 0.044 ± 0.001 0.004 ± 0.002 18.86 ± 0.5 Welded joint -0.327 ± 0.015 1.95 ± 0.21 -0.057 ± 0.003 0.063 ± 0.001 16.45 ± 0.2 Pitting corrosion of ferritic stainless steel can be characterized by three distinct stages: initiation, metastable propagation, and stable propagation. Pitting corrosion typically initiates in non-homogeneous areas, where the local breakdown passive films occur. The abrupt failure of the protective film allows the exchange of electrolytes with acidic electrolytes within the pits. This exchange restores the pH to its original level, thereby facilitating the spontaneous repassivation of the steel. This process is commonly known as metastable pitting growth. Figure 5 indicates that the polarization curve of the BM exhibits a more pronounced metastable pitting potential range compared to that of the welded joint. The critical pitting potential ( E pit ) is identified by an inflection point on the polarization curve. It is represented the lowest positive potential at which pits do not form, and the potential above which stable pits nucleate and grow. The E pit values for the BM and welded joint are 0.044 V and − 0.057 V, respectively, indicating that BM possesses greater resistance to pitting. The E corr reflects the thermodynamic corrosion tendency of materials [ 30 ] . As indicated in Fig. 5 (b) and (c), the E corr of the BM at -0.229 V is higher than that of the welded joint at -0.327 V. The welded joint exhibited higher current densities in the potential range associated with passivity, indicating inferior corrosion resistance compared to the base metal. As indicated in Table 1 , both the polarization resistance ( R p ) and the annual corrosion rate ( C R ) of BM are greater than those of the welded joint, suggesting a decrease in pitting corrosion resistance following the welding process. 3.3 Intergranular corrosion 3.3.1 Oxalic acid etch test Figure 6 displays the surface morphology of the welded joint after etching with oxalic acid. The microstructure has revealed the formation of oriented columnar grains in the FZ, while the BM retains its equiaxed grain structure. Both columnar and equiaxed grains exhibit signs of IGC along grain boundaries during the etching process. A higher density of ditches is observed in certain grain boundaries within the FZ compared to the BM. Some fine equiaxed grains at the center of the FZ are completely encircled by ditches, as shown in Fig. 6 (a). Within the indistinct HAZ, where grain sizes are similar to those in BM, the occurrence of IGC is minimal, as depicted in Fig. 6 (b). Notably, no IGC is observed in the BM and HAZ. In summary, the FZ exhibits a greater susceptibility to sensitization compared to the HAZ in the laser-welded joints of B430LNT FSS sheets. 3.3.2 Ferric sulfate-sulfuric acid test Following the ferric sulfate-sulfuric acid test, the surface morphology of a joint specimen is illustrated in Fig. 7 . The complete morphology of HAZ has been revealed. In a broad sense, the HAZ extends to areas where IGC does not occur. The FZ has an average width of approximately 300 µm, while the HAZ spans an average width of about 100 µm. IGC is observed across the FZ and HAZ, but it predominantly affects the FZ, with minimal grain boundary corrosion noted in the HAZ. In contrast, the BM exhibits the highest level of resistance to IGC within the joint structure. Figure 8 (a) reveals the grain boundaries in the FZ, particularly along the centerline of the weld, as highlighted by the chemical immersion process. Significant undissolved precipitates are exposed along these grain boundaries, as shown in Fig. 8 (b). The body-centered cubic (bcc) lattice of FSS has a lower solid solubility of interstitial atoms, such as C and N, compared to the face-centered cubic (fcc) lattice. Therefore, the diffusion of these elements within the grains is accelerated under the thermal cycling conditions caused by LBW. This acceleration contributes to the formation of precipitates, resulting in pronounced IGC in the FZ. Due to the concentrated heat input of the laser and the rapid cooling of the sheet joints, grain coarsening in the HAZ is suppressed, resulting in a smaller grain size compared to the FZ. Moreover, fewer particles precipitate along the grain boundaries in the HAZ, leading to only a mild degree of IGC in this area of the laser-welded joint. Therefore, it is deduced that the FZ shows the highest susceptibility to IGC within the joint. Figure 9 presents the results of the EDS analysis conducted on the surface of a joint specimen after corrosion, with a focus on the distribution of key elements across the grain structure. Despite the corrosion, fine precipitates are still visible along the grain boundaries. Notably, C and N atoms are found to aggregate along these boundaries, while Cr atoms are noticeably absent in the areas of corrosion pits. This observation suggests that particles enriched with carbon and nitrogen segregate along the grain boundaries after the welding process. It is possible that some of the N content could have come from the shielding gas used during welding. The reduced concentration of Cr atoms at the grain boundaries weakens the ability to maintain the formation of passive films, thus promoting the occurrence of IGC in these regions. Meanwhile, Ti, Nb, and Si exhibit a uniform distribution across the examined area, indicating that their distribution remains unaffected by the thermal cycling experienced during welding. The separated Nb on the steel surface can stabilize the passive film of the stainless steel and increase the thickness of the passive film of the steels [ 31 , 32 ] . This film can hinder the breakdown of the matrix in hydrochloric and sulfuric acid solutions. In a sulfuric acid environment, Nb can assist in the formation of an iron oxide film, thereby increasing the thickness and density of the protective layer. However, Nb exhibits a stronger affinity for C and N compared to Cr. During the welding process, Nb atoms tend to bond with C and N, leading to their precipitation at grain boundaries. The formation of Nb(C, N) precipitates creates a potential difference between these particles and the substrate, which can lead to preferential corrosion in areas with concentrated precipitates, ultimately resulting in the formation of pits. Consequently, Ti and Nb are less effective in enhancing the corrosion resistance of laser-welded joints in FSS compared to their impact in BM. Figure 10 displays the results of the SEM and EDS analyses conducted on the precipitates found at the grain boundaries in the FZ of B430LNT FSS after laser welding. The analysis revealed the presence of chromium and titanium carbonitrides at these grain boundaries, while niobium precipitates were notably absent. The absence of niobium precipitates could be attributed to their dissolution at the elevated temperatures experienced during welding. In comparison to the Nb content, the Cr content in B430LNT FSS is much higher, resulting in the preferential precipitation of chromium carbonitrides at the grain boundaries. This phenomenon results in the formation of chromium-depleted zones, which subsequently promote IGC. Furthermore, the presence of titanium precipitates at the grain boundaries can negatively impact the stability of the adjacent passivation film. These precipitates can generate a potential difference between the grain boundary and the substrate, resulting in preferential dissolution. This process further exacerbates the occurrence of IGC, making the welded joints more susceptible to this type of corrosion. 3.4 DL-EPR Figure 11 illustrates the results of the DL-EPR experiments, focusing on the reactivation current density ( I r ) to the activation current density ( I a ) of the specimens. Generally, the ratio ( R a ) of I r to I a indicates the degree of sensitization in a specimen. As depicted in Fig. 11 (a), there is no significant increase in the I r value for the welded joint. Since it is difficult to separate an entire welded joint from its BM due to the indistinct boundaries between the BM and HAZ, the welded joint sample unavoidably contains a portion of the BM, influencing the experimental results. As shown in Fig. 11 (b), the calculated R a values of the BM and welded joint are 0.47% and 1.13%, respectively. These findings suggest that the welded joint shows some level of sensitization after laser welding. It is important to note, however, that the R a value can be directly influenced by various factors, such as the experimental temperature and the concentration of the solution used [ 33 ] . Given these influencing factors, making direct comparisons between the R a values of the BM and the laser-welded joints may not provide completely accurate insights into their relative sensitization levels. Figure 12 (a) shows the microstructure of the BM after the DL-EPR test. This microstructure is characterized by a dense arrangement of small equiaxed grains, typically formed during the annealing process. Notably, there is an absence of significant IGC at the grain boundaries, indicating the inherent corrosion resistance of the BM. In contrast, Fig. 12 (b) depicts the microstructure of the FZ. This area is distinguished by the presence of coarse grains, which are a direct result of the welding process. These grains are scattered across the visual field and are accompanied by severe IGC at their boundaries. The observed IGC within the FZ highlights its increased susceptibility to corrosion compared to the BM. The results collectively suggest that the laser welding process disrupts the effectiveness of the stabilizing agents added to the steel. Consequently, the corrosion resistance of the welded joints shows a marked deterioration. The decline in corrosion performance is primarily attributed to the variations in the microstructure induced by the welding process. 3.5 EIS tests EIS was employed to further examine the effect of laser welding on the passive film of FSS. Figure 13 presents the Nyquist and Bode plots for both the BM and the welded joint at 25°C in a 3.5 wt% NaCl solution. In the Nyquist plots, two incomplete capacitive semicircles are evident, as illustrated in Fig. 13 (a). The polarization resistance can be indirectly inferred from the diameter of the semicircle [ 34 , 35 ] . The diameter of the semicircle arc is correlated with the corrosion resistance of the passive film [ 36 ] . It is evident from Fig. 13 (a) that the semi-arc diameter of the welded joint is smaller than that of the BM, indicating a lower polarization resistance and reduced corrosion resistance. The Bode plots illustrate the impedance modulus value and phase angle at various frequencies. In the low-frequency range, the logarithmic value of |Z| for BM is higher, indicating greater polarization resistance [ 37 – 39 ] . The impedance model at low frequencies aligns with the capacitive arc radius law in the Nyquist plots. Additionally, in the low-frequency domain, the phase angle values of the BM exceed those of the welded joint. It is well established that the welded joint with a lower impedance value and a more positive phase angle exhibits poorer corrosion resistance compared to the BM. An equivalent circuit model was utilized to represent the electrochemical system and to fit the impedance data obtained from the EIS measurements, as is depicted in Fig. 13 (a). In this model, R e reprents the electrolyte resistance, R f represents the passive film resistance, and R ct represents the charge transfer resistance. In addition, Q f represents the capacitance of the passive film, while Q dl represents the capacitance of the double layer. Table 2 provides the detailed circuit parameter values acquired after fitting the experimental EIS data with the equivalent circuit model R e ( Q f ( R f ( Q dl R ct ))), and the chi-squared errors (χ 2 ) in Table 2 validate the equivalent circuit model for the passive film system. Due to the non-homogeneity of the FSS surface, the capacitance measured for the passivated film is likely to deviate from the ideal capacitance. Therefore, the constant phase element Q is used to replace the capacitor C during fitting. The impedance of Q is represented in the following form: Where Q is the constant phase element of the electrode, j is the imaginary unit, ω represents the angular frequency, and n is the constant phase index [40] . Typically, n has a value between 0 and 1. If n is close to 1, Q represents the ideal capacitance. The total impedance Z (ω) can be evaluated using the following relation. As shown in Table 2 , the welded joint exhibits relatively low R f and R ct values, indicating that laser welding may compromise the corrosion resistance. In contrast, the higher R f and R ct values for the BM suggest limited migration of electrons and/or ions across the passive film and interface, which implies better corrosion resistance for the BM [ 41 , 42 ] . The parameters n f and n dl represent the dispersion coefficients of Q f and Q dl , respectively. Since n dl deviates significantly from 1 compared to n f , the double-layer capacitance is not ideal. Additionally, the Q f and Q dl values for the BM are greater than those for the welded joint. Table 2 also indicates that the electrolyte resistance ( R e ) of the welded joint slightly decreases compared to that of the BM. These findings suggest that the protective performance of the passivation film in the welded joint is inferior to that in the BM. Table 2 Equivalent circuit parameters for the EIS of the BM and Welded joint Specimens R e (Ω.cm 2 ) R f (Ω∙cm 2 ) Q f (×10 − 5 .cm − 2 ) n f R ct (Ω∙cm 2 ) Q dl (×10 − 5 F.cm − 2 .) n dl χ 2 (×10 − 3 ) BM 12.42 ± 0.16 7.14 ± 0.1 4.84 ± 0.16 0.91 ± 0.01 3.19 ± 0.16 1.63 ± 0.26 0.50 ± 0.01 2.86 ± 0.4 Welded joint 10.13 ± 0.26 3.42 ± 0.09 5.67 ± 0.18 0.90 ± 0.03 1.80 ± 0.02 3.02 ± 0.11 0.55 ± 0.01 2.42 ± 0.3 4. Discussion Based on the characterization of microstructure, electrochemical testing, corrosion morphology, and elemental scanning analysis, Fig. 14 schematically illustrates the changes in element distribution and the formation of precipitates during the laser welding process, as well as the corresponding decrease in corrosion resistance of the joint. In this figure, hexagonal symbols represent the grains in the matrix, while geometric shapes in various colors denote different elements and their compounds. In particular, the variation in colors along the grain boundaries indicates the integrity of the passivation film. After annealing, the initial distribution of elements and compounds in BM grains is illustrated in Fig. 14 (a). Both niobium and titanium carbonitrides are formed and evenly distributed throughout the grains and their boundaries. The absence of these carbonitrides on the surfaces of the BM correlates with a reduced risk of pitting corrosion [ 43 ] . The welding process induces significant changes in the microstructure. During the melting stage, specific compounds in the welding zone decompose at elevated temperatures. Nitrogen from the shielding gas permeates the weld pool both physically and chemically. The high temperature generated by the laser beam creates conditions that favor the formation of carbonitrides within the weld pool [ 23 , 44 ] . Meanwhile, certain metallic and nonmetallic elements evaporate due to the high temperature. All elements, with the exception of certain carbonitrides, dissolve in the liquid metal [ 45 , 46 ] . During the cooling stage, Ti(C,N) and Nb(C,N) particles with high melting points are formed in the weld pool owing to their strong affinity for C and N. These solid particles act as substrates for crystal nuclei and promote heterogeneous nucleation. Subsequently, numerous equiaxed grains develop at the center of the FZ. The relatively small average grain size facilitates the diffusion of Cr, Ti, and Nb to the grain boundaries. Additionally, the solid solubility of interstitial elements such as C and N in the bcc lattice of FSS decreases after solidification. This reduction in solubility increases the diffusion of solute atoms [ 47 ] . Although the rapid cooling rate may impede the precipitation of secondary phases, which is beneficial for improving corrosion resistance [ 8 ] , metallic carbonitrides do precipitate along these grain boundaries, as shown in Fig. 10. These phenomena account for the primary distribution of carbonitrides at the centers and edges of the grains. The intentional incorporation of Ti and Nb does increase their competitive binding to N and C in comparison to Cr. However, chromium carbonitrides continue to form at the grain boundaries in LBW due to the high chromium content, elevated welding temperatures, and nitrogen absorption. Figure 14 (c) shows that chromium-depleted zones develop as a result of the precipitation of chromium carbonitrides after welding, even in the presence of Ti and Nb [16, 48]. Consequently, laser-welded FSS joints are more susceptible to IGC. Furthermore, chromium-deficient regions and carbonitrides at the grain boundaries hinder the continuous formation of a passive film in the welded joints. The presence of titanium carbonitrides can create an electric potential difference with the matrix, leading to instability and a lack of integrity in the passive film, as illustrated in Fig. 14 (d). Therefore, IGC and pitting corrosion occur at the grain boundaries, as depicted in Fig. 6 . 5. Conclusion In this study, the effects of laser welding on the pitting and intergranular corrosion resistance of thin plates of ferritic stainless steel with stabilized elements niobium and titanium were investigated. An in-depth analysis led to the following conclusions. (1) Pitting is likely to occur on the face side of laser-welded FSS joints, specifically in HAZ that runs parallel to the fusion line and along the centerline of FZ. The pitting corrosion is primarily due to the concentrated heat input, which leads to the formation of chromium-depleted zone in the HAZ, thereby compromising the ability of surface layers to sustain a protective passive film. Since the root side exhibits greater resistance to pitting corrosion, it is less impacted by the laser heat. (2) The weight loss measurements and the potentiodynamic polarization curves show that the pitting resistance of laser-welded B430LNT FSS joints is compromised. The corrosion rate of welded joints increases with an increase in temperature. The decrease of both E pit and E corr in welded joints implies a reduction in pitting resistance after welding. (3) Results from the oxalic acid etch test, the ferric sulfate-sulfuric acid test, and DL-EPR curves reveal that the welded joint is more prone to IGC, in contrast to the BM. IGC takes place predominately at grain boundaries in FZ, and secondarily at grain boundaries in HAZ. Precipitates formed along the grain boundaries during the LBW contribute to the IGC in weld joints. (4) Despite the addition of Ti and Nb, Cr (C, N) still precipitates at grain boundaries in welded joints. The Cr-rich compounds may result from the high Cr content in the metal matrix and nitrogen absorption, which leads to chromium-depleted zones in neighboring grains. The precipitation of carbonitride at the grain boundary creates an electrochemical potential difference, resulting in electrochemical corrosion. Declarations Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This project is financially supported by the China-Ukraine Government Science and Technology Exchange Project (2022–2023) under name of Pengcheng Zhao. Authors Contributions Tian Gao conducted the experiments and drafted the manuscript. Mingmei Tang collected and analyzed the corrosion data. Pengcheng Zhao was responsible for the methodology and investigation. Guoshuai Yan performed the metallurgical analysis. Lulu Wang contributed to the editing of the manuscript. Acknowledgments This work was supported by China-Ukraine Government Science and Technology Exchange Projects (2022–2023) under the name of Pengcheng Zhao. The authors would like to thank Mr. Hongtai Liu and Yazhou Xu for their assistance in the laser welding experiments. One of our authors, Tian Gao, would appreciate Mr. Zhenhui Zhao for his advice in preparing the equipment. Data Availability Statement The data are available from the corresponding author on reasonable request. References Zheng C, Ke J-H, Maloy SA, Kaoumi D. Correlation of in-situ transmission electron microscopy and microchemistry analysis of radiation-induced precipitation and segregation in ion irradiated advanced ferritic/martensitic steels. Scripta Materialia 2019;162:460-464. https://doi.org/10.1016/j.scriptamat.2018.12.018. Wang T, Zhang HY, Liang W. Hydrogen embrittlement fracture mechanism of 430 ferritic stainless steel: The significant role of carbides and dislocations. Materials Science and Engineering: A 2022;829:142043. https://doi.org/10.1016/j.msea.2021.142043. Kim JK, Lee JS, Kim KY. 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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-7005471","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":483335199,"identity":"18ef21e0-255a-419d-9118-35ca7ebb7816","order_by":0,"name":"Tian Gao","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tian","middleName":"","lastName":"Gao","suffix":""},{"id":483335200,"identity":"b95ffb7e-b4a6-4f47-9976-533010af8bc9","order_by":1,"name":"Mingmei Tang","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Mingmei","middleName":"","lastName":"Tang","suffix":""},{"id":483335201,"identity":"6eb71b25-1681-4c3b-bb24-c7c4027480fc","order_by":2,"name":"Pengcheng Zhao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYHACNiC2QWITqSUNiJlJ03KYBC3m7MefPfhRcV52w/nzBxg+lB1m4J/dgF+LZU9CumHPmdvGG24kMzDOOHeYQeLOAfxaDG4wHJPgbbuduOEGMwMzb9thBgOJBEJaGNsk/7adS9xw/jAD81/itDCzSfO2HUjccCCZgZmRGC2WPWls0jJnko1n3kg2ONhzLp1H4gYBLaAQk3xTYSfbd/7gwwc/yqzl+GcQchiUZmwAEgeAmAe/enQto2AUjIJRMAqwAgBb70PEzO0eHgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-0123-6272","institution":"Qingdao University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Pengcheng","middleName":"","lastName":"Zhao","suffix":""},{"id":483335202,"identity":"d372e956-36c7-4da6-ae2f-8c0e872c6231","order_by":3,"name":"Guoshuai Yan","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Guoshuai","middleName":"","lastName":"Yan","suffix":""},{"id":483335203,"identity":"61a26e95-fd50-4ecf-a7cc-a9f569067327","order_by":4,"name":"Lulu Wang","email":"","orcid":"","institution":"Qingdao University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Lulu","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-06-30 02:22:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7005471/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7005471/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86656251,"identity":"892125de-d632-4636-a9e2-8d9429e53371","added_by":"auto","created_at":"2025-07-14 10:17:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":512425,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of LBW. (a) welding schematic, (b) butt joint and sliced specimen.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/65bd24ee5f523332667fc2b5.png"},{"id":86662245,"identity":"5e64faf5-8fa0-4756-8dcb-5db5fcb76466","added_by":"auto","created_at":"2025-07-14 10:41:54","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1579610,"visible":true,"origin":"","legend":"\u003cp\u003eJoint profile and its microstructures. (a) enlarged left side, (b) cross-section profile, and (c) enlarged right side.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/e4e6a5c4924277358191cb67.png"},{"id":86656257,"identity":"b1d43ec0-3435-4a1e-a8a6-6b0ce55e8548","added_by":"auto","created_at":"2025-07-14 10:17:54","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1092525,"visible":true,"origin":"","legend":"\u003cp\u003ePitting attacks in a weld after ferritic chloride pitting corrosion. (a) face side and (b) root side.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/c2b7742285d2e8eb60d7b7ef.png"},{"id":86662247,"identity":"d7a73d42-67fd-4625-9316-99765cbe4cf4","added_by":"auto","created_at":"2025-07-14 10:41:54","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1714509,"visible":true,"origin":"","legend":"\u003cp\u003eMass loss rate of BM and weld joint in immersion test.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/f6c85b4a75a7784e266cbe60.png"},{"id":86663389,"identity":"5795a3c1-80a0-4ca9-b832-a6fbed32f4c3","added_by":"auto","created_at":"2025-07-14 10:49:54","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":140365,"visible":true,"origin":"","legend":"\u003cp\u003ePotentiodynamic polarization curves of the BM and welded joint. (a) OCP tests, (b) Potentiodynamic polarization curves, and (c) the means and standard deviations of \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/9ea35ce3680b1363bb563a84.png"},{"id":86658476,"identity":"9cc1d95f-ed3e-44e7-bc79-1ac220b51528","added_by":"auto","created_at":"2025-07-14 10:25:54","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1136941,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology of joints after 10% oxalic acid etching. (a) equiaxial grains, (b) columnar grains.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/b38b5d88cd3c947698319833.png"},{"id":86656261,"identity":"0d4fc34b-4b34-4419-a718-2221cf42fbe4","added_by":"auto","created_at":"2025-07-14 10:17:54","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":3140265,"visible":true,"origin":"","legend":"\u003cp\u003eSurface morphology of a specimen after the ferric sulfate-sulfuric acid test.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/d0b00ca0128545f4024cc5e6.png"},{"id":86656260,"identity":"83950406-23d9-4020-8503-c08bc7f0d99c","added_by":"auto","created_at":"2025-07-14 10:17:54","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":321417,"visible":true,"origin":"","legend":"\u003cp\u003eThe microstructure of the FZ and HAZ after the ferric sulfate-sulfuric acid test. (a) FZ, (b) enlarged FZ grains and their boundaries, and (c) HAZ.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/815ec31aa38219fb7dc1650c.png"},{"id":86658475,"identity":"b896aa72-2cb1-45a1-afd8-6daada93beea","added_by":"auto","created_at":"2025-07-14 10:25:54","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":581096,"visible":true,"origin":"","legend":"\u003cp\u003eResults of SEM and EDS. (a)Surface morphology of welded joints after oxalic acid etching, (b) EDS mapping profiles of grains with boundary grooves in the FZ.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/04ca081c6f278523f9e9f470.png"},{"id":86660126,"identity":"70ec03b1-8785-4d05-b6f3-e7e471efa4b7","added_by":"auto","created_at":"2025-07-14 10:33:54","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":359208,"visible":true,"origin":"","legend":"\u003cp\u003eThe precipitates characterized by SEM and EDS:(a) Cr(C,N) at the grain boundaries, (b) EDS analysis of Cr (C,N), (c) Ti(C,N) at the grain boundaries, and (d) EDS analysis of Ti(C,N).\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/423f27081896e5c6e88d662d.png"},{"id":86656275,"identity":"879d6f07-d87a-426e-bdae-b3339a10e0fa","added_by":"auto","created_at":"2025-07-14 10:17:55","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":182547,"visible":true,"origin":"","legend":"\u003cp\u003eResults of the DL-EPR. (a) DL-EPR curves and (b) \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e values.\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/7b1794f79bb8e22da0017153.png"},{"id":86658481,"identity":"08f98ae8-e9c1-4824-be33-daa7e0266685","added_by":"auto","created_at":"2025-07-14 10:25:55","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":517179,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of (a) BM and (b) FZ after DL-EPR.\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/97b0d4f7f95991c5671ceefb.png"},{"id":86656270,"identity":"80d528eb-39fd-4133-805f-090048ab9b7a","added_by":"auto","created_at":"2025-07-14 10:17:54","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":113161,"visible":true,"origin":"","legend":"\u003cp\u003eEIS results of BM and welded joint in 3.5% NaCl solution. (a) Nyquist plot, (b) Bode plot.\u003c/p\u003e","description":"","filename":"floatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/698fde355af5ea461e136724.png"},{"id":86656271,"identity":"cbdd4382-1c7d-4d0f-ad04-488e224dffc0","added_by":"auto","created_at":"2025-07-14 10:17:55","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":397826,"visible":true,"origin":"","legend":"\u003cp\u003eMechanism of the laser welding effect on the microstructure and precipitates in the FZ. (a) initial element distribution within the grains, (b) laser welding process, (c) cooling processes, and (d) final element distribution status.\u003c/p\u003e","description":"","filename":"floatimage14.png","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/cad767c851e3df3aa9d692cb.png"},{"id":87467004,"identity":"f8fbc1fa-7a24-46a0-b4bf-b26180321be9","added_by":"auto","created_at":"2025-07-24 07:39:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":12598047,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7005471/v1/f731a8b9-fb22-4141-a784-42979e75d6a5.pdf"}],"financialInterests":"","formattedTitle":"The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFerritic stainless steels (FSSs) are well known for their exceptional resistance to stress corrosion cracking, pitting, and crevice corrosion, especially in environments rich in chloride ions \u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. As a result, they are widely used in various applications such as exhaust systems, washing machines, and food processing equipment \u003csup\u003e[\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Globally, due to the increasing costs of nickel over the last few decades, there has been a noticeable trend of replacing austenitic stainless steels (ASSs) with FSSs in the chemical industry, food processing, and building decoration. This shift underscores the economic significance and growing popularity of FSSs \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. Among the shaping technologies for FSSs, laser beam welding (LBW) is distinguished as an efficient and cost-effective method for joining sheets in industrial fabrication \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. However, the rapid melting and solidification that occur within the joint region can adversely impact the microstructures of the fusion zone (FZ) and heat-affected zone (HAZ). These alterations could potentially compromise the corrosion resistance of both the welded joint and the adjacent base metal (BM) \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eSeveral initiatives have been undertaken to understand the corrosion mechanisms inherent in FSS and to develop effective countermeasures \u003csup\u003e[\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. The prevailing consensus attributes the decrease in corrosion resistance of FSS to the phenomenon of chromium depletion, which leads to intergranular corrosion (IGC) \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. This scenario occurs when chromium-rich carbides, notably M\u003csub\u003e23\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e, precipitate along grain boundaries, resulting in chromium-depleted zones in neighboring grains. To improve the IGC resistance of FSS, strategies such as reducing carbon and nitrogen content, applying solid solution treatments \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e, and incorporating stabilizing elements such as titanium and niobium \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e are employed. Pertinently, Ti and Nb exhibit specific chemical affinities for carbon and nitrogen, which could potentially inhibit the formation of chromium-rich phases at grain boundaries.\u003c/p\u003e\u003cp\u003eReduced corrosion resistance poses a unique challenge in welded FSS joints, regardless of the welding method used \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e. When compared to arc welding, LBW presents a more complex scenario for properly understanding the corrosion resistance of these joints, especially in agent-stabilized FSS. This complexity stems from the combination of the BM itself and the distinctive features of LBW, including high energy density, minimal heat input, and rapid cooling rates. Generally, the concentrated heat input associated with LBW results in a smaller weld seam, which typically enhances corrosion resistance compared to arc welding \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eEssentially, the chemical composition and microstructure of welded joints differ from those of the BM after welding, which have varying effects on intergranular and pitting corrosion resistance. The distribution and quantity of newly formed Cr, Ti and Nb carbides or nitrides during welding influence IGC and pitting corrosion in various ways. Stabilizing elements may accumulate at grain boundaries by interacting with carbon and nitrogen \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e, theoretically enhancing resistance to IGC, they could also potentially compromise pitting resistance. Jong Min Kim et al. \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e found that the pitting resistance and IGC of flux-cored wire welded FSS joints are improved with the increased addition of Ti and Nb, which raises the pitting potential and reduces the critical current density. Niklas Sommer et al. \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e observed the precipitation of M\u003csub\u003e23\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e carbide in HAZ and BM of laser-welded AISI 430Ti joints, which results in unpassivated edges of the sensitized ditches and strengthens the intergranular attack within the weld seam. Shun Tokita et al. \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e noted that Nb carbide in the as-welded joint promotes pitting corrosion by serving as both the initiation site and the core of the corrosion process. Yanze Yang et al. \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e identified Cr\u003csub\u003e2\u003c/sub\u003eN precipitation within the ferrite grains of the laser-welded UNS S31803 joint, which corresponds to impaired pitting corrosion resistance. Mingxu Sun et al. \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e also found significantly more chromium-rich carbide particles dispersed in the weld zone than in the BM. Moreover, the (Ti,Cr)N particles and Ti-rich inclusions formed in surface regions of welded joints promote pitting corrosion through a different mechanism. Yuyang Hou et al. \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e reported that protective passive films are susceptible to breaches or damage due to cracks that develop around particles with a different coefficient of thermal expansion compared to the steel substrate. Consequently, pits can initiate from these cracks during thermal cycling, even in the absence of a chromium-depleted zone. S. M. Gateman \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e revealed the TiN-rich inclusion on exposed steel surfaces in corrosive environments can form a galvanic couple with the matrix due to their higher corrosion potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e). Therefore, these inclusions act as initiation sites for localized corrosion. Furthermore, the rapid phase transformation and evaporation of Ti/Nb in the weld pool during welding can significantly alter the content and distribution of Ti/Nb within the joints. This alteration may result in a corrosion resistance that differs from that of the BM \u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe present study aims to comprehensively investigate the corrosion resistance properties of laser-welded butt joints fabricated from ultra-pure sheets of 430 FSS stabilized with Ti and Nb. The assessment of pitting resistance was carried out through immersion tests (ASTM G48-11), while susceptibility to intergranular attack was evaluated using the oxalic acid etch test and the ferric sulfate-sulfuric acid test (ASTM A763-15). To examine the electrochemical corrosion behaviors of the welded joints, we employed potentiodynamic polarization, double-loop electrochemical potentiokinetic reactivation (DL-EPR), and electrochemical impedance spectroscopy (EIS) tests. The microstructures of the joints, both before and after corrosion, were analyzed using optical microscopy and scanning electron microscopy. Additionally, energy dispersive spectroscopy (EDS) was utilized to analyze the elemental distribution after corrosion, aiding in the identification of the primary causes of corrosion.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and welding\u003c/h2\u003e\u003cp\u003eThe base metal utilized in this study is B430LNT, which was derived from 022Cr17NbTi (GB/T 3280\u0026thinsp;\u0026minus;\u0026thinsp;2015) by adjusting the composition of specific elements. It is composed of 0.02% carbon, 0.02% nitrogen, 0.27% silicon, 0.39% manganese, 0.01% phosphorus, 0.002% sulfur, 0.11% titanium, 0.15% niobium, 17.53% chromium, 0.18% nickel, and the rest is iron. As the content of both C and N is restricted to no more than 0.02%, it is classified as a special ultrapure 430 FSS. The material used for welding is 0.7 mm thick and has undergone cold rolling and annealing.\u003c/p\u003e\u003cp\u003eWelding was performed using a fiber laser, specifically the IPG YLS-2000-TR. This laser possesses a rated power of 2 kW and operates at a wavelength of 1070 nm. Nitrogen (99.99%) was used as the shielding gas on both sides of the weld joint, with a gas flow rate of 38 L/min on the face side and 10 L/min on the root side. The laser power and welding speed are 1.05 kW and 3.6 m/min, respectively. The beam diameter was 300 \u0026micro;m, and the off-focus value is 0 mm. The welding schemes are provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eThe ultimate product to be welded is a cylindrical drum inside a commercial washing machine. Before welding, the B430LNT sheets underwent degreasing with acetone and rinsing with alcohol, and then drying to ensure that the base metal was free from moisture and contaminants. After punching, the two edges of the sheet were precisely aligned to create a square groove joint with a gap of less than 0.1 mm. Laser welding started from one end of the paired line and extended to the other end, creating a longitudinal weld bead. After welding, some test samples were selected from the silver-white welded drums that had no visible defects. All joint specimens were cut from the welded samples using a wire EDM machine.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Metallographic analysis\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAfter grinding with successive grades of abrasive papers up to 2000 grit and then mechanically polished to a mirror finish using 2.5 \u0026micro;m diamond pastes, the specimens designated for metallographic analysis were subjected to ultrasonic cleaning to remove surface impurities. Subsequently, they were immersed in a ferric chloride solution (FeCl\u003csub\u003e3\u003c/sub\u003e: HCl\u0026thinsp;=\u0026thinsp;10 g: 100 mL) for approximately 15 seconds. Following this, each specimen was thoroughly rinsed with anhydrous ethanol and swiftly dried using a cold air stream. Finally, optical microscopy was employed to examine the physical microstructures and phases.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Immersion tests\u003c/h2\u003e\u003cp\u003eThe ASTM G48-11 standard was used to test the pitting corrosion resistance of LBW joints. To minimize the influence of residual stresses induced by cutting, the edges of the specimens were ground and polished, while the face and root surfaces were retained in their original condition. The specimens were then cleaned using ultrasonic cleaning and absolute alcohol. After measuring their dimensions, the specimens were placed in a drying oven for 24 hours and weighed with a precision of 0.0001 g. Both the base metal and weld specimens were immersed in a 6% (wt.) FeCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO solution for 24 hours at room temperature and at 35\u0026deg;C, respectively. After immersion, the items were cleansed, dried, and then reweighed to determine the amount of weight lost.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 IGC tests\u003c/h2\u003e\u003cp\u003eIntergranular corrosion (IGC) tests for the joints and BM were conducted in line with the ASTM A763-15 standard.\u003c/p\u003e\u003cp\u003eThe oxalic acid etch test was carried out following the procedure outlined in Practice W. The specimens, serving as the anodes, were etched at a current density of 1 A cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e for 90 seconds in a 10% oxalic acid solution. At the same time, a stainless steel sheet was used as the cathode. After etching, the specimen surfaces were examined for IGC using an optical microscope. The etched structures are classified as step, dual, and ditch structures. The presence of one or more grains completely surrounded by ditches indicates IGC.\u003c/p\u003e\u003cp\u003eThe ferric sulfate-sulfuric acid test was conducted in accordance with Practice X. Initially, distilled water, sulfuric acid, and ferric sulfate were carefully added into an Erlenmeyer flask. The condenser and the cooling water were then connected to the flask. The solution was boiled to fully dissolve the solid. The specimen was then immersed in the boiling solution for 24 hours. Subsequent to immersion, the samples were evaluated for microscopic examination.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Electrochemical tests\u003c/h2\u003e\u003cp\u003eThe CHI660E electrochemical workstation (Shanghai Chenhua Co., Ltd) was instrumental in conducting a variety of electrochemical tests. These tests included the double loop electrochemical potentiokinetic reactivation (DL-EPR) test, potentiodynamic polarization test, and electrochemical impedance spectroscopy (EIS) test. A three-electrode cell configuration was employed, with the specimen serving as the working electrode, the platinum electrode as the counter electrode, and the saturated calomel electrode (SCE) as the reference electrode. To ensure the reliability of the results, each electrochemical test was conducted at least three times. The data obtained from these tests was interpreted based on equivalent electrical circuits using CS Studio 5.\u003c/p\u003e\u003cp\u003ePrior to testing, the specimens were encapsulated in epoxy resin and connected with wires. All specimens were polished to achieve a mirror-finished surface with an exposed area of 1 cm\u003csup\u003e2\u003c/sup\u003e. As the HAZ was too narrow to be separated from FZ, the specimens to be tested are pure BM and welded joints which contain FZ, HAZ and BM.\u003c/p\u003e\u003cp\u003eThe solution used in DL-EPR was prepared by dissolving 0.05 mol/L H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and 0.0001 mol/L KSCN in distilled water at 25\u0026deg;C. The specimens were first cathodically polarized at -700 mV (vs. SCE) to remove any existing surface oxides. Then, they were exposed to an open circuit potential (OCP) for a sufficient duration until the rate of potential change was less than 2 mV/h. The specimens were anodically polarized into the passive region from \u0026minus;\u0026thinsp;600 mV to 200 mV at a rate of 3 mV/s, showing an activation current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e). The scan direction was then reversed to the initial potential at a rate of 1.67 mV/s, displaying a reactivation current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e). The susceptibility to IGC can be quantified by the \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e value, calculated as \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e = \u003cem\u003eI\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e\u0026times;100%. A higher \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e value indicates a higher susceptibility to IGC.\u003c/p\u003e\u003cp\u003eIn the potentiodynamic polarization tests, the exposed area of the specimens was limited to 1 cm\u003csup\u003e2\u003c/sup\u003e. First, a 180-minute open circuit potential test was conducted to ensure the stability of the system. The tests were performed in a 3.5% NaCl solution, starting from-1.2V SCE to 0.5 V SCE at a scanning rate of 0.167 mV/s. Following a stabilization period at open circuit potential until the dummy cell potential is 0 V versus the open circuit potential, EIS tests were carried out using 5 mV AC signals across a frequency range of 100 kHz to 0.01 Hz. Similar to the potentiodynamic tests, the EIS tests were also conducted in a 3.5% NaCl solution.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Microstructure\u003c/h2\u003e\u003cp\u003eThe cross-sectional profile and microstructural characteristics of the welded joint are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The weld exhibits full penetration, resulting in the formation of an FZ that resembles a distorted cup. Within the FZ, coarse columnar grains grow from the fusion boundaries on both sides and converge toward the center of the weld pool, ultimately meeting at the centerline of the weld bead. The high travel speed and intense heat input during the welding process lead to a considerable reduction in the size of the HAZ, which makes it challenging to distinguish the boundaries between the HAZ and the FZ. Furthermore, the boundaries between the HAZ and the BM are indistinct due to the similar grain sizes in both areas. The rapid cooling rate experienced on both the face and root sides of the weld facilitates the formation of fine equiaxed grains at the centerlines of these surfaces, primarily through heterogeneous nucleation. Nucleation substrates for the formation of new grains within the weld pool are phases of chemical compounds containing titanium and Nb, which have high melting points. The grains in the HAZ and BM exhibit identical shapes and sizes, indicating that the laser power had no significant impact on them.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Pitting corrosion\u003c/h2\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1 Solution immersion\u003c/h2\u003e\u003cp\u003eAfter a 24-hours of immersion in a ferritic chloride solution at 35\u0026deg;C, the morphology on both the face and root sides of a specimen is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. A notable disparity in the number, size, and distribution of pits between the two sides has been observed. It is clear that more pits are formed on the face side than on the root side. On the face side, there is a higher incidence of pits, with larger corrosion pits predominantly forming in the BM rather than in the FZ. These pits are characteristically aligned parallel to the fusion boundary. On the root side, the FZ exhibits a greater density of pits compared to the BM. Moreover, the pits on the root side are of a smaller size.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe regular distribution of pits in the BM, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a), can be attributed to microstructural alterations caused by the concentrated heat input during welding. The preferential corrosion near the fusion boundary indicates that the integrity of the passive film has been compromised, suggesting the emergence of a chromium-depleted zone in this area. The face side of the weld demonstrates a more pronounced susceptibility to pitting attack compared to the root side. This observation suggests that the laser heating process affects the structures of both the welded joint and the adjacent BM, impeding the ability of the passive film to resist pitting corrosion. Furthermore, because the root side demonstrates greater resistance to pitting corrosion, it is less impacted by the heat generated from the laser compared to the face side. From this point, the HAZ in a laser-welded FSS joint is not as narrow as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In fact, it extends beyond the region where pits appear parallel to the fusion boundaries.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the mass loss rates of both the BM and the welded joint following the immersion test. At room temperature, the BM displays a mass loss rate of 58 mg m\u003csup\u003e-2\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e, indicative of its superior resistance to pitting corrosion compared to the welded joint. The pattern is consistently replicated at 35\u0026deg;C. Conversely, the welded joint exhibits a worse performance in pitting corrosion, with a mass loss rate of 162 mg m\u003csup\u003e-2\u003c/sup\u003e h\u003csup\u003e-1\u003c/sup\u003e. Across all temperature, the mass loss rate of the BM is consistently lower than that of the welded joint, suggesting a reduction in the pitting corrosion resistance after welding. Most notably, since the mass loss rate of the specimen at room temperature is significantly lower than that at 35\u0026deg;C, the pitting resistance of the specimen diminishes as the temperature increases. This effect is more pronounced in the welded joint, where the rate of mass loss escalates more rapidly than in the BM with rising temperature. Therefore, it can be concluded that the pitting resistance of laser-welded B430LNT FSS joints is compromised after welding, and the corrosion rate escalates with an increase in temperature.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2 Potentiodynamic polarization curves\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) shows the OCP (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eop\u003c/sub\u003e) results of BM and welded joint. The essentially constant OCPs over 180 minutes, during which the value of the BM exceeds that of the welded joint, indicate that the system is thermodynamically stable. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b) illustrates the potentiodynamic polarization curves of the welded joint and BM in a 3.5% NaCl solution, while Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c) shows the corrosion potentials (\u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e) and corrosion currents (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e) of BM and welded joint. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e enumerates the specific electrochemical polarization parameters that were fitted by the extrapolation of the Tafel lines.\u003c/p\u003e\u003cp\u003e\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\u003eElectrochemical polarization parameters\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecimens\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e(V)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecorr\u003c/em\u003e\u003c/sub\u003e(\u0026micro;A/cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eE\u003c/em\u003e\u003csub\u003epit\u003c/sub\u003e(V)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003csub\u003eR\u003c/sub\u003e(mm/a)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e (kΩ\u0026bull;cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e-0.229\u0026thinsp;\u0026plusmn;\u0026thinsp;0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e0.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0.044\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.004\u0026thinsp;\u0026plusmn;\u0026thinsp;0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e\u003cp\u003e18.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWelded joint\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e-0.327\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1.95\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e-0.057\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.063\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e\u003cp\u003e16.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\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\u003ePitting corrosion of ferritic stainless steel can be characterized by three distinct stages: initiation, metastable propagation, and stable propagation. Pitting corrosion typically initiates in non-homogeneous areas, where the local breakdown passive films occur. The abrupt failure of the protective film allows the exchange of electrolytes with acidic electrolytes within the pits. This exchange restores the pH to its original level, thereby facilitating the spontaneous repassivation of the steel. This process is commonly known as metastable pitting growth. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e indicates that the polarization curve of the BM exhibits a more pronounced metastable pitting potential range compared to that of the welded joint.\u003c/p\u003e\u003cp\u003eThe critical pitting potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003epit\u003c/sub\u003e) is identified by an inflection point on the polarization curve. It is represented the lowest positive potential at which pits do not form, and the potential above which stable pits nucleate and grow. The \u003cem\u003eE\u003c/em\u003e\u003csub\u003epit\u003c/sub\u003e values for the BM and welded joint are 0.044 V and \u0026minus;\u0026thinsp;0.057 V, respectively, indicating that BM possesses greater resistance to pitting. The \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e reflects the thermodynamic corrosion tendency of materials \u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. As indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b) and (c), the \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e of the BM at -0.229 V is higher than that of the welded joint at -0.327 V. The welded joint exhibited higher current densities in the potential range associated with passivity, indicating inferior corrosion resistance compared to the base metal. As indicated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, both the polarization resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e) and the annual corrosion rate (\u003cem\u003eC\u003c/em\u003e\u003csub\u003eR\u003c/sub\u003e) of BM are greater than those of the welded joint, suggesting a decrease in pitting corrosion resistance following the welding process.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Intergranular corrosion\u003c/h2\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.3.1 Oxalic acid etch test\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e displays the surface morphology of the welded joint after etching with oxalic acid. The microstructure has revealed the formation of oriented columnar grains in the FZ, while the BM retains its equiaxed grain structure. Both columnar and equiaxed grains exhibit signs of IGC along grain boundaries during the etching process. A higher density of ditches is observed in certain grain boundaries within the FZ compared to the BM. Some fine equiaxed grains at the center of the FZ are completely encircled by ditches, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a). Within the indistinct HAZ, where grain sizes are similar to those in BM, the occurrence of IGC is minimal, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (b). Notably, no IGC is observed in the BM and HAZ. In summary, the FZ exhibits a greater susceptibility to sensitization compared to the HAZ in the laser-welded joints of B430LNT FSS sheets.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.3.2 Ferric sulfate-sulfuric acid test\u003c/h2\u003e\u003cp\u003eFollowing the ferric sulfate-sulfuric acid test, the surface morphology of a joint specimen is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The complete morphology of HAZ has been revealed. In a broad sense, the HAZ extends to areas where IGC does not occur. The FZ has an average width of approximately 300 \u0026micro;m, while the HAZ spans an average width of about 100 \u0026micro;m. IGC is observed across the FZ and HAZ, but it predominantly affects the FZ, with minimal grain boundary corrosion noted in the HAZ. In contrast, the BM exhibits the highest level of resistance to IGC within the joint structure.\u003c/p\u003e\u003cp\u003eFigure 8 (a) reveals the grain boundaries in the FZ, particularly along the centerline of the weld, as highlighted by the chemical immersion process. Significant undissolved precipitates are exposed along these grain boundaries, as shown in Fig.\u0026nbsp;8 (b). The body-centered cubic (bcc) lattice of FSS has a lower solid solubility of interstitial atoms, such as C and N, compared to the face-centered cubic (fcc) lattice. Therefore, the diffusion of these elements within the grains is accelerated under the thermal cycling conditions caused by LBW. This acceleration contributes to the formation of precipitates, resulting in pronounced IGC in the FZ.\u003c/p\u003e\u003cp\u003eDue to the concentrated heat input of the laser and the rapid cooling of the sheet joints, grain coarsening in the HAZ is suppressed, resulting in a smaller grain size compared to the FZ. Moreover, fewer particles precipitate along the grain boundaries in the HAZ, leading to only a mild degree of IGC in this area of the laser-welded joint. Therefore, it is deduced that the FZ shows the highest susceptibility to IGC within the joint.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e presents the results of the EDS analysis conducted on the surface of a joint specimen after corrosion, with a focus on the distribution of key elements across the grain structure. Despite the corrosion, fine precipitates are still visible along the grain boundaries. Notably, C and N atoms are found to aggregate along these boundaries, while Cr atoms are noticeably absent in the areas of corrosion pits. This observation suggests that particles enriched with carbon and nitrogen segregate along the grain boundaries after the welding process. It is possible that some of the N content could have come from the shielding gas used during welding. The reduced concentration of Cr atoms at the grain boundaries weakens the ability to maintain the formation of passive films, thus promoting the occurrence of IGC in these regions. Meanwhile, Ti, Nb, and Si exhibit a uniform distribution across the examined area, indicating that their distribution remains unaffected by the thermal cycling experienced during welding.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe separated Nb on the steel surface can stabilize the passive film of the stainless steel and increase the thickness of the passive film of the steels \u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. This film can hinder the breakdown of the matrix in hydrochloric and sulfuric acid solutions. In a sulfuric acid environment, Nb can assist in the formation of an iron oxide film, thereby increasing the thickness and density of the protective layer. However, Nb exhibits a stronger affinity for C and N compared to Cr. During the welding process, Nb atoms tend to bond with C and N, leading to their precipitation at grain boundaries. The formation of Nb(C, N) precipitates creates a potential difference between these particles and the substrate, which can lead to preferential corrosion in areas with concentrated precipitates, ultimately resulting in the formation of pits. Consequently, Ti and Nb are less effective in enhancing the corrosion resistance of laser-welded joints in FSS compared to their impact in BM.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure 10 displays the results of the SEM and EDS analyses conducted on the precipitates found at the grain boundaries in the FZ of B430LNT FSS after laser welding. The analysis revealed the presence of chromium and titanium carbonitrides at these grain boundaries, while niobium precipitates were notably absent. The absence of niobium precipitates could be attributed to their dissolution at the elevated temperatures experienced during welding. In comparison to the Nb content, the Cr content in B430LNT FSS is much higher, resulting in the preferential precipitation of chromium carbonitrides at the grain boundaries. This phenomenon results in the formation of chromium-depleted zones, which subsequently promote IGC.\u003c/p\u003e\u003cp\u003eFurthermore, the presence of titanium precipitates at the grain boundaries can negatively impact the stability of the adjacent passivation film. These precipitates can generate a potential difference between the grain boundary and the substrate, resulting in preferential dissolution. This process further exacerbates the occurrence of IGC, making the welded joints more susceptible to this type of corrosion.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.4 DL-EPR\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e11\u003c/span\u003e illustrates the results of the DL-EPR experiments, focusing on the reactivation current density (\u003cem\u003eI\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) to the activation current density (\u003cem\u003eI\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e) of the specimens. Generally, the ratio (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e) of \u003cem\u003eI\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e to \u003cem\u003eI\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e indicates the degree of sensitization in a specimen.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a), there is no significant increase in the \u003cem\u003eI\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e value for the welded joint. Since it is difficult to separate an entire welded joint from its BM due to the indistinct boundaries between the BM and HAZ, the welded joint sample unavoidably contains a portion of the BM, influencing the experimental results. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e11\u003c/span\u003e (b), the calculated \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e values of the BM and welded joint are 0.47% and 1.13%, respectively. These findings suggest that the welded joint shows some level of sensitization after laser welding. It is important to note, however, that the \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e value can be directly influenced by various factors, such as the experimental temperature and the concentration of the solution used \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e. Given these influencing factors, making direct comparisons between the \u003cem\u003eR\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e values of the BM and the laser-welded joints may not provide completely accurate insights into their relative sensitization levels.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e12\u003c/span\u003e(a) shows the microstructure of the BM after the DL-EPR test. This microstructure is characterized by a dense arrangement of small equiaxed grains, typically formed during the annealing process. Notably, there is an absence of significant IGC at the grain boundaries, indicating the inherent corrosion resistance of the BM. In contrast, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b) depicts the microstructure of the FZ. This area is distinguished by the presence of coarse grains, which are a direct result of the welding process. These grains are scattered across the visual field and are accompanied by severe IGC at their boundaries. The observed IGC within the FZ highlights its increased susceptibility to corrosion compared to the BM.\u003c/p\u003e\u003cp\u003eThe results collectively suggest that the laser welding process disrupts the effectiveness of the stabilizing agents added to the steel. Consequently, the corrosion resistance of the welded joints shows a marked deterioration. The decline in corrosion performance is primarily attributed to the variations in the microstructure induced by the welding process.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.5 EIS tests\u003c/h2\u003e\u003cp\u003eEIS was employed to further examine the effect of laser welding on the passive film of FSS. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e13\u003c/span\u003e presents the Nyquist and Bode plots for both the BM and the welded joint at 25\u0026deg;C in a 3.5 wt% NaCl solution. In the Nyquist plots, two incomplete capacitive semicircles are evident, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a). The polarization resistance can be indirectly inferred from the diameter of the semicircle \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. The diameter of the semicircle arc is correlated with the corrosion resistance of the passive film \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e. It is evident from Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a) that the semi-arc diameter of the welded joint is smaller than that of the BM, indicating a lower polarization resistance and reduced corrosion resistance. The Bode plots illustrate the impedance modulus value and phase angle at various frequencies. In the low-frequency range, the logarithmic value of |Z| for BM is higher, indicating greater polarization resistance \u003csup\u003e[\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. The impedance model at low frequencies aligns with the capacitive arc radius law in the Nyquist plots. Additionally, in the low-frequency domain, the phase angle values of the BM exceed those of the welded joint. It is well established that the welded joint with a lower impedance value and a more positive phase angle exhibits poorer corrosion resistance compared to the BM.\u003c/p\u003e\u003cp\u003eAn equivalent circuit model was utilized to represent the electrochemical system and to fit the impedance data obtained from the EIS measurements, as is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e13\u003c/span\u003e(a). In this model, \u003cem\u003eR\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e reprents the electrolyte resistance, \u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e represents the passive film resistance, and \u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e represents the charge transfer resistance. In addition, \u003cem\u003eQ\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e represents the capacitance of the passive film, while \u003cem\u003eQ\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e represents the capacitance of the double layer. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e provides the detailed circuit parameter values acquired after fitting the experimental EIS data with the equivalent circuit model \u003cem\u003eR\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e(\u003cem\u003eQ\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e(\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e(\u003cem\u003eQ\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e))), and the chi-squared errors (χ\u003csup\u003e2\u003c/sup\u003e) in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e validate the equivalent circuit model for the passive film system. Due to the non-homogeneity of the FSS surface, the capacitance measured for the passivated film is likely to deviate from the ideal capacitance. Therefore, the constant phase element \u003cem\u003eQ\u003c/em\u003e is used to replace the capacitor \u003cem\u003eC\u003c/em\u003e during fitting. The impedance of \u003cem\u003eQ\u003c/em\u003e is represented in the following form:\u003c/p\u003e\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"349\" height=\"50\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u003cem\u003eQ\u003c/em\u003e is the constant phase element of the electrode, \u003cem\u003ej\u003c/em\u003e is the imaginary unit, \u003cem\u003e\u0026omega;\u003c/em\u003e represents the angular frequency, and \u003cem\u003en\u003c/em\u003e is the constant phase index \u003csup\u003e[40]\u003c/sup\u003e. Typically, \u003cem\u003en\u003c/em\u003e has a value between 0 and 1. If \u003cem\u003en\u003c/em\u003e is close to 1, \u003cem\u003eQ\u003c/em\u003e represents the ideal capacitance. The total impedance \u003cem\u003eZ\u003c/em\u003e(\u0026omega;) can be evaluated using the following relation.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" width=\"421\" height=\"83\"\u003e\u003c/p\u003e\u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the welded joint exhibits relatively low \u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e values, indicating that laser welding may compromise the corrosion resistance. In contrast, the higher \u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e values for the BM suggest limited migration of electrons and/or ions across the passive film and interface, which implies better corrosion resistance for the BM \u003csup\u003e[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/sup\u003e. The parameters \u003cem\u003en\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e and \u003cem\u003en\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e represent the dispersion coefficients of \u003cem\u003eQ\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e, respectively. Since \u003cem\u003en\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e deviates significantly from 1 compared to \u003cem\u003en\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e, the double-layer capacitance is not ideal. Additionally, the \u003cem\u003eQ\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e values for the BM are greater than those for the welded joint. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e also indicates that the electrolyte resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e) of the welded joint slightly decreases compared to that of the BM. These findings suggest that the protective performance of the passivation film in the welded joint is inferior to that in the BM.\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\u003eEquivalent circuit parameters for the EIS of the BM and Welded joint\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecimens\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e (Ω.cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e (Ω∙cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e (\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e.cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003csub\u003ef\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e (Ω∙cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003edl\u003c/em\u003e\u003c/sub\u003e (\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003eF.cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eχ\u003csup\u003e2\u003c/sup\u003e (\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e12.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e7.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e4.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e\u003cp\u003e3.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e\u003cp\u003e1.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e\u003cp\u003e0.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c9\"\u003e\u003cp\u003e2.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWelded joint\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e10.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e3.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e5.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e0.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e\u003cp\u003e1.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e\u003cp\u003e3.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c8\"\u003e\u003cp\u003e0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c9\"\u003e\u003cp\u003e2.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eBased on the characterization of microstructure, electrochemical testing, corrosion morphology, and elemental scanning analysis, Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e14\u003c/span\u003e schematically illustrates the changes in element distribution and the formation of precipitates during the laser welding process, as well as the corresponding decrease in corrosion resistance of the joint. In this figure, hexagonal symbols represent the grains in the matrix, while geometric shapes in various colors denote different elements and their compounds. In particular, the variation in colors along the grain boundaries indicates the integrity of the passivation film.\u003c/p\u003e\u003cp\u003eAfter annealing, the initial distribution of elements and compounds in BM grains is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e14\u003c/span\u003e(a). Both niobium and titanium carbonitrides are formed and evenly distributed throughout the grains and their boundaries. The absence of these carbonitrides on the surfaces of the BM correlates with a reduced risk of pitting corrosion \u003csup\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThe welding process induces significant changes in the microstructure. During the melting stage, specific compounds in the welding zone decompose at elevated temperatures. Nitrogen from the shielding gas permeates the weld pool both physically and chemically. The high temperature generated by the laser beam creates conditions that favor the formation of carbonitrides within the weld pool \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e. Meanwhile, certain metallic and nonmetallic elements evaporate due to the high temperature. All elements, with the exception of certain carbonitrides, dissolve in the liquid metal \u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eDuring the cooling stage, Ti(C,N) and Nb(C,N) particles with high melting points are formed in the weld pool owing to their strong affinity for C and N. These solid particles act as substrates for crystal nuclei and promote heterogeneous nucleation. Subsequently, numerous equiaxed grains develop at the center of the FZ. The relatively small average grain size facilitates the diffusion of Cr, Ti, and Nb to the grain boundaries. Additionally, the solid solubility of interstitial elements such as C and N in the bcc lattice of FSS decreases after solidification. This reduction in solubility increases the diffusion of solute atoms \u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e. Although the rapid cooling rate may impede the precipitation of secondary phases, which is beneficial for improving corrosion resistance \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e, metallic carbonitrides do precipitate along these grain boundaries, as shown in Fig.\u0026nbsp;10. These phenomena account for the primary distribution of carbonitrides at the centers and edges of the grains.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe intentional incorporation of Ti and Nb does increase their competitive binding to N and C in comparison to Cr. However, chromium carbonitrides continue to form at the grain boundaries in LBW due to the high chromium content, elevated welding temperatures, and nitrogen absorption. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e14\u003c/span\u003e(c) shows that chromium-depleted zones develop as a result of the precipitation of chromium carbonitrides after welding, even in the presence of Ti and Nb [16, 48]. Consequently, laser-welded FSS joints are more susceptible to IGC.\u003c/p\u003e\u003cp\u003eFurthermore, chromium-deficient regions and carbonitrides at the grain boundaries hinder the continuous formation of a passive film in the welded joints. The presence of titanium carbonitrides can create an electric potential difference with the matrix, leading to instability and a lack of integrity in the passive film, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e14\u003c/span\u003e(d). Therefore, IGC and pitting corrosion occur at the grain boundaries, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn this study, the effects of laser welding on the pitting and intergranular corrosion resistance of thin plates of ferritic stainless steel with stabilized elements niobium and titanium were investigated. An in-depth analysis led to the following conclusions.\u003c/p\u003e\u003cp\u003e(1) Pitting is likely to occur on the face side of laser-welded FSS joints, specifically in HAZ that runs parallel to the fusion line and along the centerline of FZ. The pitting corrosion is primarily due to the concentrated heat input, which leads to the formation of chromium-depleted zone in the HAZ, thereby compromising the ability of surface layers to sustain a protective passive film. Since the root side exhibits greater resistance to pitting corrosion, it is less impacted by the laser heat.\u003c/p\u003e\u003cp\u003e(2) The weight loss measurements and the potentiodynamic polarization curves show that the pitting resistance of laser-welded B430LNT FSS joints is compromised. The corrosion rate of welded joints increases with an increase in temperature. The decrease of both \u003cem\u003eE\u003c/em\u003e\u003csub\u003epit\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003ecorr\u003c/sub\u003e in welded joints implies a reduction in pitting resistance after welding.\u003c/p\u003e\u003cp\u003e(3) Results from the oxalic acid etch test, the ferric sulfate-sulfuric acid test, and DL-EPR curves reveal that the welded joint is more prone to IGC, in contrast to the BM. IGC takes place predominately at grain boundaries in FZ, and secondarily at grain boundaries in HAZ. Precipitates formed along the grain boundaries during the LBW contribute to the IGC in weld joints.\u003c/p\u003e\u003cp\u003e(4) Despite the addition of Ti and Nb, Cr (C, N) still precipitates at grain boundaries in welded joints. The Cr-rich compounds may result from the high Cr content in the metal matrix and nitrogen absorption, which leads to chromium-depleted zones in neighboring grains. The precipitation of carbonitride at the grain boundary creates an electrochemical potential difference, resulting in electrochemical corrosion.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting Interests\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis project is financially supported by the China-Ukraine Government Science and Technology Exchange Project (2022\u0026ndash;2023) under name of Pengcheng Zhao.\u003c/p\u003e\u003ch2\u003eAuthors Contributions\u003c/h2\u003e\u003cp\u003eTian Gao conducted the experiments and drafted the manuscript. Mingmei Tang collected and analyzed the corrosion data. Pengcheng Zhao was responsible for the methodology and investigation. Guoshuai Yan performed the metallurgical analysis. Lulu Wang contributed to the editing of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThis work was supported by China-Ukraine Government Science and Technology Exchange Projects (2022\u0026ndash;2023) under the name of Pengcheng Zhao. The authors would like to thank Mr. Hongtai Liu and Yazhou Xu for their assistance in the laser welding experiments. One of our authors, Tian Gao, would appreciate Mr. Zhenhui Zhao for his advice in preparing the equipment.\u003c/p\u003e\u003ch2\u003eData Availability Statement\u003c/h2\u003e\u003cp\u003eThe data are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZheng C, Ke J-H, Maloy SA, Kaoumi D. Correlation of in-situ transmission electron microscopy and microchemistry analysis of radiation-induced precipitation and segregation in ion irradiated advanced ferritic/martensitic steels. 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Journal of Materials Science \u0026amp; Technology 2019;35:1787-1796. https://doi.org/10.1016/j.jmst.2019.03.021.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"B430LNT ferritic stainless steel, corrosion resistance, laser-welded joint, microstructure, IGC, pitting corrosion","lastPublishedDoi":"10.21203/rs.3.rs-7005471/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7005471/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe corrosion resistance of laser-welded joints in ultra-pure B430LNT ferritic stainless-steel sheets stabilized with titanium and niobium was investigated in this study. The pitting resistance of the welded joints was evaluated by conducting immersion and potentiodynamic polarization tests. The intergranular corrosion resistance was assessed by chemical acid etching tests and double-loop electrochemical potentiokinetic reactivation methods. The passive films on the surfaces of welded joints were analyzed by using electrochemical impedance spectroscopy tests. The results indicate that the microstructure of welded joints are as-welded, consists of large columnar and small equiaxed grains. Pitting corrosion occurs in the heat-affected zone and fusion zone, with the majority of pits in the heat-affected zone being parallel to the fusion line. The base metal demonstrates better resistance to intergranular corrosion compared to the fusion zone, and the stability of the passive films at the base metal is greater than that of the welded joint. The Ti and Nb in welded joints do not work as effectively as they do in the base metal. The high content of chromium in the metal matrix and absorption of nitrogen from the shielding gas promote the formation of chromium carbonitrides at grain boundaries, leading to the creation of chromium-depleted zones. The formation of Cr and Ti carbonitrides near the surfaces of welded joints decreases the stability of the passive films and promotes pitting corrosion. The various factors render the welded joint area susceptible to corrosion.\u003c/p\u003e","manuscriptTitle":"The corrosion resistance of laser-welded joints made of Ti and Nb stabilized B430LNT ultrapure ferritic stainless-steel sheets","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-14 10:17:49","doi":"10.21203/rs.3.rs-7005471/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-07-14T03:40:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-10T07:20:53+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2025-07-10T07:00:11+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-08T15:26:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2025-07-06T08:49:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"955d67ff-ae9d-421b-89b4-82dc015b55de","owner":[],"postedDate":"July 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T06:19:58+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-14 10:17:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7005471","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7005471","identity":"rs-7005471","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}