Microstructural and Mechanical Behavior of Welds in Partially Transformed TRIP 800 Steel Produced by Friction Stir Spot Welding (FSSW)

Microstructural and Mechanical Behavior of Welds in Partially Transformed TRIP 800 Steel Produced by Friction Stir Spot Welding (FSSW) | 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 Microstructural and Mechanical Behavior of Welds in Partially Transformed TRIP 800 Steel Produced by Friction Stir Spot Welding (FSSW) Henderson Soares Madureira, Carlos Alberto Carvalho Castro Castro, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4202425/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The industry’s pursuit of clean technologies and materials amidst growing concerns about climate change underscores the significance of innovative welding processes. The utilization of TRIP 800 steel, renowned for its transformation-induced plasticity, highlights the endeavor towards enhancing energy efficiency and safety in the automotive sector. Nevertheless, welding this material poses significant challenges, particularly in the formation of martensitic regions in the weld zone, potentially resulting in reduced ductility and increased brittleness. Additionally, the thermal cycle involved in the welding process may induce unfavorable microstructural changes, affecting the overall integrity of the welded joint. Despite these challenges, FSSW emerges as a promising alternative to traditional welding processes, offering advantages such as reduced energy consumption and enhanced mechanical properties. This study aimed to investigate welds in TRIP 800 steel sheets through the Friction Stir Spot Welding (FSSW) process after deformation, thereby reflecting broader applications beyond vehicle manufacturing. The interaction of factors, including time and rotation speed, was examined at various levels for microstructural characterization, tensile and microhardness tests, showcasing the versatility and potential of the FSSW process. The analysis of welded joints revealed distinct regions such as the stir zone, thermomechanically affected zone, thermally affected zone, and base metal, illustrating the complexity and precision of modern welding techniques. Notably, the study delved into the microstructures of the affected zones, elucidating their pivotal role in influencing mechanical behavior under load conditions until failure. This investigation contributes to the ongoing quest for innovative solutions in vehicle manufacturing, emphasizing the importance of understanding welding processes and material properties in achieving sustainability and performance goals. Friction welding TRIP steel Microstructure Mechanical properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 1. INTRODUCTION The escalating concern regarding climate change has been a catalyst for the industry’s endeavors to adopt cleaner technologies and materials. Within this framework, a significant challenge confronting the automotive sector is the enhancement of energy efficiency while simultaneously meeting progressively restrict requirements for fuel consumption and safety standards. To address this demand, there is an increasing reliance on materials distinguished by lower thickness yet greater strength and toughness. Historically, until the 1980s, the mainly steels used in vehicle manufacturing featured a yield strength of 325 MPa. However, numerous applications have since shifted towards the use of Advanced High-Strength Steels (AHSS), which are characterized by yield strengths over than 780 MPa and, in some instances, reaching 1000 MPa. This transition has resulted in the production of considerably safer vehicles, with a final weight up to 35% lower. Notably, among these advanced steels are Transformation Induced Plasticity (TRIP) steels [ 1 ]. The TRIP effect involves a phase change from metastable austenite to martensite when deformation is applied, promoting grain reorientation and self-accommodation, also known as the Greenwood-Johnson effect and the Magee effect [ 2 ]. Typically, these low-alloy steels have a ferritic matrix structure composed of a fraction of 10 to 15% retained austenite with small inclusions at the grain boundaries. The use of TRIP steels is associated with excellent formability and high mechanical strength obtained after stamping operations combined with toughness. However, conventional welding methods like Resistance Spot Welding (RSW) may result in the formation of a fusion zone and a heated affected zone with a high volumetric fraction of martensite, which is brittle. To mitigate such effects, post-welding heat treatments are considered; however, this leads to a significant increase in manufacturing costs. Friction Stir Welding (FSW) is a solid-state welding technique that initially emerged to weld non-ferrous materials but soon expanded to other alloys such as aluminum, magnesium, and copper [ 3 , 4 , 5 ]. Thermal input in FSW is generated by converting kinetic energy into thermal energy through friction between the shoulder, pin, and workpiece surface. The pin, which can have complex geometries, needs to be a few millimeters shorter than the sum of the thickness of the overlapped sheets or the thickness of the sheets in the case of butt welds [ 6 , 7 ]. Friction Stir Spot Welding (FSSW) is a variation of the FSW process, differing primarily in its localized application, targeting specific spot areas for welding. It offers an interesting alternative as it can minimize the effects of the welding thermal cycle and demonstrate good efficiency with lower energy consumption, combined with the absence of consumables such as shielding gases, fluxes, or filler material. The process requires high torque and forces necessary to mix the plasticized material and the tool, which must withstand these forces [ 8 , 9 , 7 , 10 ]. The most important parameters in the production of this type of weld are the mixing time, followed by rotation speed and penetration depth. The FSSW process, which starts with the predetermined rotation, initiates by applying normal force to the joint to be produced. The heated material is plasticized and stir, and the process continues for a predetermined time, followed by tool retraction [ 11 , 12 , 13 , 14 ]. Therefore, the study scope was to produce welds in TRIP 800 partially transformed, condition frequently met in automotive industry, by FSSW process as a way to understand and overcome the challenges mentioned above. The effect of rotation speed and mixing time in the weld mechanical behaviour and microstructure were investigated. The microstructural changes were related to mechanical properties, i.e., weld shear strength and heat input during processing. 2. MATERIALS AND METHODS In this study, TRIP 800 steel with a thickness of 1.5 mm and a typical chemical composition of C 0.19%; Si 1.65%; Mn 1.64%; Al 0.39%; P 0.16% was utilized. To determine the number of samples, a Central Composite Rotatable Design (CCRD) was employed, incorporating two factors: rotation speed (rpm) denoted as (B), and mixing time (A), each at two levels (2x2), in addition to four axial points (2x2), and the central point. The central point was reiterated five times, resulting in a total of 13 tests, as depicted in Fig. 1 . The preparation of the test specimens involved two stages. Initially, they were cut in the rolling direction and then subjected to a pre-deformation of 10% to promote the microstructural transformation induced by plasticity. For this purpose, an Instron model 5982 universal testing machine was used, along with the Blue Hill3 control and data acquisition system, employing a needle-type extensometer (Instron model 2630 − 106). This alloy is typically welded stamping, i.e., after the plasticity induced transformation phenomenon. The weld test specimens were produced according to the [ 15 ], with dimensions of 30 mm in width and 102 mm in length, cutted in the rolling direction. The sheets overlapping was 50 mm, and the formed weld spot was positioned centrally, as depicted in Fig. 2 The factors interacting in the weld produced by the FSSW process are the rotation speed and mixing time, determined in preliminary tests. The tool pin penetration speed was set between 0.4 mm/s, as proposed in the literature. The samples were fixed in a device manufactured for this purpose, ensuring a perfect alignment and necessary overlap for weld production, according to the [ 15 ]. A machining center, Romi model D800, was used for the FSSW process. Microstructural analysis to evaluate the present constituents/phases was performed using cutting, grinding, and metallographic polishing techniques to avoid the transformation of the present phases, which could lead to misinterpretations. The grinding techniques followed a stepped pattern of grit size (120, 220, 320, 400, 600, and 1200 mesh) with alternating grinding directions [ 16 , 17 , 9 , 18 ]. Subsequently, polishing was done using diamond paste (9, 3, and 1 micron) and chemical etching with a 3% Nital solution. Macrostructural analysis was conducted using a Zeiss STEMI 2000-C stereoscopic microscope equipped with a camera for image acquisition. To identify ferrite, bainite, martensite, and retained austenite, complementary microstructural analyses were performed using a Shimadzu SSX-550 Superscan scanning electron microscope, owing to grain refinement. The tensile test was carried out utilizing an Instron model 5982 universal testing machine with the Blue Hill3 control and data acquisition system. According to the [ 15 ], the deformation rate was set at 17 mm/min. Following the tensile test, the areas were determined by examining the images of the samples using the ImageJ software. The microhardness profile was obtained on the upper sheet, 0.25 mm from the lower side, across the entire section, including the stir zone, thermomechanically affected zone, thermally affected zone, and base metal. Indentations were made using a load of 0.200 Kgf for 10 seconds, with a 0.2 mm step between indentations, ensuring multiple hardness measurements of the matrix in each weld region with a Shimadzu HMV-20 hardness tester. Measurements of the weld regions were analyzed using the Image J. image analysis software. The energy input was indirectly calculated using data from voltage and current values collected with a U1242b multimeter and a U1212 Agilent ammeter at a rate of 10 data points per second at the output of the frequency inverter of the equipment. Data collection began with the start of pin penetration and ended with tool retraction. The energy values inputted into the process considered the rotation speed and mixing time. 3. RESULTS AND DISCUSSION As a solid-state joining process, the primary sources of heat in Friction Stir Spot Welding (FSSW) are the friction between the shoulder and pin of the tool and the material, which are correlated with the tool rotation speed and the plastic deformation the material undergoes. The calculated energy values for the welds produced with various parameter interactions are presented in Table I. TABLE I. Total Energy for Different Parameters Rotation Speed (rpm) Mixing time (s) Energy (kJ) 1435 3 24.2 1600 2 16.9 1600 4 25.6 2000 1.6 22.7 2000 3 25.5 2000 4.4 27.9 2400 2 27.1 2400 4 29.2 2565 3 34.9 The supplied energy was calculated indirectly using Eq. 1, as cited in Eagar (1986) and employed by Khan [ 19 ], as a function of the normal force F, tool positioning X, torque τ, angular velocity ω, and process duration time. The data were collected at the output of the frequency inverter of the machine used. Since the tool does not move, the first part of the equation is disregarded, leaving only the relationship between angular velocity, torque, and time. The data indicates that energy values increased with the increase in rotation and time; however, rotation has a greater influence on the energy input compared to the mixing time. The standardized effects graph of the parameters can be viewed in Fig. 3 , generated using Minitab software. The rotation speed was found to be the most significant parameter. The energy calculations exhibited a normal distribution with an 95% confidence level according to statistical analysis. However, it’s important to note that process losses were not factored in, and the collected energy data from the inverter output might not precisely reflect the actual values. Nonetheless, this consistent method was applied to all samples, ensuring consistency. A response surface showing the probability of generated energy is displayed in Fig. 4 , created using Minitab software. The probability of energy predictability is illustrated in Fig. 5 , created using Minitab software. The values of the welded area and the corresponding shear strength of the welds obtained for various parameter combinations are presented in Table II. The correlation analysis between the energy data and area did not reveal a direct relationship between these variables. Khan, in the experiments with transformable steels, described a similar effect, highlighting the lack of linearity between energy, yield strength, and welded areas, although was observed a larger welded area with the application of higher energy [ 19 ]. In this specific study, the welded area varied around a mean value, making it difficult to identify a clear trend. However, Feng observations suggest that increasing the time in experiments resulted in an expanded bonding region [ 20 ]. Indeed, the nonlinearity observed in this study aligns with the complexity of the welding process and underscores the importance of considering additional factors. One such factor that may influence the formation of the weld region thickness, but has not been evaluated before, is the pressure exerted by the tool. Xie, citing Santella et al., argues that, for the same material, higher pressure can have a significant impact on the strength limit [ 12 ]. The relationship between weld area and shear strength for various rotation speeds and mixing times is depicted in Fig. 6 . The lack of a clear correlation between these variables suggests the potential influence of other factors on the shear strength limit. Remarkably, the weld achieved at a rotation speed of 2000 rpm and 4.4 seconds exhibited unusually the lowest shear strength limit. In this case, the area of the welded region increased compared to the weld obtained at 2000 rpm and 3 seconds. This discrepancy could arise from the formation of different constituents or discontinuities during the process, potentially diminishing both the strength and the effectively welded area. Such conditions might have contributed to the weld’s early failure. When comparing the images, it becomes evident that there is a lack of a consistent fracture pattern, except for the fact that it seems to have originated at a point along the line formed between the sheets. It is noteworthy in this case that such occurrence indicates a partial union or even absence thereof at the outer end of the joint. This failure process traverses the line formed on the lower sheet until reaching the rupture in the stir zone of the upper sheet. The macrographs, which provide a visualization of the fractured surface aspect of the welds after the test, are presented in Fig. 7 and Fig. 8 . The macrographs of the welded specimens revealed distinctive regions whose size and composition varied depending on the parameters employed affected by process energy. Figure 9 presents a typical weld cross-section, delineating the stir zone, thermomechanically affected zone, thermally affected zone, and base metal, as elucidated by [ 20 ] and further classified into sub-regions by [ 21 ]. The microstructural examination specifically targeted the central points within these regions to assess the constituent elements. Additionally, the formation of a discontinuity situated between the welded plates and the coalesced material, as illustrated in Fig. 10 , was observed in all welds. This phenomenon tends to become more visible when the distance, created by the central pin promoting material mixing, increases. The dimensions of it tend to reduce with material diffusion become more effective by heating, which intensifies with the proximity of the central pin. Rotation speed also influences this, as noted by [ 12 ]. Observing the highlighted detail in the figure, can be noted the presence of acute angles on the outer part, formed between the coalesced material that was forced between the plates during the tool pin movement. Under certain processing conditions, as illustrated in the macrograph in Fig. 11 , the presence of cracks was observed starting from the edge of the discontinuity. Internal stresses resulting from welding or external forces can propagate it, potentially leading to the total failure of the weld. This phenomenon is commonly observed in welds with high energy in transformable steels, in which cracks propagate through the mixing zone until complete failure [ 19 ]. The discontinuity formation, indicating a mixing lacking mainly in the external regions where the maximum temperatures are lower, was observed in all welds produced. However, it is more evident in the weld depicted in Fig. 11 , which was produced using 2000 rpm (rotation speed) and 4.4 seconds (mixing time) where a crack appears at the end of the discontinuity located along the mixed and thermomechanically affected zones in the bottom position. The base metal microstructure is illustrated in Fig. 12 showcasing ferrite, martensite, bainite, and retained austenite even after the initial plastic deformation of 10%. The presence of martensite is not inherent to this steel in as-received condition indicating an effective transformation phenomenon induced by plasticity. The martensite fraction observed results from the TRIP effect, leading to a decrease in the fraction of retained austenite. The remaining fraction suggests that the transformation effect can still manifest in this material under stress and deformation. The images captured with SEM at a magnification of 3500 times depicted in Fig. 13 represent the mixed zone of the welds generated by using a mixing time of 3 seconds across three distinct rotation speed levels. Generally, a microstructure predominantly comprising martensite and bainite is discernible. The presence of martensite can be attributed to cooling rates surpassing the critical value during welding cycle, in a region where maximum temperatures reached is higher than those necessary for complete austenitization. Additionally, it is evident that the rise in rotation speed led to an enlargement in the size of the martensite laths. This observation can be linked to the development of larger austenitic grains in processes conducted at higher rotation speeds, which are correlated with increased input energy and, consequently, higher peak temperatures. This effect is consistent with Mazzaferro findings that higher rotation speeds resulted in a decrease in both the quantity and size of bainite grains in similar materials [ 21 ]. As the rotation speed increases, martensite plates tend to enlarge while bainite experiences a reduction in quantity and size. In another hand, images from Fig. 14 obtained using SEM, reveal the impact of mixing time on the constituents at a fixed rotation speed parameter of 2000 rpm. The mixed zone exhibits a refined structure predominantly composed of martensite along with what appears to be bainite. This is consistent with findings in other samples where the presence of martensite is likely attributed to the critical cooling temperature reached after attaining the austenitization temperature. Any austenite that did not undergo martensitic transformation may persist as retained austenite or decompose into bainite. In the sample with a time of 1.6 seconds, the presence of ferrite was restricted and localized at certain grain boundaries, a phenomenon not observed in other samples. Additionally, the size of martensite plates tends to increase with higher energy input in the process, which, in this case, is directly correlated with time. Austenite that has not undergone martensitic transformation may persist in the form of retained austenite or decompose into bainite. The observed martensite plates also tend to be larger with higher energy in the process, which, in this case, is associated with the growth of austenitic grain favored by mixing time increasing. The mixed zone exhibits a refined structure primarily composed of martensite and bainite, which is consistent with earlier observations. The presence of martensite is likely linked to the critical cooling temperature after reaching the austenitization temperature. Austenite that hasn’t undergone martensitic transformation may persist as retained austenite or decompose into bainite. Larger martensite plates are observed with higher energy in the process, likely due to increased growth of austenitic grain facilitated by time and rotation speed. Figure 15 shows the thermomechanically affect zone constituents of the welds produced at rotation speeds of 1435 rpm, 2000 rpm, and 2565 rpm, with a welding time of 3 seconds. The sample with a rotation speed of 1435 rpm exhibits a structure closer to that of the base metal. It is possible that this region did not reach temperatures to promote significant changes in constituents, and the martensite likely resulted from the initial 10% deformation. In the sample produced using 2000 rpm, there was a decrease in the amount of austenite, accompanied by the growth of ferrite grains and an increase in bainite, which is expected from austenite decomposition. The occurrence of retained austenite is also minimal, and existing martensite likely must be related to the initial deformation. The sample with a parameter of 2565 rpm exhibited a martensitic matrix. Alongside martensite, there is an expected bainite constituent, with ferrite occurring in small amounts and the presence of retained austenite is minimal. In these instances, the formation of higher hardness constituents in the thermomechanically affected zone correlated with increased rotation speed. This could be attributed to the higher peak temperatures reached, as noted by Mazzaferro (2008), potentially leading to the attainment of the austenitization temperature. Weld microstructure produced with fixed rotation speed (2000 rpm) but varying in mixing time is presented in Fig. 16 . The weld made with a time of 1.6 seconds demonstrates a reduction in retained austenite within the thermomechanically affected zone compared to the base metal. The presence of martensite is likely due to the initial 10% deformation, with small occurrences of austenite and bainite. In contrast, the weld with 3 seconds mixing time showcases an increase in ferrite grain size and a higher amount of bainite resulting from austenite decomposition when compared to the weld with a 1.6 second. The weld with a mixing time of 4.4 seconds exhibited a martensitic matrix accompanied by what seems to be bainite in smaller proportions. Among all samples, this one displayed the highest martensite content in the thermomechanically affected zone, suggesting extensive austenitization with a longer mixing time. This, coupled with critical cooling rates, facilitated the formation of significant quantities of martensite. The development of internal stresses may have contributed to the crack observed earlier in Fig. 11 . In these instances, the formation of higher hardness constituents in the thermomechanically affected zone was observed with an increase in mixing time. Various parameters influenced the behavior of the weld, leading to alterations in the dimensions of the formed zones and the resulting microstructures. Hardness profiles were obtained through tests performed using a Vickers Hardness tester, and indentations were made to analyze the hardness of the constituents formed in different regions. Although the hardness values in the mixed zone are similar, the size of martensite plates increased with the rotation speed. Additionally, the thermomechanically affected zone exhibited a composition with a higher fraction of microconstituents, such as martensite and bainite, at higher rotation speed values. Lower values allowed the presence of constituents like ferrite and retained austenite, remaining from the base metal. The hardness profile conducted on samples with a base time of 3 seconds and rotation speeds of 1435, 2000, and 2565 rpm is depicted in Fig. 17 , revealing consistent values with the founded mixed zone microstructure. As the rotation speed increased from 1435 to 2565 rpm, hardness values exhibited a slight reduction, a phenomenon also noted by Mazzaferro (2010) [ 22 ]. This reduction could be attributed to the larger size of martensite plates. However, the values, when considered alongside the standard deviation, overlap, hindering a definitive conclusion about the trend. Furthermore, hardness values decrease as one moves away from the mixed zone, a pattern observed by both Feng (2005) and Mazzaferro (2010) [ 20 , 22 ]. It is hypothesized that the transformation of martensite in the mixed zone is linked to the critical cooling rate after reaching temperatures AC1 and AC3 with a high degree of austenitization. The hardness profile depicted in Fig. 18 for samples with a fixed rotation speed of 2000 rpm and varied times (1.6 s, 3 s, and 4.4 s) showed typical hardness expected considering the founded mixed zone microstructure. Comparing the average hardness of mixed zone is observed a slight reduction with a mixed time increasing but the variations are within standard deviation. This behavior must be related to the thermal cycle and the resulted microstructure which presents differences in the martensite laths. In all samples, the thermomechanically affected zone serves as a transition area where hardness values decrease as one moves away from the mixed zone to base metal, as observed in the hardness profile. This can be clearly understood by the microstructure formed in this region. The microstructural variations resulted by rotation speed and mixed time changes also must be observed in the hardness profile. In turn, as expected, the thermally affected zone tends to presents hardness close to the base metal. 4. CONCLUSION In this paper, the effects of the rotation speed and mixing time in friction spot welding of a TRIP 800 steel, after undergoing a plastic deformation of 10%, were investigated. Based on these results and the analyses of the conducted tests, the following conclusions can be drawn: Regarding the energy input in the process, it was observed that the rotation speed is more relevant than the time; It was not possible to establish a linear relationship between the area of the welded region and the energy, nor with other parameters involved in the process. Additionally, the effect of pressure on the welding process was not investigated, which could be considered a topic for future studies; The analysis of the effects of time and rotational speed parameters on the mixed zone reveals that, as the rotation speed increases, there is an increase in martensite plates accompanied by a reduction in the bainite constituent. The significant presence of martensite can be attributed to heating up to the austenitization temperature, correlated with the growth of austenitic grains. These austenitic grains have the potential to transform into martensite when the critical cooling rate is reached, while grains that do not undergo this transformation may remain as retained austenite or decompose into bainite. The analysis of the effects of mixing time and rotation speed parameters on the thermomechanically affected zone showed these factors increase, there is a reduction in ferrite and austenite, accompanied by an increase in the bainite and martesite constituents. The presence of martensite in this case must be related to the pre-deformation of the material and peak temperatures above austenitic transformation. Regarding the microhardness profiles, it can be observed that the graphs presented three distinct regions, with the mixed zone reaching high hardness values consistent with the martensitic microstructure found. The thermomechanically affected zone appears as a transition zone with a decrease in hardness as the distance from the mixing pin increases up to the thermally affected zone, which has hardness similar to that of the base metal; The formation of discontinuities occurred, indicating localized failure in the material joining and likely where the rupture process must initiate. Under specific conditions cracks originated and propagated through the mixed zone. Declarations The authors’ of this manuscript declare that there is no conflict of interests regarding submission and publication of this manuscript. Acknowledgements The authors would like to acknowledge Centro Federal de Educação Tecnológica de Minas Gerais (CEFET- MG). This work was partially supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Brazil (CAPES) - Financing Code 001. References WANG W, ZHANG S, QIAO K, WANG K, PENG P, YANG Q (2019) Microstructure and mechanical properties of friction stir welded joint of TRIP steel, 2020. Editorial board J Mater Sci Technol. doi.org/10.1016/j.jmapro.2020.05.045 REISNER FISHERFD, WERNER G, TANAKA EA, CAILLETAU K, ANTERETTER G (2000) A new view on transformation induced plasticity (TRIP). Int J Plast. doi.org/10.1016/S0749-6419(99)00078-9 SHIN DAVISTA (1987) Observer-Based Adaptive Robust Control of Friction Stir Welding Axial Force. 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In: Departamento de Engenharia de Materiais, Centro Federal de Educac¸a˜o Tecnologica de Minas Gerais - Brasil doi.org/10.1590/S0104-92242009000400002 ROSENDO MAZAFERROCCP, TIER TS, M. A. D.; MAZAFERRO JAE, Silva D (2010) A. M. STROHAECKER T. R. Friction stir spot welding of a trip steel: microstructural characterization/Soldagem a ponto por fricçao e mistura mecânica de um aço trip: caracterização microestrutural. In: Tecnologia em Metalurgia e Materiais Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-4202425","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":290639666,"identity":"ca4bf289-8606-4d96-af5c-5d633242715c","order_by":0,"name":"Henderson Soares Madureira","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5klEQVRIiWNgGAWjYBACAyCWALPYGxgYKsAsHmK18BxgYDgD5hOtRSKBSC3m7L0Hb3zcUydnLvn44YMDFX+i5R14j33Ap8Wy51yy5Yxnh40tZ6cZGxw4Y5C78QBf8gy8DruRYybNc+BA4obbOWzSH9uAWhp4jPH75f4bM+k/B+oSN9w8w/7j4D9itNzgMZNmOMCcuOEGDxvDwQaD3PkMhLScyTG27Dlw2NjgTJqxxIFjxrkbmPmS8Ws5fsbwxo8DdXIGxw8//HCgRi53fnvvYbxasBhCqgYGBvkGkrWMglEwCkbBMAcAyeZQKNSe9U8AAAAASUVORK5CYII=","orcid":"","institution":"Centro Federal de Educacao Tecnologica de Minas Gerais","correspondingAuthor":true,"prefix":"","firstName":"Henderson","middleName":"Soares","lastName":"Madureira","suffix":""},{"id":290639667,"identity":"68a2f0bf-4be2-4e28-b94e-6fa160fde3c9","order_by":1,"name":"Carlos Alberto Carvalho Castro Castro","email":"","orcid":"https://orcid.org/0000-0002-6433-9877","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Carlos","middleName":"Alberto Carvalho Castro","lastName":"Castro","suffix":""},{"id":290639668,"identity":"7a3cb7ee-083c-417d-a4c2-ef84536a263f","order_by":2,"name":"Claudio Turani Vaz","email":"","orcid":"https://orcid.org/0000-0002-2693-9791","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Claudio","middleName":"Turani","lastName":"Vaz","suffix":""},{"id":290639669,"identity":"6ad27e7f-b8e2-40c8-92dd-ab584e30bb64","order_by":3,"name":"Elaine Carbalo Siqueira Corrêa","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Elaine","middleName":"Carbalo Siqueira","lastName":"Corrêa","suffix":""}],"badges":[],"createdAt":"2024-04-01 19:26:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4202425/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4202425/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54831162,"identity":"1a5983c5-ca3c-4be8-99f8-5427073e9f4c","added_by":"auto","created_at":"2024-04-17 11:12:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":58017,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative design of a 2² factorial with 5 replicas at the central point\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/38f677440698480013a4b25c.png"},{"id":54831615,"identity":"4b3508e8-369b-4349-8b96-848eef5bfb13","added_by":"auto","created_at":"2024-04-17 11:20:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":14465,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic drawing of the test specimen for tensile testing.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/8f3a43acbbcdfff73fea210a.png"},{"id":54831164,"identity":"f7d384ef-61ba-495a-9f14-bdefedef8a1b","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":23701,"visible":true,"origin":"","legend":"\u003cp\u003eInfluence of mixing time and rotation speed on the energy input\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/19c671557ce032e63dbba107.png"},{"id":54831165,"identity":"20fcfdd0-b390-498f-a373-cb05cd238484","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":70502,"visible":true,"origin":"","legend":"\u003cp\u003eSurface Energy Graph (\u003cem\u003econfidence level \u003c/em\u003e0.95)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/a13b82a272f37baeef0565b2.png"},{"id":54831166,"identity":"c656f951-f617-4885-bd24-c89a7f0f866f","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":93787,"visible":true,"origin":"","legend":"\u003cp\u003eEnergy probability graph (confidence level 0.95)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/297f7974492621c95be3d043.png"},{"id":54831616,"identity":"234f8f48-78d5-469f-b0dd-51e9714a2fec","added_by":"auto","created_at":"2024-04-17 11:20:02","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":50728,"visible":true,"origin":"","legend":"\u003cp\u003eWelding parameters influence on the welded area shear strength.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/8e06447bf81cbcbebbbb3aff.png"},{"id":54831167,"identity":"fe12a2ad-26fa-46fb-87a4-0e0f9c434fff","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":331265,"visible":true,"origin":"","legend":"\u003cp\u003eTensile test specimens surface fractured - mixing time 3s- a)1435rpm, b)2000rpm, c)2565rpm\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/faf72e5df31596643806c7a2.png"},{"id":54831174,"identity":"96541bc6-b4e7-45d1-9779-5915c22b3acc","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":378377,"visible":true,"origin":"","legend":"\u003cp\u003eTensile test specimens surface fractured – rotation speed 2000 rpm - a)1.6s, b)3s and c)4.4s\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/12dce355a333e0267746edf3.png"},{"id":54831179,"identity":"c96e9c8d-9772-4e4f-bf57-a833949851b7","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":247375,"visible":true,"origin":"","legend":"\u003cp\u003eWeld spot cross section\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/37f35345b6139e78618efc1d.png"},{"id":54831172,"identity":"a8601c56-da2c-4f80-bfff-fc45c19baa99","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":296782,"visible":true,"origin":"","legend":"\u003cp\u003eWeld discontinuity – 1435rpm -3s\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/70b452159f39fba222f7a403.png"},{"id":54831175,"identity":"922bc2d0-9f0d-421f-9eb0-0be716f250fc","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":287987,"visible":true,"origin":"","legend":"\u003cp\u003ePresence of cracks starting from the discontinuity – 2000 rpm- 4.4s\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/eb29d63161ecc66c4313d5ec.png"},{"id":54831171,"identity":"70ce6484-d7dd-47dd-b6c7-3c01af53af9f","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":393520,"visible":true,"origin":"","legend":"\u003cp\u003eBase metal microstruture (3500x)\u003c/p\u003e\n\u003cp\u003eAlpha ferrite, retained austenite, bainite, martensite (denoted as \u003cem\u003eα γ \u003c/em\u003er, \u003cem\u003eβ\u003c/em\u003e, M respectively), and other constituents\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/fc592c51fac9735aeb9d699f.png"},{"id":54831176,"identity":"d838139d-b6d8-46b2-a465-63051a74deeb","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":253352,"visible":true,"origin":"","legend":"\u003cp\u003eMixed Zone microstructure (3500X) - a)1435-3s, b)2000-3s e c)2565-3s\u003c/p\u003e\n\u003cp\u003eAlpha ferrite, Widmanstatten ferrite, retained austenite, bainite, martensite (denoted as \u003cem\u003eα wα γ \u003c/em\u003er, \u003cem\u003eβ \u003c/em\u003erespectively), and other constituents\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/5d53318b12867a980f37e874.png"},{"id":54831617,"identity":"3f285f2c-6d9a-4a47-a4d1-557c73839e85","added_by":"auto","created_at":"2024-04-17 11:20:02","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":278665,"visible":true,"origin":"","legend":"\u003cp\u003eMixed Zone Detail MEV 3500X - a)2000-1,6s, b)2000-3s e c)2000-4,4s\u003c/p\u003e\n\u003cp\u003eAlpha ferrite, Widmanstatten ferrite, retained austenite, bainite, martensite (denoted as \u003cem\u003eα wα γ \u003c/em\u003er, \u003cem\u003eβ \u003c/em\u003erespectively), and other constituents.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/1ace3a2e912cf1a0fad2e1d7.png"},{"id":54831180,"identity":"64744e56-ce01-4aec-8a25-0ede2e163478","added_by":"auto","created_at":"2024-04-17 11:12:03","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":256988,"visible":true,"origin":"","legend":"\u003cp\u003eThermomechanically Affected Zone - MEV 3500X - a)1435-3s, b)2000-3s, c)2565-3s\u003c/p\u003e\n\u003cp\u003eAlpha ferrite, Widmanstatten ferrite, retained austenite, bainite, martensite (denoted as \u003cem\u003eα wα γ \u003c/em\u003er, \u003cem\u003eβ \u003c/em\u003erespectively), and other constituents.\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/c99cbfb9e11047074c5f02ae.png"},{"id":54831618,"identity":"b8d88c71-e589-4b1c-bbf6-45a46dc2436e","added_by":"auto","created_at":"2024-04-17 11:20:02","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":257437,"visible":true,"origin":"","legend":"\u003cp\u003eAnalysis of Thermomechanically Affected Zone - 3500X: a)2000-1.6s, b)2000-3s, c)2000-4.4s.\u003c/p\u003e\n\u003cp\u003eAlpha ferrite, Widmanstatten ferrite, retained austenite, bainite, martensite (denoted as \u003cem\u003eα wα γ \u003c/em\u003er, \u003cem\u003eβ \u003c/em\u003erespectively), and other constituents.\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/7ac43e5700ba39251b51f07a.png"},{"id":54831169,"identity":"9cc6b7b1-c835-4165-a20a-73f89f2596fb","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":325023,"visible":true,"origin":"","legend":"\u003cp\u003eWeld hardness profile and SZ average hardness as function of mixing time (rotation speed 2000rpm).\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/7788b0a058c552ecac8d413e.png"},{"id":54831178,"identity":"f8968c34-768a-4341-969b-ef0e8cbd2e83","added_by":"auto","created_at":"2024-04-17 11:12:02","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":291805,"visible":true,"origin":"","legend":"\u003cp\u003eWeld hardness profile and SZ average hardness as function of rotation speed (mixing time 3s).\u003c/p\u003e","description":"","filename":"18.png","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/fe3c9104fa8f3d6f3bb57687.png"},{"id":57777281,"identity":"6d30d2f7-bdb8-4cfb-a149-7a3772287418","added_by":"auto","created_at":"2024-06-05 13:50:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4280824,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4202425/v1/bd249234-f11d-450e-aed4-670a059c5eb4.pdf"}],"financialInterests":"","formattedTitle":"Microstructural and Mechanical Behavior of Welds in Partially Transformed TRIP 800 Steel Produced by Friction Stir Spot Welding (FSSW)","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eThe escalating concern regarding climate change has been a catalyst for the industry\u0026rsquo;s endeavors to adopt cleaner technologies and materials. Within this framework, a significant challenge confronting the automotive sector is the enhancement of energy efficiency while simultaneously meeting progressively restrict requirements for fuel consumption and safety standards. To address this demand, there is an increasing reliance on materials distinguished by lower thickness yet greater strength and toughness.\u003c/p\u003e \u003cp\u003eHistorically, until the 1980s, the mainly steels used in vehicle manufacturing featured a yield strength of 325 MPa. However, numerous applications have since shifted towards the use of Advanced High-Strength Steels (AHSS), which are characterized by yield strengths over than 780 MPa and, in some instances, reaching 1000 MPa.\u003c/p\u003e \u003cp\u003eThis transition has resulted in the production of considerably safer vehicles, with a final weight up to 35% lower. Notably, among these advanced steels are Transformation Induced Plasticity (TRIP) steels [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The TRIP effect involves a phase change from metastable austenite to martensite when deformation is applied, promoting grain reorientation and self-accommodation, also known as the Greenwood-Johnson effect and the Magee effect [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Typically, these low-alloy steels have a ferritic matrix structure composed of a fraction of 10 to 15% retained austenite with small inclusions at the grain boundaries. The use of TRIP steels is associated with excellent formability and high mechanical strength obtained after stamping operations combined with toughness. However, conventional welding methods like Resistance Spot Welding (RSW) may result in the formation of a fusion zone and a heated affected zone with a high volumetric fraction of martensite, which is brittle. To mitigate such effects, post-welding heat treatments are considered; however, this leads to a significant increase in manufacturing costs.\u003c/p\u003e \u003cp\u003eFriction Stir Welding (FSW) is a solid-state welding technique that initially emerged to weld non-ferrous materials but soon expanded to other alloys such as aluminum, magnesium, and copper [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Thermal input in FSW is generated by converting kinetic energy into thermal energy through friction between the shoulder, pin, and workpiece surface. The pin, which can have complex geometries, needs to be a few millimeters shorter than the sum of the thickness of the overlapped sheets or the thickness of the sheets in the case of butt welds [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Friction Stir Spot Welding (FSSW) is a variation of the FSW process, differing primarily in its localized application, targeting specific spot areas for welding. It offers an interesting alternative as it can minimize the effects of the welding thermal cycle and demonstrate good efficiency with lower energy consumption, combined with the absence of consumables such as shielding gases, fluxes, or filler material. The process requires high torque and forces necessary to mix the plasticized material and the tool, which must withstand these forces [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The most important parameters in the production of this type of weld are the mixing time, followed by rotation speed and penetration depth. The FSSW process, which starts with the predetermined rotation, initiates by applying normal force to the joint to be produced. The heated material is plasticized and stir, and the process continues for a predetermined time, followed by tool retraction [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTherefore, the study scope was to produce welds in TRIP 800 partially transformed, condition frequently met in automotive industry, by FSSW process as a way to understand and overcome the challenges mentioned above. The effect of rotation speed and mixing time in the weld mechanical behaviour and microstructure were investigated. The microstructural changes were related to mechanical properties, i.e., weld shear strength and heat input during processing.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cp\u003eIn this study, TRIP 800 steel with a thickness of 1.5 mm and a typical chemical composition of C 0.19%; Si 1.65%; Mn 1.64%; Al 0.39%; P 0.16% was utilized. To determine the number of samples, a Central Composite Rotatable Design (CCRD) was employed, incorporating two factors: rotation speed (rpm) denoted as (B), and mixing time (A), each at two levels (2x2), in addition to four axial points (2x2), and the central point. The central point was reiterated five times, resulting in a total of 13 tests, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe preparation of the test specimens involved two stages. Initially, they were cut in the rolling direction and then subjected to a pre-deformation of 10% to promote the microstructural transformation induced by plasticity. For this purpose, an Instron model 5982 universal testing machine was used, along with the Blue Hill3 control and data acquisition system, employing a needle-type extensometer (Instron model 2630\u0026thinsp;\u0026minus;\u0026thinsp;106). This alloy is typically welded stamping, i.e., after the plasticity induced transformation phenomenon.\u003c/p\u003e \u003cp\u003eThe weld test specimens were produced according to the [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], with dimensions of 30 mm in width and 102 mm in length, cutted in the rolling direction. The sheets overlapping was 50 mm, and the formed weld spot was positioned centrally, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe factors interacting in the weld produced by the FSSW process are the rotation speed and mixing time, determined in preliminary tests. The tool pin penetration speed was set between 0.4 mm/s, as proposed in the literature. The samples were fixed in a device manufactured for this purpose, ensuring a perfect alignment and necessary overlap for weld production, according to the [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. A machining center, Romi model D800, was used for the FSSW process.\u003c/p\u003e \u003cp\u003eMicrostructural analysis to evaluate the present constituents/phases was performed using cutting, grinding, and metallographic polishing techniques to avoid the transformation of the present phases, which could lead to misinterpretations. The grinding techniques followed a stepped pattern of grit size (120, 220, 320, 400, 600, and 1200 mesh) with alternating grinding directions [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Subsequently, polishing was done using diamond paste (9, 3, and 1 micron) and chemical etching with a 3% Nital solution. Macrostructural analysis was conducted using a Zeiss STEMI 2000-C stereoscopic microscope equipped with a camera for image acquisition. To identify ferrite, bainite, martensite, and retained austenite, complementary microstructural analyses were performed using a Shimadzu SSX-550 Superscan scanning electron microscope, owing to grain refinement.\u003c/p\u003e \u003cp\u003eThe tensile test was carried out utilizing an Instron model 5982 universal testing machine with the Blue Hill3 control and data acquisition system. According to the [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], the deformation rate was set at 17 mm/min. Following the tensile test, the areas were determined by examining the images of the samples using the ImageJ software. The microhardness profile was obtained on the upper sheet, 0.25 mm from the lower side, across the entire section, including the stir zone, thermomechanically affected zone, thermally affected zone, and base metal. Indentations were made using a load of 0.200 Kgf for 10 seconds, with a 0.2 mm step between indentations, ensuring multiple hardness measurements of the matrix in each weld region with a Shimadzu HMV-20 hardness tester. Measurements of the weld regions were analyzed using the Image J. image analysis software.\u003c/p\u003e \u003cp\u003eThe energy input was indirectly calculated using data from voltage and current values collected with a U1242b multimeter and a U1212 Agilent ammeter at a rate of 10 data points per second at the output of the frequency inverter of the equipment. Data collection began with the start of pin penetration and ended with tool retraction. The energy values inputted into the process considered the rotation speed and mixing time.\u003c/p\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cp\u003eAs a solid-state joining process, the primary sources of heat in Friction Stir Spot Welding (FSSW) are the friction between the shoulder and pin of the tool and the material, which are correlated with the tool rotation speed and the plastic deformation the material undergoes. The calculated energy values for the welds produced with various parameter interactions are presented in Table I.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eTABLE I. Total Energy for Different Parameters\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRotation Speed (rpm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMixing time (s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEnergy (kJ)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1435\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e24.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e22.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2565\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e34.9\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\u003eThe supplied energy was calculated indirectly using Eq.\u0026nbsp;1, as cited in Eagar (1986) and employed by Khan [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], as a function of the normal force F, tool positioning X, torque τ, angular velocity ω, and process duration time. The data were collected at the output of the frequency inverter of the machine used. Since the tool does not move, the first part of the equation is disregarded, leaving only the relationship between angular velocity, torque, and time.\u003c/p\u003e \u003cp\u003e\u003cimg 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\"\u003e\u003cbr\u003e\u003c/p\u003e\u003cp\u003eThe data indicates that energy values increased with the increase in rotation and time; however, rotation has a greater influence on the energy input compared to the mixing time. The standardized effects graph of the parameters can be viewed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, generated using Minitab software. The rotation speed was found to be the most significant parameter.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe energy calculations exhibited a normal distribution with an 95% confidence level according to statistical analysis. However, it\u0026rsquo;s important to note that process losses were not factored in, and the collected energy data from the inverter output might not precisely reflect the actual values. Nonetheless, this consistent method was applied to all samples, ensuring consistency. A response surface showing the probability of generated energy is displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, created using Minitab software.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe probability of energy predictability is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, created using Minitab software.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe values of the welded area and the corresponding shear strength of the welds obtained for various parameter combinations are presented in Table II. The correlation analysis between the energy data and area did not reveal a direct relationship between these variables. Khan, in the experiments with transformable steels, described a similar effect, highlighting the lack of linearity between energy, yield strength, and welded areas, although was observed a larger welded area with the application of higher energy [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\"\u003e\u003cbr\u003e\u003c/p\u003e\u003cp\u003eIn this specific study, the welded area varied around a mean value, making it difficult to identify a clear trend. However, Feng observations suggest that increasing the time in experiments resulted in an expanded bonding region [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Indeed, the nonlinearity observed in this study aligns with the complexity of the welding process and underscores the importance of considering additional factors. One such factor that may influence the formation of the weld region thickness, but has not been evaluated before, is the pressure exerted by the tool. Xie, citing Santella et al., argues that, for the same material, higher pressure can have a significant impact on the strength limit [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The relationship between weld area and shear strength for various rotation speeds and mixing times is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The lack of a clear correlation between these variables suggests the potential influence of other factors on the shear strength limit.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRemarkably, the weld achieved at a rotation speed of 2000 rpm and 4.4 seconds exhibited unusually the lowest shear strength limit. In this case, the area of the welded region increased compared to the weld obtained at 2000 rpm and 3 seconds. This discrepancy could arise from the formation of different constituents or discontinuities during the process, potentially diminishing both the strength and the effectively welded area. Such conditions might have contributed to the weld\u0026rsquo;s early failure.\u003c/p\u003e \u003cp\u003eWhen comparing the images, it becomes evident that there is a lack of a consistent fracture pattern, except for the fact that it seems to have originated at a point along the line formed between the sheets. It is noteworthy in this case that such occurrence indicates a partial union or even absence thereof at the outer end of the joint. This failure process traverses the line formed on the lower sheet until reaching the rupture in the stir zone of the upper sheet. The macrographs, which provide a visualization of the fractured surface aspect of the welds after the test, are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe macrographs of the welded specimens revealed distinctive regions whose size and composition varied depending on the parameters employed affected by process energy. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e presents a typical weld cross-section, delineating the stir zone, thermomechanically affected zone, thermally affected zone, and base metal, as elucidated by [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] and further classified into sub-regions by [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. The microstructural examination specifically targeted the central points within these regions to assess the constituent elements.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAdditionally, the formation of a discontinuity situated between the welded plates and the coalesced material, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, was observed in all welds. This phenomenon tends to become more visible when the distance, created by the central pin promoting material mixing, increases. The dimensions of it tend to reduce with material diffusion become more effective by heating, which intensifies with the proximity of the central pin. Rotation speed also influences this, as noted by [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eObserving the highlighted detail in the figure, can be noted the presence of acute angles on the outer part, formed between the coalesced material that was forced between the plates during the tool pin movement. Under certain processing conditions, as illustrated in the macrograph in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, the presence of cracks was observed starting from the edge of the discontinuity. Internal stresses resulting from welding or external forces can propagate it, potentially leading to the total failure of the weld. This phenomenon is commonly observed in welds with high energy in transformable steels, in which cracks propagate through the mixing zone until complete failure [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe discontinuity formation, indicating a mixing lacking mainly in the external regions where the maximum temperatures are lower, was observed in all welds produced. However, it is more evident in the weld depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, which was produced using 2000 rpm (rotation speed) and 4.4 seconds (mixing time) where a crack appears at the end of the discontinuity located along the mixed and thermomechanically affected zones in the bottom position.\u003c/p\u003e \u003cp\u003eThe base metal microstructure is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e showcasing ferrite, martensite, bainite, and retained austenite even after the initial plastic deformation of 10%. The presence of martensite is not inherent to this steel in as-received condition indicating an effective transformation phenomenon induced by plasticity. The martensite fraction observed results from the TRIP effect, leading to a decrease in the fraction of retained austenite. The remaining fraction suggests that the transformation effect can still manifest in this material under stress and deformation.\u003c/p\u003e \u003cp\u003eThe images captured with SEM at a magnification of 3500 times depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e represent the mixed zone of the welds generated by using a mixing time of 3 seconds across three distinct rotation speed levels. Generally, a microstructure predominantly comprising martensite and bainite is discernible.\u003c/p\u003e \u003cp\u003eThe presence of martensite can be attributed to cooling rates surpassing the critical value during welding cycle, in a region where maximum temperatures reached is higher than those necessary for complete austenitization. Additionally, it is evident that the rise in rotation speed led to an enlargement in the size of the martensite laths. This observation can be linked to the development of larger austenitic grains in processes conducted at higher rotation speeds, which are correlated with increased input energy and, consequently, higher peak temperatures. This effect is consistent with Mazzaferro findings that higher rotation speeds resulted in a decrease in both the quantity and size of bainite grains in similar materials [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. As the rotation speed increases, martensite plates tend to enlarge while bainite experiences a reduction in quantity and size.\u003c/p\u003e \u003cp\u003eIn another hand, images from Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e obtained using SEM, reveal the impact of mixing time on the constituents at a fixed rotation speed parameter of 2000 rpm. The mixed zone exhibits a refined structure predominantly composed of martensite along with what appears to be bainite. This is consistent with findings in other samples where the presence of martensite is likely attributed to the critical cooling temperature reached after attaining the austenitization temperature. Any austenite that did not undergo martensitic transformation may persist as retained austenite or decompose into bainite.\u003c/p\u003e \u003cp\u003eIn the sample with a time of 1.6 seconds, the presence of ferrite was restricted and localized at certain grain boundaries, a phenomenon not observed in other samples. Additionally, the size of martensite plates tends to increase with higher energy input in the process, which, in this case, is directly correlated with time.\u003c/p\u003e\u003cp\u003eAustenite that has not undergone martensitic transformation may persist in the form of retained austenite or decompose into bainite. The observed martensite plates also tend to be larger with higher energy in the process, which, in this case, is associated with the growth of austenitic grain favored by mixing time increasing.\u003c/p\u003e \u003cp\u003eThe mixed zone exhibits a refined structure primarily composed of martensite and bainite, which is consistent with earlier observations. The presence of martensite is likely linked to the critical cooling temperature after reaching the austenitization temperature. Austenite that hasn\u0026rsquo;t undergone martensitic transformation may persist as retained austenite or decompose into bainite. Larger martensite plates are observed with higher energy in the process, likely due to increased growth of austenitic grain facilitated by time and rotation speed.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e shows the thermomechanically affect zone constituents of the welds produced at rotation speeds of 1435 rpm, 2000 rpm, and 2565 rpm, with a welding time of 3 seconds. The sample with a rotation speed of 1435 rpm exhibits a structure closer to that of the base metal. It is possible that this region did not reach temperatures to promote significant changes in constituents, and the martensite likely resulted from the initial 10% deformation. In the sample produced using 2000 rpm, there was a decrease in the amount of austenite, accompanied by the growth of ferrite grains and an increase in bainite, which is expected from austenite decomposition. The occurrence of retained austenite is also minimal, and existing martensite likely must be related to the initial deformation. The sample with a parameter of 2565 rpm exhibited a martensitic matrix. Alongside martensite, there is an expected bainite constituent, with ferrite occurring in small amounts and the presence of retained austenite is minimal.\u003c/p\u003e \u003cp\u003eIn these instances, the formation of higher hardness constituents in the thermomechanically affected zone correlated with increased rotation speed. This could be attributed to the higher peak temperatures reached, as noted by Mazzaferro (2008), potentially leading to the attainment of the austenitization temperature.\u003c/p\u003e \u003cp\u003eWeld microstructure produced with fixed rotation speed (2000 rpm) but varying in mixing time is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e. The weld made with a time of 1.6 seconds demonstrates a reduction in retained austenite within the thermomechanically affected zone compared to the base metal. The presence of martensite is likely due to the initial 10% deformation, with small occurrences of austenite and bainite. In contrast, the weld with 3 seconds mixing time showcases an increase in ferrite grain size and a higher amount of bainite resulting from austenite decomposition when compared to the weld with a 1.6 second.\u003c/p\u003e \u003cp\u003eThe weld with a mixing time of 4.4 seconds exhibited a martensitic matrix accompanied by what seems to be bainite in smaller proportions. Among all samples, this one displayed the highest martensite content in the thermomechanically affected zone, suggesting extensive austenitization with a longer mixing time. This, coupled with critical cooling rates, facilitated the formation of significant quantities of martensite. The development of internal stresses may have contributed to the crack observed earlier in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. In these instances, the formation of higher hardness constituents in the thermomechanically affected zone was observed with an increase in mixing time.\u003c/p\u003e \u003cp\u003eVarious parameters influenced the behavior of the weld, leading to alterations in the dimensions of the formed zones and the resulting microstructures. Hardness profiles were obtained through tests performed using a Vickers Hardness tester, and indentations were made to analyze the hardness of the constituents formed in different regions. Although the hardness values in the mixed zone are similar, the size of martensite plates increased with the rotation speed. Additionally, the thermomechanically affected zone exhibited a composition with a higher fraction of microconstituents, such as martensite and bainite, at higher rotation speed values. Lower values allowed the presence of constituents like ferrite and retained austenite, remaining from the base metal.\u003c/p\u003e \u003cp\u003eThe hardness profile conducted on samples with a base time of 3 seconds and rotation speeds of 1435, 2000, and 2565 rpm is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003e, revealing consistent values with the founded mixed zone microstructure. As the rotation speed increased from 1435 to 2565 rpm, hardness values exhibited a slight reduction, a phenomenon also noted by Mazzaferro (2010) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This reduction could be attributed to the larger size of martensite plates. However, the values, when considered alongside the standard deviation, overlap, hindering a definitive conclusion about the trend. Furthermore, hardness values decrease as one moves away from the mixed zone, a pattern observed by both Feng (2005) and Mazzaferro (2010) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. It is hypothesized that the transformation of martensite in the mixed zone is linked to the critical cooling rate after reaching temperatures AC1 and AC3 with a high degree of austenitization.\u003c/p\u003e \u003cp\u003eThe hardness profile depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e18\u003c/span\u003e for samples with a fixed rotation speed of 2000 rpm and varied times (1.6 s, 3 s, and 4.4 s) showed typical hardness expected considering the founded mixed zone microstructure. Comparing the average hardness of mixed zone is observed a slight reduction with a mixed time increasing but the variations are within standard deviation. This behavior must be related to the thermal cycle and the resulted microstructure which presents differences in the martensite laths.\u003c/p\u003e \u003cp\u003eIn all samples, the thermomechanically affected zone serves as a transition area where hardness values decrease as one moves away from the mixed zone to base metal, as observed in the hardness profile. This can be clearly understood by the microstructure formed in this region. The microstructural variations resulted by rotation speed and mixed time changes also must be observed in the hardness profile. In turn, as expected, the thermally affected zone tends to presents hardness close to the base metal.\u003c/p\u003e"},{"header":"4. CONCLUSION","content":"\u003cp\u003eIn this paper, the effects of the rotation speed and mixing time in friction spot welding of a TRIP 800 steel, after undergoing a plastic deformation of 10%, were investigated. Based on these results and the analyses of the conducted tests, the following conclusions can be drawn:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eRegarding the energy input in the process, it was observed that the rotation speed is more relevant than the time;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIt was not possible to establish a linear relationship between the area of the welded region and the energy, nor with other parameters involved in the process. Additionally, the effect of pressure on the welding process was not investigated, which could be considered a topic for future studies;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe analysis of the effects of time and rotational speed parameters on the mixed zone reveals that, as the rotation speed increases, there is an increase in martensite plates accompanied by a reduction in the bainite constituent. The significant presence of martensite can be attributed to heating up to the austenitization temperature, correlated with the growth of austenitic grains. These austenitic grains have the potential to transform into martensite when the critical cooling rate is reached, while grains that do not undergo this transformation may remain as retained austenite or decompose into bainite.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe analysis of the effects of mixing time and rotation speed parameters on the thermomechanically affected zone showed these factors increase, there is a reduction in ferrite and austenite, accompanied by an increase in the bainite and martesite constituents. The presence of martensite in this case must be related to the pre-deformation of the material and peak temperatures above austenitic transformation.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eRegarding the microhardness profiles, it can be observed that the graphs presented three distinct regions, with the mixed zone reaching high hardness values consistent with the martensitic microstructure found. The thermomechanically affected zone appears as a transition zone with a decrease in hardness as the distance from the mixing pin increases up to the thermally affected zone, which has hardness similar to that of the base metal;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe formation of discontinuities occurred, indicating localized failure in the material joining and likely where the rupture process must initiate. Under specific conditions cracks originated and propagated through the mixed zone.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe authors\u0026rsquo; of this manuscript declare that there is no conflict of interests regarding submission and publication of this manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors would like to acknowledge Centro Federal de Educa\u0026ccedil;\u0026atilde;o Tecnol\u0026oacute;gica de Minas Gerais (CEFET- MG). This work was partially supported by Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior Brazil (CAPES) - Financing Code 001.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWANG W, ZHANG S, QIAO K, WANG K, PENG P, YANG Q (2019) Microstructure and mechanical properties of friction stir welded joint of TRIP steel, 2020. Editorial board J Mater Sci Technol. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.1016/j.jmapro.2020.05.045\u003c/span\u003e\u003cspan address=\"10.1016/j.jmapro.2020.05.045\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eREISNER FISHERFD, WERNER G, TANAKA EA, CAILLETAU K, ANTERETTER G (2000) A new view on transformation induced plasticity (TRIP). 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In: \u003cem\u003eSAE International View list of content related to the publisher(s) In United States\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.4271/2005-01-1248\u003c/span\u003e\u003cspan address=\"10.4271/2005-01-1248\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMAZAFERRO MAZZAFERROCCP;RAMOSDF, ROSENDO JAE, Dos TS, ROSENDO SANTOSJF (2009) T. S.; STRO- HAECKER T. R.; TIER M. A. D; DA SILVA. A. Microstructure evaluation and mechanical properties of a friction stir spot welded TRIP 800 steel, 2009. In: \u003cem\u003eDepartamento de Engenharia de Materiais, Centro Federal de Educac\u0026cedil;a˜o Tecnologica de Minas Gerais - Brasil\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003edoi.org/10.1590/S0104-92242009000400002\u003c/span\u003e\u003cspan address=\"10.1590/S0104-92242009000400002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eROSENDO MAZAFERROCCP, TIER TS, M. A. D.; MAZAFERRO JAE, Silva D (2010) A. M. STROHAECKER T. R. Friction stir spot welding of a trip steel: microstructural characterization/Soldagem a ponto por fric\u0026ccedil;ao e mistura mec\u0026acirc;nica de um a\u0026ccedil;o trip: caracteriza\u0026ccedil;\u0026atilde;o microestrutural. In: Tecnologia em Metalurgia e Materiais\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Friction welding, TRIP steel, Microstructure, Mechanical properties","lastPublishedDoi":"10.21203/rs.3.rs-4202425/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4202425/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe industry\u0026rsquo;s pursuit of clean technologies and materials amidst growing concerns about climate change underscores the significance of innovative welding processes. The utilization of TRIP 800 steel, renowned for its transformation-induced plasticity, highlights the endeavor towards enhancing energy efficiency and safety in the automotive sector. Nevertheless, welding this material poses significant challenges, particularly in the formation of martensitic regions in the weld zone, potentially resulting in reduced ductility and increased brittleness. Additionally, the thermal cycle involved in the welding process may induce unfavorable microstructural changes, affecting the overall integrity of the welded joint. Despite these challenges, FSSW emerges as a promising alternative to traditional welding processes, offering advantages such as reduced energy consumption and enhanced mechanical properties. This study aimed to investigate welds in TRIP 800 steel sheets through the Friction Stir Spot Welding (FSSW) process after deformation, thereby reflecting broader applications beyond vehicle manufacturing. The interaction of factors, including time and rotation speed, was examined at various levels for microstructural characterization, tensile and microhardness tests, showcasing the versatility and potential of the FSSW process. The analysis of welded joints revealed distinct regions such as the stir zone, thermomechanically affected zone, thermally affected zone, and base metal, illustrating the complexity and precision of modern welding techniques. Notably, the study delved into the microstructures of the affected zones, elucidating their pivotal role in influencing mechanical behavior under load conditions until failure. This investigation contributes to the ongoing quest for innovative solutions in vehicle manufacturing, emphasizing the importance of understanding welding processes and material properties in achieving sustainability and performance goals.\u003c/p\u003e","manuscriptTitle":"Microstructural and Mechanical Behavior of Welds in Partially Transformed TRIP 800 Steel Produced by Friction Stir Spot Welding (FSSW)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-17 11:11:57","doi":"10.21203/rs.3.rs-4202425/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d323dc75-6ea5-47e2-a4a2-44babe0198a5","owner":[],"postedDate":"April 17th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-05T13:42:02+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-17 11:11:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4202425","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4202425","identity":"rs-4202425","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}