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<p>Resistance spot welding (RSW) is widely utilized in the automotive and manufacturing industries for joining high-strength materials such as AISI 420 martensitic stainless steel (MSS). However, MSS spot welds exhibit low fracture toughness due to the formation of a brittle martensitic microstructure in the fusion zone (FZ), impairing weldability. This study investigates the influence of two distinct welding strategies: the weld nugget forming strategy (WNFS) and the weld nugget in-situ tempering strategy (WNTS) to enhance joint performance and mitigate these challenges. A Box-Behnken design of experiments was adopted to systematically vary weld current, weld time, and electrode force on weld quality. Weld quality was assessed using nugget diameter, peak load, and absorption energy. Tensile-shear strength, microhardness profile, and fatigue life were evaluated to characterize mechanical behavior. The microstructural analyses were conducted using optical microscopy (OM), field emission scanning electron microscopy (FESEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) to characterize the phases and morphological features of the welded regions. Analysis of Variance was conducted to evaluate the significance level of the welding parameters. Furthermore, the Teaching-Learning Based Optimization (TLBO) algorithm was employed to identify the optimal parameter set. Fatigue testing (<i>R</i> = 0, 10&#xa0;Hz) showed that within the tested range of post-weld tempering durations, the in-situ tempering strategy (WNTS) provided improved fatigue life, with a maximum of 8885 cycles achieved at a tempering time of 0.36&#xa0;s. However, extending the tempering duration to 0.44&#xa0;s reduced fatigue resistance due to over-tempering effects, indicating that further work is needed to generalize these findings across different loading frequencies and materials. This work proposes an optimized RSW strategy advancing the weldability of AISI 420 MSS for structuring demanding applications through data-driven optimization.</p>

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Optimization of mechanical properties and microstructure characterization of resistance spot welded martensitic stainless steel: in-situ tempering and TLBO approach

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月10日

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  • Vinayak Gurav,
  • Divya Shrivastava

摘要

Resistance spot welding (RSW) is widely utilized in the automotive and manufacturing industries for joining high-strength materials such as AISI 420 martensitic stainless steel (MSS). However, MSS spot welds exhibit low fracture toughness due to the formation of a brittle martensitic microstructure in the fusion zone (FZ), impairing weldability. This study investigates the influence of two distinct welding strategies: the weld nugget forming strategy (WNFS) and the weld nugget in-situ tempering strategy (WNTS) to enhance joint performance and mitigate these challenges. A Box-Behnken design of experiments was adopted to systematically vary weld current, weld time, and electrode force on weld quality. Weld quality was assessed using nugget diameter, peak load, and absorption energy. Tensile-shear strength, microhardness profile, and fatigue life were evaluated to characterize mechanical behavior. The microstructural analyses were conducted using optical microscopy (OM), field emission scanning electron microscopy (FESEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) to characterize the phases and morphological features of the welded regions. Analysis of Variance was conducted to evaluate the significance level of the welding parameters. Furthermore, the Teaching-Learning Based Optimization (TLBO) algorithm was employed to identify the optimal parameter set. Fatigue testing (R = 0, 10 Hz) showed that within the tested range of post-weld tempering durations, the in-situ tempering strategy (WNTS) provided improved fatigue life, with a maximum of 8885 cycles achieved at a tempering time of 0.36 s. However, extending the tempering duration to 0.44 s reduced fatigue resistance due to over-tempering effects, indicating that further work is needed to generalize these findings across different loading frequencies and materials. This work proposes an optimized RSW strategy advancing the weldability of AISI 420 MSS for structuring demanding applications through data-driven optimization.