Deformation at Room and Low Temperatures and Martensite Transformation in Resistance Spot Welding Duplex γ & α(δ) Materials of 301L Stainless Steel

Transformation induced plasticity （TRIP） and twinning induced plasticity （TWlP） effects had been widely studied in single austenite steel. But in duplex γ ＆ α（δ） phase, such as welding materials of stainless steel, they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy （SEM） as well as X-ray diffraction （XRD） were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4% α（δ） ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.