Study on microstructure and mechanical properties of spot welded joints of TRIP980 high strength steel

TRIP980 high strength steel was welded by resistance spot welding. By optimizing the parameters and process of resistance spot welding, the variation of microstructure and mechanical properties of weld nugget was studied. The results showed that the microstructure of nugget was gross martensite structure, the hardness of the joint was 617.1 HV and the maximum tensile force was 17.8 kN when optimized welding parameters were 9.5 kA, 22 cycle, 3 kN. Temper process was performed on the basis of this. When the tempering current and time were 6.3 kA and 13 cycles, respectively, the grain size of the joint microstructure was the smallest, the joint hardness reduced to 574 .0 HV, and the joint tensile force was increased to 19.5 kN, increased by 9.6%. The fracture form was transformed from the original interface fracture to the button fracture.