Mechanical Properties and Failure Mechanism of Resistance Spot Welding Joint of 0.13C – 6.98Mn Medium Manganese TRIP Steel

A single-pulse spot welding test was performed on 0.13C-6.98Mn medium manganese TRIP steel. The test results showed that the joint performance increases with a rise in welding heat input before splashing occurs. Owing to the fusion zone (FZ) being closest to the heat source, its austenite content was completely transformed and its performance was worse than that of the heat affected zone comprising austenite. The segregation bands of C and Mn observed in the FZ were considered to be the main reason for the deterioration of grain boundary strength. These characteristics of the weld zone led to evident intergranular cracking and transgranular fracture in the tensile test, and all samples in this test showed partial or complete interfacial fractures.

Keywords:
resistance spot welding; medium manganese TRIP steel; microstructure; fracture mechanism