A shrinkage-based criterion for evaluating resistance spot weldability of alloyed steels

For many decades, several classical formulas on carbon equivalent (CE) have been widely used for evaluating the weldability of steels. Unfortunately, a single CE is impossible for various types of steels. In this study, the resistance spot weldability of medium-Mn steels was investigated. In particular, the influences of paint baking processes at different temperatures on the mechanical properties, fracture mode, and microstructure of weldment were studied. It was found that the paint baking above 170°C can change the tensile-shear failure of weldment from the undesired interfacial failure to the desired pull-out one, because the shrinkage of weldment during welding was compensated by the thermal expansion during the baking, leading to the "cold welding" realized for solid joining. Furthermore, a shrinkage-based criterion (∆l) was established for evaluating the weldability of greater range of alloyed steels more accurately and robustly than CE. The proposed criterion on measuring the weldability of high alloyed steels opens a promising path forward for designing a new generation of advanced high strength steels requiring good weldability.