Experimental Investigation of Hot Forming of Zn‐Coated Hot‐Stamping Steel

An investigation on the thermal property, fracture mechanism of substrate and coating layer, liquid‐metal embrittlement (LME) crack, coating layer morphology, microstructure, and hardness of Zn‐coated hot‐stamping steel is presented. The effect of forming temperature on the LME is studied. The crack mechanism of substrate at elevated temperature is ductile fracture with various‐sized dimples. The inclusions in the dimples are also detected and researched. However, the fracture mechanism of coating layer and weld spot is different from that of substrate. At high temperature, the liquid Zn invades into the substrate with oxidation reaction, which reduces the thermal formability. The complex chemical reaction and different phase formation occur in the coating layer. The coating layer breaks and peels off from the substrate with sharp edge, indicating brittle fracture. The phase of substrate mainly transforms into martensite phase with the microhardness Vickers hardness 0.2 of 410–490.