Optimization of Hot Forming Temperature to Minimize Liquid Metal Embrittlement Induced Cracking in Resistance Spot Welded Zinc-Coated Medium Manganese Steel

Abstract

Herein, an investigation on the influence of the hot press forming (HPF) temperature cycles of a medium manganese, high ductility, zinc-coated steel with ≈1000 MPa final tensile strength (HPF1000-GI), with a specific emphasis on the risks of liquid metal embrittlement (LME) induced cracking during resistance spot welding (RSW) is presented. The HPF1000-GI steel is hot press formed using several temperature cycles, and subsequently the LME sensitivity of the variously hot press formed materials are investigated using both dedicated RSW experiments as well as high-temperature tensile testing. It is shown that the LME sensitivity of the HPF1000-GI steel is significantly reduced after hot forming at higher intercritical temperatures, and that this favorable behavior is caused by microstructural changes at the coating-substrate interface.