Zn-induced liquid metal embrittlement of galvanized high-Mn steel: Strain-rate dependency

Abstract

Zn-coated steel sheets suffer from Zn-induced liquid metal embrittlement (LME) during resistance spot welding and hot tensile deformation. By tensile testing at 700 and 800 degrees C, it was found that LME of an electro-galvanized high-Mn steel sheet was suppressed at low strain rate. Such strain-rate dependency of LME has been observed in various embrittlement metallic couples. Conventional ductile-to-brittle transition theory successfully explains the strain-rate reliance of LME in other embrittlement couples while it is invalid for Fe-Zn system. Owing to the high mutual solubility and several intermetallic compounds in Zn-rich regime of Fe-Zn system, the strain-rate dependency of Zn-induced LME was highly correlated with the existence of liquid Zn, which was verified by analyzing the cross section of the steel sheets.