Liquid-Metal-Induced Embrittlement of Zn-Coated Hot Stamping Steel

Liquid-metal-induced embrittlement (LMIE) of galvanized hot stamping steel occurs due to the simultaneous application of stress and the presence of a liquid Zn surface layer during the hot stamping process. The mechanism specific to the liquid metal induced embrittlement occurring during hot stamping was investigated in detail. It was found that when a tensile stress was applied, liquid Zn could penetrate along grain boundaries in the steel matrix at temperatures above the Liquid + alpha-Fe (Zn) -> I(1) peritectic transformation temperature of 1055 K (782 A degrees C). The results show that an increase of the annealing time prior to hot stamping is an effective way to prevent LMIE by the elimination of the liquid phase.