Study on Cracking Behavior of High-Strength Steels by Liquid Zinc-Induced Embrittlement

Although Zn-coatings have enhanced corrosion resistance of steels, Zn-induced liquid metal embrittlement (LME) is susceptible during hot forming. Prolonging the annealing time before hot forming availably prevents LME by eliminating the liquid phase. Herein, the austenitization process window by systematically investigating the effects of annealing time on the mechanical properties of high-strength (press-hardened 22MnB5, dual-phase DP980, and quenching-partitioning QP1180) steels and LME cracking behaviors for corresponding galvanized (GI) steels are optimized. The results support LME undermines the mechanical properties of all GI steels, while the effecting of the coating for the 22MnB5 is few. Calculation of phase diagram (CALPHAD) is used to evaluate the influence of annealing time on the ductility of the steels. Furthermore, the formation mechanism of LME cracks during the austenitization of galvanized QP1180 is studied. At the initial stage, the interfacial Fe-Al inhibition layer is destabilized. The cracks initiated on the surface of gamma-Fe are induced by the synergistic effect of strain and penetration of liquid Zn. The results of transmission electron microscopy (TEM) indicate that Fe-Zn compound (Gamma-Fe3Zn10) is created and carbon enriches at the interfaces between the infiltrating Zn and gamma-Fe substrates at the LME crack tips.