Effect of Microstructure and Chemical Composition on the Liquid Metal Embrittlement of Advanced High Strength Steels

Abstract

This study examines the susceptibility of Fe-0.2C-2Mn-0.41Cr advanced high-strength steels (AHSS) to Zn-induced Liquid Metal Embrittlement (LME) during resistance spot welding (RSW) and hot tensile testing, focusing on the effects of Si and Mo. RSW trials on electrogalvanized sheets showed that a 1.5Si alloy exhibited longer cracks than a 0.6Si alloy due to Si’s role in inhibitinh Fe-Zn reactions and prolonging grain boundaries’ exposure to liquid embrittler. Adding 0.2 wt% Mo to a 1.5Si steel improved LME resistance by increasing tensile stroke and reducing crack length. Mo promoted Zn diffusion into the substrate, forming Zn-ferrite, and enhanced grain boundary cohesion via B segregation. Ultimately, a physics-based semi-quantitative model was developed to assess LME susceptibility, showing that how LME severity depends on grain size, temperature, stress, and strain rate. The model highlights Si’s detrimental role and predicts Mo’s potential in mitigating LME, offering insights into optimizing AHSSs for automotive applications.