점용접 시 발생하는 용융 아연 취화에서 Fe-Zn 합금화 반응의 중요성

Abstract

In the resistance spot welding (RSW) process, galvanized steel sheets are exposed to high temperature and stress, which may cause Zn-assisted liquid metal embrittlement (LME) cracks. TWIP steels with fully austenitic microstructure and similar grain size were prepared to investigate Si and Al alloying effects on Zn-assisted LME. The base steel composition was 17Mn-0.4C, and the Si and Al contents were controlled to be 0 wt%, 0.5 wt%, and 1.5 wt%, respectively. Resistance spot welding was conducted to evaluate the severity of LME. In addition, heat treatment was carried out to investigate the Fe-Zn reaction at the Zn coating/steel interface. With the increase of Si content in the steel, the maximum length of Zn penetration increased, and the generation frequency also increased, which was not seen in the Al-containing TWIP steels. This tendency strongly correlated with the Fe-Zn reaction rate and the morphology of -Fe(Zn) at the Zn coating/steel interface. The role of Si on the formation of Fe-Zn phases and its effect on LME were analysed, and the mechanism for Zn penetration into the steel sheet during the resistance spot welding was suggested.