Significant effect of magnetism on grain boundary segregation in γ-Fe: a systematic comparison of grain boundary segregation in nonmagnetic and paramagnetic γ-Fe by first-principles calculations

In the development of high-strength steels for carbon neutrality, it is important to control grain boundary (GB) segregation in paramagnetic γ-Fe. Recently, many studies have been performed in this direction using first-principles calculations; however, in most of them, γ-Fe was treated as nonmagnetic (NM). In the present study, the effect of magnetism on GB segregation in γ-Fe was investigated by systematically calculating and comparing the GB segregation of nine transition-metal alloying elements using NM γ-Fe and γ-Fe with the magnetic structure of the antiferromagnetic double-layer (AFMD)—a simple approximation of paramagnetism. It was found that AFMD γ-Fe, which has lattice constants and elastic properties similar to those of paramagnetic γ-Fe, can reproduce the GB segregation in paramagnetic γ-Fe well, whereas NM γ-Fe significantly overestimates the GB segregation tendency or leads to qualitatively incorrect conclusions. This study clarifies the importance of magnetism in γ-Fe using first-principles calculations and demonstrates an interesting relationship between metallurgical phenomena and magnetism.