Exploring the mechanism of solid-state transformation σ → γ during homogenization in 7Mo super austenitic stainless steel

Abstract

Topologically close-packed phases (TCP phase), with ordered dense-stacked structure, realize the atomic diffusion at high temperatures by forming the defects. In this study, we investigated the σ → γ transformation process at high temperature in cast 7Mo super austenitic stainless steel. Based on in-situ observation and microstructure analysis, it denoted that the modulated structure appeared in σ phase during the transformation process, which caused by the limited mobility of atoms. With extending homogenization time, the new γ phase formed at the boundaries of the modulated structure in σ phase. The size of the σ phase gradually decreased as new γ phase grew up. This discovery enriches the phase transformation mechanism of intermetallic compounds and provides a new sight for applying σ phase at high temperature.

Keywords

• Intermetallic compounds
• Phase transformations
• σ phase
• Austenitic steels