Effect of heat treatment at different cooling rates on phase transformation of hot rolled 316L

Abstract:

The microstructure, texture and phase transformation of hot rolled 316L stainless steel at different cooling rates were studied by high temperature laser confocal microscopy, nano-indentation and EBSD. The results showed that the second phase in hot rolled 316L plate had long strip shape with the hardness of 13.48 GPa. Its internal phase structure was complex, which was composed of austenite, ferrite and σ (sigma) phase. In-situ observation showed that the temperature reached 1065.4 ℃ at 457.01s, the ferrite and sigma phase in the second phase transformed to austenite. After 10 minutes of short homogenization, however, the austenite grains transformed from the second phase were still rich in Cr and Mo elements. After cooling, the austenite therefore transformed to ferrite / sigma phase and had similar long strip shape. The initial deformation texture weakened and transformed into random texture at different cooling rates. The homogenization degree and the percentage of austenite increased with the reducing of cooling rate. The austenite grains transformed from the second phase all transformed into ferrite at 500 ℃ / min, a small amount of sigma phase appeared at 100 ℃ / min, and mostly transform into sigma phase at 12 ℃ / min.

Key words:316L; cooling rate; microstructure; texture; phase