Effect of Cooling Rate of Heat Treatment on Microstructure Evolution of Hot Rolled 316L Stainless Steel

The effect of cooling rate of heat treatment on microstructure evolution of hot rolled 316L stainless steel was studied by high temperature laser confocal microscopy, nano-indentation and EBSD. The results show that the microstructure of 316L hot-rolled plate is banded structure, the austenite grains are elongated. The hardness of long second phase is 13.48 GPa, which is twice of austenite. Its internal phase structure is complex, which is composed of austenite, ferrite and Sigma (sigma) phase. In-situ observation shows that the ferrite and sigma phase in the second phase begin to transform to austenite when the temperature reaches 1065.4 degrees C. After holding at 1200 degrees C for 10 min, the austenite grains in the original second phase region are still rich in Cr and Mo elements. After cooling, the austenite therefore transforms to ferrite/sigma phase. The initial deformation texture weakens and transforms into random texture at different cooling rates. The homogenization degree and the content of austenite increase with the reducing of cooling rate. The austenite grains all transform from the second phase into ferrite at 500 degrees C/min, a small amount of sigma phase appears at 100 degrees C/min, and most of ferrite transforms into sigma phase at 12 degrees C/min.