Effect of Thermo-mechanical Treatment on the Formation Behavior of Martensite in 316L Stainless Steel

This study was carried out to investigate the effect of thermo-mechanical treatment on the formation behavior of martensite in 316L stainless steel. Dislocation, α and ε-martensite were formed by thermo-mechanical treatment. Martensite with surface relief and specific direction was formed by thermomechanical treatment. Martensite formed by thermo-mechanical treatment were reversed to austenite with an ultra-fine grain size of less than 1 μm by annealing treatment at 700 .deg. C for 20 min. α -martensite with a K-S orientation relationship and ε-martensite with a [110] [100]ε orientation relationship to the matrix was formed by thermo-mechanical treatment. The volume fraction of dislocation, α and ε-martensite were increased with the cycle number of thermo-mechanical treatment. In 5-cycle number thermo-mechanical treated specimens, more than 25% of the volume fraction of α -martensite and less than 5% of the volume fraction of ε-martensite were attained. The austenite grains were fairly deformed by thermo-mechanical treatment and the grain size of austenite with various orientation relationship were changed from micrometer to sub-micrometer by the 5-cycle thermo-mechanical treatment.