Phase Transformation During Intercritical Tempering with High Heating Rate in a Fe-13%Cr-4%Ni-Mo Stainless Steel

The phase transformation from martensite to austenite during intercritical tempering with high heating rate in a low carbon nnartensitic stainless steel Fe-13%Cr-4%Ni-Mo has been investigated to clarify the microstructure evolution in some regions of the weld joint heat affected zone (HAZ). The experimental results indicate that the start and finish temperatures of the martensite to austenite transformation keep constant when the heating rate is higher than. 10 K/s, and the transformation is much faster than nickel diffusion. The mechanism of the martensite to austenite transformation changes from diffusion to diffusionless during the intercritical tempering when the heating rate is higher than 10 K/s. The diffusionless transformation and higher A(s) temperature render it difficult for any austenite to remain at room temperature during the intercritical tempering with high heating rate that occurs in the HAZ. Adding a proper intercritical tempering with low heating rate can induce some reversed austenite in the rapid heated sample.