Stability of retained austenite in high carbon steel – Effect of post-tempering heat treatment

Highlights: • Effect of post-tempering heat treatment on hardness and stability of RA has been investigated • The dislocation density and deformation mechanism of phases are affected by the tempering • Tempering facilitates the diffusion of carbon from martensite to RA, promotes nano carbides formation and decreases the overall hardness -- Abstract: This work represents a fundamental study that investigates the effect of post-tempering heat treatment on hardness and the stability of retained austenite in dual phase high carbon steel. This influence was investigated focusing on micro to nano-scale stability of retained austenite and nanomechanical properties of the individual grains. Depending on heat treatment history of dual-phase high carbon steel, austenite grains will have different mechanical stability. In this study, samples with and without post-tempering heat treatment were produced while keeping other processing condition similar. Microstructural investigations, hardness test, and compression test were carried out on both samples to identify the characterization of different phases. The dislocation density and deformation mechanism of phases was affected by the tempering due to the redistribution of C content within the grains. Tempering facilitated the diffusion of carbon from martensite to retained austenite and the formation of nano carbides in the martensite matrix, therefore, decreased the hardness of martensite. The overall hardness of the material was decreased by ~16%. However, the stability of retained austenite at nano and bulk scale increased significantly as a result of tempering. These results revealed a valuable understanding for designing the low alloyed high carbon steel for industrial application.