Effect of Grain Size and Dislocation Density on the Work Hardening Behavior of SS 304

In the present investigation, grain size and dislocation density in SS 304 metastable austenitic stainless steel were varied by annealing the as-received steel at 1025 °C for 120 and 360 min. Effect of dislocation density and grain size on the work hardening behavior, evolution of deformation-induced martensite, and kinetics of deformation-induced transformation has been systematically studied with x-ray diffraction and microscopic examination of steels when subjected to the interrupted tensile deformation. As-rolled stainless steels exhibited rapid work hardening at low strains due to high initial dislocation density, while annealed steel rapidly work-hardened at higher strains due to the formation of large fraction of deformation-induced martensite and generation of large number of geometrically necessary dislocations. Differences in the initial dislocation density influenced the rate of deformation-induced transformation. Further, in this study, from first principles, it has been found that due to relatively high apparent stacking fault energy, in as-rolled fine grain stainless steels, deformation of austenite primarily takes place with the formation of twins. In contrast, annealed coarse-grained stainless steels with low apparent stacking fault energy, deformation-induced transformation of austenite into \(\epsilon \) $ϵ$ -martensite is the dominant deformation path, rendering annealed steel to undergo deformation-induced transformation rapidly as compared to the as-received stainless steel.