Strain-Induced Martensite Formation and Recrystallization Behavior in 304 Stainless Steel

The effect of recrystallization on the evolution of microstructure, texture, and mechanical properties has been examined in an AISI 304 stainless steel, subjected to strain-induced α′-martensite transformation and subsequent annealing. Samples were processed by cold rolling and subzero rolling to induce different amounts of α′-martensite, using three reductions of 20, 40, and 60%, and later solution annealed to ensure complete recrystallization. Large transformation to α′-martensite occurred for subzero-rolled samples at low reduction (20%), while only a gradual increase of α′-martensite in cold-rolled samples took place with the increasing rolling reduction. Results from electron back-scattered diffraction indicate that annealing of cold-rolled samples produces finer recrystallized grains with increasing rolling reduction, while the predominant formation of α′-martensite in subzero-rolled microstructures is believed to have strong effect on the production of similar grain size upon annealing. Twin-related Σ3 boundaries were formed during annealing with maximum fraction of 53%. These boundaries become longer, straighter, and less incorporated into grain boundary network with the increasing rolling reduction and/or using subzero rolling, demonstrating an indirect mechanism of grain boundary engineering. Also, annealing caused scattering around the rolling texture components (Brass, Goss, S, and Copper) and the recrystallization textures become more random with the increasing rolling reduction and/or using subzero rolling. Nevertheless, recrystallization textures of samples reduced by 60% show formation of Cube and Dillamore orientations and strengthening of Brass orientation. This is thought to contribute to the enhancement of the tensile strength and microhardness of annealed samples.