Controlling the microstructure and mechanical properties of austenitic stainless steel by reversion of strain-induced martensite and recrystallization of retained austenite

Microstructural evolution during annealing of AISI 304 austenitic stainless steel following cold rolling was evaluated. It was revealed that three annealing stages are available: Reversion of martensite to austenite, recrystallization of the retained austenite, and grain growth. Reversion of martensite to austenite resulted to the development of an ultrafine grained microstructure. However, the recrystallization of the retained austenite postponed the formation of an equiaxed microstructure, during which, the fine austenite grains become coarser and a microstructure with average grain size between 1 and 2 µm was obtained. Evaluation of mechanical properties revealed that the reversion of martensite to austenite and the resultant grain refinement enhanced the tensile strength by 40%. Moreover, further annealing for the occurrence of the recrystallization in the retained austenite to obtain an equiaxed microstructure resulted in the decline of tensile strength and enhancement of ductility. In this way, it is possible to control the microstructure and mechanical properties of austenitic stainless steels.