Microstructural evolution of a 304-type austenitic stainless steel during rolling at temperatures of 773–1273 K

The structural changes leading to grain refinement in a 304-type austenitic stainless steel subjected to warm caliber rolling over a wide temperature range of 773–1273 K were studied. The development of a new ultrafine-grained structure during rolling primarily resulted from continuous dynamic recrystallization. Two deformation domains were recognized that exhibit different recrystallization processes. In the high-temperature deformation domain, the majority of new strain-induced grain boundaries developed homogeneously through largely uniform formation of a network of deformation sub-boundaries, the misorientations of which attained values of high-angle grain boundaries during deformation. In this case, the kinetics of the microstructural evolution depended on dynamic recovery, which accelerated with increasing deformation temperature. In contrast, the development of new strain-induced grain boundaries was primarily associated with deformation microbanding in the low-temperature deformation domain. The development of deformation microbands resulted from strain localization and was promoted by a decrease in the deformation temperature. Therefore, the opposite temperature effect on the contribution of different structural mechanisms to new grain development led to temperature-independent kinetics of grain refinement for a wide range of warm working.