Evolution of grain boundaries and subboundaries in stainless steel during dynamic recrystallization

The dynamic recrystallization (DRX) niicrostructures were studied in a 304-type stainless steel deformed at temperatures from 1023 K to 1223 K and at a strain rate of about 10(-3) s(-1). Both the dynamic grain size and the dynamic subgrain size were shown to depend on deformation conditions, and they could be expressed by different power-law functions of flow stresses. The subgrain size was related to the flow stress with a size exponent of about -1.0, while the grain size exponent was about -0.7. With increasing the deformation temperature, the fraction of the high-angle grain boundaries against all the strain-induced (sub)boundaries decreased from about 70% at 1023 K to 40% at 1223 K. The deformation microstructures are discussed in some detail with reference to the mechanisms of microstructure evolution that operated upon DRX.