Dynamic Softening Mechanisms in 304 Austenitic Stainless Steel

Dynamic softening mechanisms have been determined through analysis of continuous torsion flow curves of both as-cast and worked type 304 stainless steel in the range 1200–900°C and 0.1 to 5.0 s−1. The critical stress and strain for subgrain formation and for dynamic recrystallization (DRX) initiation were determined from changes in slope of the strain hardening-stress curves. The flow curves peak at approximately 30% DRX and soften to a steady state regime at 99% DRX. The rate of softening can be described by means of the Avrami equation with a k value of 1.27. The transition from multiple peak grain coarsening to single peak grain refinement behavior has been determined. While the DRX grain size is a linear function of the steady state flow stress with a power of –1.23, the subgrain diameter function has a power of −1.