Dynamic behaviour of 304 stainless steel during high Z deformation

The deformation behaviour of 304 stainless steel was investigated over a range of strain rates spanning those from typical laboratory conditions through to those more commonly experienced in industry. This study examines the effect of the Zener–Hollomon (Z) parameter on the shape of the deformation flow curves. At Z values typical of laboratory experiments the flow curves display a behaviour indicative of dynamic recrystallization (DRX). A clear peak can be seen in the curve, but as the Z value increases (increasing strain rate/decreasing temperature) the shape of the curve changes to a ‘flat-top’ behaviour which has traditionally been used to indicate that no DRX is occurring and that dynamic recovery (DRV) is the only softening mechanism operating. Examination of the corresponding work hardening curves (θ = δσ/δɛ) and deformation microstructures suggests that some level of dynamic recrystallization has occurred. The results suggest that at the higher strain rates the main mechanism for DRX is only the formation from prior austenite grain boundary bulges and that subsequent layers of DRX grains are very difficult to form. The overall deformation textures were also found to be independent of the strain rate.