Flow localisation behaviour of AISI 304L austenitic stainless steel in warm and hot working regions

Abstract

A workability test which evaluates the susceptibility of a material to flow localisation during forging was used to identify the processing parameters, namely, strain rate and temperature at which the tendency of the material to undergo localised flow is enhanced. The tendency of a material to undergo localised flow was measured via a previously proposed empirical parameter, namely, percentage distributed gauge volume (DGV). Low values of DGV are usually associated with localised plastic flow and conditions which favour the formation of shear bands. Tests were carried out on AISI 304L austenitic stainless steel in the temperature range 673–1423–K and at nominal strain rates of 0·3, 100, and 200 s−1. A hydraulic press and a forge hammer were used to achieve the required strain rates. At 0·3 s−1 the DGV decreased with increasing temperature up to 1273 K and an increase was observed at 1423 K. In contrast, at high strain rates the DGV decreased to very low values at 1423 K. Microstructural observations and microhardness measurements on the specimens having low values of DGV confirmed the occurrence of localised deformation. At 0·3 s−1 and temperatures in the range 1123–1273 K the flow localisation was associated with dynamic recovery and dynamic recrystallisation. At high strain rates and at 1423 K flow localisation was due to the synergistic effect of adiabatic heating and dynamic recrystallisation.MST/1669