Instability map for cold and warm working of as-cast 304 stainless steel

Abstract

The deformation characteristics of as-cast 304 stainless steel under compression in the temperature range 20–600°C and strain rate range 0.001–100 s⁻¹ have been studied with a view to characterizing the flow instabilities occurring in the microstructure. At strain rates of less than 0.05 s⁻¹, as-cast 304 stainless steel exhibits flow localization in the temperature range 20–600°C, whereas dynamic strain ageing occurs at intermediate temperatures and below 5 s⁻¹. At room temperatures and strain rates of less than 0.05 s⁻¹, martensite formation is observed. To avoid the above microstructural instabilities warm working should be carried out at strain rates greater than 10 s⁻¹ in the temperature range 400–600°C and cold working could be done in the range of about 0.05–0.8 s⁻¹. The continuum criterion developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all of the above instability features.