The sigmoidal strain hardening behaviour of a metastable AISI 301LN austenitic stainless steel as a function of temperature

Mathematical relationships linking flow stress to the deformation temperature have been developed describing the strain hardening behaviour of AISI 301LN metastable austenite steel at temperatures up to 75 degrees C. Sigmoidal flow stress relationships were dominant at most temperatures but reduced to Hollomon-type equations at a temperature of 90 degrees C and above. The observed sigmoidal behaviour was shown to be driven by pronounced strain-induced martensitic transformation, while the change to a Hollomon - type behaviour at the higher temperatures is believed to be due to absence of significant amounts of strain-induced martensite at the higher temperatures. With increasing deformation temperature, the deformation mechanism is shown to be a mixture of Transformation Induced Plasticity (TRIP) and Twinning Induced Plasticity (TWIP), with the latter mechanism being dominant at high temperatures as indicated by Stacking Fault Energy (SFE) calculations carried out as a function of temperature. The variation of the instantaneous strain-hardening exponent, n as a function of applied strain and the influence on the strength coefficient, K, as a function of temperature have been studied for the full temperature range and interpreted.