Effect of cryogenic deformation on microstructure and mechanical properties of 304 austenitic stainless steel

Abstract

304 austenitic stainless steel plates have been deformed (10 to 40%) by multi-pass cold rolling incorporating soaking at 0°C and −196°C after each pass with an aim to correlate the microstructure and mechanical properties under cold/cryogenically deformed conditions. Characterisation of phase constituents, microstructure and mechanical properties of such steel specimens has been conducted after processing under different schedules. Rolling of the investigated steel at near cryogenic temperature results into the formation of extended stacking faults, ε-martensite and α′-martensite in contrast to the formation of homogeneous dislocation structure along with α′-martensite in the samples rolled at 0°C, which can be correlated with temperature dependent stacking fault energy. EBSD phase analysis reveals 46.3% and 69.2% α′-martensite in the austenitic matrix for 10% and 20% deformation at −196°C, respectively. Deformation twins are evident in all the samples rolled at 0°C as well as −196°C. 40% cold deformation at 0°C leads to high strength (1225MPa) and 13% total elongation, whereas comparatively lower 10–20% deformation at −196°C leads to higher level of strength (1306–1589MPa) with 15–9% elongation due to the formation of the higher volume fraction of strain induced martensite (ε/α′).