Enhanced Mechanical Properties of a Novel High-Nitrogen Cr-Mn-Ni-Si Austenitic Stainless Steel via TWIP/TRIP Effects

Temperature- and strain-rate-dependent mechanical properties of a high-nitrogen austenitic stainless steel containing smaller amounts of nickel than conventional austenitic nickel-chromium stainless steels were investigated with special attention to the formation of martensite or mechanical twins during plastic deformation (TWIP/TRIP effect). After recrystallization treatment at 1050 A degrees C for 0.5 hour, an equiaxed fully austenitic microstructure possessing annealing twins was observed. Tensile tests were carried out at strain rates ranging from 10(-5) to 10(-2) s(-1) in the temperature range from -196 A degrees C to 400 A degrees C. Deformation-induced austenite-to-martensite transformation occurred at temperatures below 0 A degrees C. From room temperature up to 200 A degrees C, plastic deformation is controlled by dislocation glide and mechanical twinning. At temperatures above 200 A degrees C, no deformation-induced structural changes were observed. The formations of bcc alpha'-martensite and hcp epsilon-martensite, or twins during plastic deformation, were analyzed by optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction.