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

Abstract

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 °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 °C to 400 °C. Deformation-induced austenite-to-martensite transformation occurred at temperatures below 0 °C. From room temperature up to 200 °C, plastic deformation is controlled by dislocation glide and mechanical twinning. At temperatures above 200 °C, no deformation-induced structural changes were observed. The formations of bcc α′-martensite and hcp ε-martensite, or twins during plastic deformation, were analyzed by optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction.