Temperature Dependence of Tensile Behaviors of Nitrogen-Alloyed Austenitic Stainless Steels

The temperature dependence of tensile behaviors of two nitrogen-alloyed austenitic stainless steels, an annealed 316LN steel and a high-nitrogen austenitic stainless steel (Fe-Cr-Mn-0.66% N), was investigated by tensile test at different temperatures from 293 K down to 77 K. It was found that strength of the two steels increased with decrease of temperature. With a decrease in temperature, the uniform elongation increased for the 316LN steel, whereas it increased followed by a decrease for the high-nitrogen steel. A three-stage hardening behavior occurred in the 316LN steel, but not in the high-nitrogen steel, with decrease of temperature. The strain-induced martensite transformation in the 316LN steel could retard void nucleation and increase the strain-hardening rate, resulting in much higher tensile stress and higher uniform elongation of 316LN steel. It was analyzed that stacking fault energy of the high-nitrogen steel decreased with decrease of temperature, which promoted the twinning and planar slipping in the steel, and resulted in brittle fracture at cryogenic temperatures.