Endurance Life and Deformation Behavior under Thermo-mechanical Fatigue of Nb-added Heat Resistant Austenitic Stainless Steel

Abstract

Thermomechanical fatigue (TMF) behavior of heat resistant austenitic stainless steel was evaluated in the temperature range from 100°C to peak temperatures of 600 to 800°C; The fatigue lives under TMF conditions were plotted against the plastic strain range and the dissipated energy per cycle. In the expression of the inelastic strain range versus fatigue life, the TMF data obtained at different temperature ranges were located close to a single line with a small deviation; however, when the dissipated energy per cycle, calculated from the area of the stress-strain hysteresis loops at the half of the fatigue life, was plotted against the fatigue life, the data showed greater scattering than the TMF life against the inelastic strain range. A noticeable stress relaxation in the stress-strain hysteresis curve took place at the peak temperatures higher than 700°C, but all specimens in this study exhibited cyclic hardening behavior with TMF cycles. Recrystallization occurred during the TMF cycle concurrent with the formation of fine subgrains in the recrystallized region, which is considered to cause the cyclic hardening of the steel. (Received March 29, 2011)