Correlating temperature-dependent stacking fault energy and in-situ bulk deformation behavior for a metastable austenitic stainless steel

Abstract

In-situ high-energy synchrotron X-ray diffraction experiments during uniaxial tensile loading are performed to investigate the effect of temperature (25, 45 and 70 °C) on the deformation behavior of a 301 metastable austenitic stainless steel. The micromechanical behavior of the steel at the three deformation temperatures is correlated with the stacking fault energy (γSF) experimentally determined through the same in-situ X-ray experiments. The applied measurements provide a unique possibility to directly interrogate the temperature-dependent γSF in relation to the active bulk deformation mechanism in a metastable austenitic stainless steel. The determined γSF is 9.4 ± 1.7 mJ m−2 at 25 °C, 13.4 ± 1.9 mJ m−2 at 45 °C and 25.0 ± 1.1 mJ m−2 at 70 °C. This relatively minor change of γSF and temperature causes a significant change of the dominant deformation mechanism in the alloy. At room temperature (25 °C) significant amounts of stacking faults form at 0.05 true strain, with subsequent formation of large fractions of deformation-induced α′- and ε-martensite, 0.4 and 0.05, at 0.4 true strain, respectively. With increasing temperature (45 °C) fewer stacking faults form at low strain and thereupon also smaller α′- and ε-martensite fractions form, 0.2 and 0.025, at 0.4 true strain, respectively. At the highest temperature (70 °C) plastic deformation primarily occurs by the generation and glide of perfect dislocations at low strain, while at higher strain these dislocations dissociate to form stacking faults. The α′-martensite fraction formed is significantly less at 70 °C reaching 0.1 at 0.4 strain, whilst ε-martensite is not found to form at any strain at this temperature. The temperature-dependent mechanical behavior of the alloy is consistent with the observed dominant deformation mechanisms; the strong work hardening from the TRIP effect at low temperature, and low γSF, decreases significantly with increasing temperature, and γSF.