Hot deformation behaviors and dynamic softening mechanisms of 7Mo super-austenitic stainless steel with high stacking fault energy

Hot deformation behaviors and dynamic softening mechanisms of the 7Mo super-austenitic stainless steel (SASS) were studied in the temperature range of 1000-1200 degrees C and stain rate of 0.001-10 s-1. It is found the optimum windows of hot deformation are mainly in the temperature range of 1030-1200 degrees C and strain rate range of 0.001-0.07 s-1, and temperature range of 1050-1200 degrees C and strain rate of 10 s-1. The apparent activation energy of 7Mo SASS has reached 558.9 kJ mol-1, which is about 100-180 kJ mol-1 larger than ordinary austenitic stainless steels and about 60-95 kJ mol-1 larger than 4.5-6 wt.% Mo super-austenitic stainless steels. Due to high stacking fault energy (SFE, 161.2 mJ m-2), planar gliding of dislocations is the main deformation mechanism of 7Mo SASS. As a result, dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) are easy to occur and play dominant roles in dynamic softening mechanism of this steel. In addition, at strain rate of 10 s-1, especially at low temperature, the appearance of microbands (MBs) significantly promotes CDRX. Large initial sigma precipitates and micron-sized dynamic sigma precipitates also promote CDRX through the particle-stimulated nucleation (PSN) mechanism.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).