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

Abstract

Hot deformation behaviors and dynamic softening mechanisms of the 7Mo super-austenitic stainless steel (SASS) were studied in the temperature range of 1000–1200 °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 °C and strain rate range of 0.001–0.07 s−1, and temperature range of 1050–1200 °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.

Keywords

• 7Mo super-austenitic stainless steel
• Hot deformation behaviors
• Dynamic softening mechanism
• Continuous dynamic recrystallization
• Deformation microbands