Deformation and phase transformation mechanisms of 40Cr10Si2Mo steel during hot compression

Thermo-mechanical experiments on martensitic heat-resistant 40Cr10Si2Mo steel were conducted using a Gleeble simulator in temperature and strain rate ranges of 1073–1373 K and 0.1–20 s, respectively. Processing maps were developed and correlated with deformed microstructures based on the dynamic material model theory. The analysis of the maps revealed that both applied temperature and strain rate had significant effects on the power dissipation efficiency and flow instability of the steel alloy. Electron backscatter diffraction analysis was also implemented to study the effect of deformation conditions on martensitic morphology. The results showed that higher temperatures and strain rates led to a fine martensitic packet, and the martensite lath increased in width at high temperatures. Two deformation domains, which exhibit different recrystallization processes, were recognized. The discontinuous dynamic recrystallization (DRX) mechanism in the low strain rate domain was characterized by the migration and growth of high-angle grains during straining. In contrast, in the high strain rate domain, the development of new grain boundaries is primarily associated with the deformation microbands in the low-temperature deformation domain. As the temperature increased, the high dislocation density accelerated the migration of the grain boundaries. Furthermore, the DRX mechanism changed from continuous DRX to post-DRX. This change in the DRX mechanism type was attributed to the time during which the sample remained high temperature after deformation.