Warm Deformation and Dynamic Strain Aging of a Nb-Cr Microalloyed Low-Carbon Steel

Abstract

Warm rolling can be a cost-effective technique to achieve an excellent combination of strength and deep drawing properties in low-carbon steels, as the formation of intergranular shear bands (SBs) induces a {111} recrystallizing texture. However, the formation of SBs can be significantly suppressed due to dynamic strain aging (DSA). Therefore, it is necessary to confirm the temperature where DSA occurs and further investigate its physical mechanism. In this study, compression tests were conducted on Nb-Cr modified low-carbon steels from 250 °C to 650 °C at two true strains of 0.43 and 0.92. The flow stress behavior was carefully analyzed, and the microstructure evolution was investigated by transmission electron microscope (TEM). With an increase in the deformation temperature, DSA occurred at temperatures between 250 °C and 450 °C, and an obviously serrated plastic flow was observed at 350 °C. The TEM results revealed planar dislocations at this stage, resulting from the interactions between the mobile dislocations and solute atoms or nanosized precipitates. When the temperature reached 450 °C and above, the DSA disappeared, the size of the dislocation cells increased, and the dynamic recovery led to the formation of subgrains.