Effect of Aging Process on the Strain Rate Sensitivity in V-Containing TWIP Steel

Abstract

The dynamic tensile behavior of the twinning-induced plasticity (TWIP) steel with the vanadium carbide is investigated at different strain rates of 10−4, 10−3, 10−2 and 0.05 s−1. Microstructure characterization, carried out using back scatter electron diffraction (EBSD) and transmission electron microscopy (TEM), shows a homogeneous face center cubic structured matrix with uniformly dispersed vanadium carbide. The vanadium carbide is controlled by the aging temperature and time. The best comprehensive mechanical properties are achieved when the tested steel is aged at 550 °C for 5 h. With the increase of strain rate, the tensile strength and work hardening rate decrease, and the tested material shows negative strain rate sensitivity. This would be due to an increase in stacking fault energy caused by temperature rise by adiabatic heating, which must suppress the formation of twinning. On the other hand, the strain rate sensitivity is affected by dynamic strain aging (DSA). With the increase of strain rate, the DSA weakens, which causes negative strain rate sensitivity. The tensile strength and strain rate sensitivity value both increase first and then decrease with the increase of vanadium carbide size. This is because the tensile strength is mainly affected by the vanadium carbide. In addition to the vanadium carbide, the strain rate sensitivity is also affected by the amount of solute atom (V and C) during the dynamic strain aging process.