Correlation of microscopic structures to the strain rate hardening of SPCC steel

The high strain rate properties of steel have been studied for accurate crashworthiness of vehicles. The mechanical properties at high strain rates show different characteristics from those at the quasi-static state. In order to seek for the physical phenomenon of the strain rate hardening, a microscopic investigation has been conducted for the texture evolution and dislocation behavior of steel. Tensile tests were performed at strain rates ranged from 0.001/s to 100/s, which is the common range in practical vehicle crashes to investigate the microstructural variation and dislocation behavior. According to experimental results of the EBSD and TEM experiment, the texture evolution does not develop remarkably with the variation in strain rates, while dislocation structure and behavior investigated by TEM experiments show significant difference with the variation in strain rates. The change in the dislocation structure, behavior, and density with the variation of strain rates clearly explains the mechanism of the strain rate hardening showing that round half-loop dislocations are replaced by straight and crossing dislocations and then by cell structured dislocations.