Effects of electric current pulses on mechanical properties and microstructures of as-quenched medium carbon steel

The effects of electric current pulse (ECP) on the mechanical properties and the microstructures of as-quenched medium carbon steel specimens were investigated. After ECP treatment, hardness, tensile property, residual stresses, microstructures and dislocation density were evaluated. The experimental results showed that the lath-shaped martensite structure remained identical, and the width and grain orientation did not change compared to the original specimens, and residual stresses and dislocation density decreased. The tensile strength increased greatly with a little decrease of hardness after ECP treatment. The mechanisms of the effects of ECP on these properties were analyzed in depth. The decrease of dislocation density induced the decrease of residual stresses, and the decreases of residual stresses and dislocation density resulted in the increase of tensile strength. The Joule heat due to ECP primarily affects the dislocation dynamics, and the electron drag force has a minimal effect. During ECP treatment, the increase of temperature due to the Joule heat and the large quenching residual stresses will promote the activation rate of dislocations. After being activated, the dislocations glide or climb and annihilate, which results in the decreases of dislocation density and residual stresses. In this case, the tensile strength increased.