Formation and thermal fatigue properties of fine-grained heat affected zone on cast-hot-working-die steel after electropulsing stimulation with high current density

Abstract

The fatigue crack propagation behaviors of cast-hot-working die (CHWD) steel untreated and treated by electropulsing stimulation with different current densities were investigated in the present study. The elliptical heat affected zone (HAZ) was formed ahead of specimen notch tip due to the concentrating heat release induced by current bypassing and concentrating effect. The acreages of specimen HAZs were gradually enlarged because of the more heat energy input by elevating current density of electropulsing stimulation. The grain refinement and dislocation density increase in the specimen HAZs were enhanced by elevating the current density of electropulsing stimulation, which inevitably resulted in the improvement on the HAZ mechanical properties and the enhance of fatigue resistance. In addition, the induced compressive stress by electropulsing stimulation could decrease the peak value of tensile stress forming in the thermal fatigue process, which also enhanced the thermal fatigue resistance. Consequently, the resistance to thermal fatigue of CHWD steel was enhanced by grain refinement, dislocation density increase and induced compressive stress after electropulsing stimulation with high current density. © 2008 ISIJ.