Effect of Residual Stress Distribution on the Formation, Growth and Coalescence of Voids of 27Cr White Cast Iron under Impact Loading

Abstract

The present study shows that effect of impact load on microstructural feature in 27Cr white cast iron alloy, which is destabilized at 1150°C for 3 hour holding. The specimen is received with a microstructure consisting of ductile matrix (57% retained austenite) and amount of dispersed secondary. The residual stresses distribution in the alloy as a function of the impact load, they localized around the eutectic carbides and eutectic carbides, at defect positions. This distribution tends to decrease in the impact loading direction. The dislocations are formed in alloy as a result of the concentration stress, which caused by impact load. High stress concentration promotes the interaction between dislocations and these dislocations tend to pile-up at grain boundaries. In this study, the helical dislocations are observed in the stress concentration areas. The voids are formed by the pile-up of dislocations. The diameter of voids can be from several tens nanometers to 500 nanometers and depending on the applied load. When the voids expand (exceed 500 nm diameter), the ligament around void is thinner and leads to an increase in the deformation region between voids. As a consequence, the voids coalesce by formation the necking of the ligament between two voids to form a micro-crack.