Effects of stress-relief heat treatment on the microstructure and fatigue property of a laser additive manufactured 12CrNi2 low alloy steel

Abstract

In this study, the impact of stress-relief heat treatment on the microstructure and fatigue property of a laser melting deposited (LMD) 12CrNi2 low alloy steel was analyzed. Microstructural evolution of processed LMD 12CrNi2 steel by heat treatment was studied using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), aiming to establish a rational microstructure-fatigue property relationship. The results showed that the main phase of the samples before and after heat treatment was α-Fe phase, whereas the lattice parameter slightly decreased after annealing, as a result of stress relief and carbide formation in the heat-treated samples. Meanwhile, the increase of the hard and diffusely distributed carbides inside the matrix was the main contributor for the higher material strength. Based on the EBSD analysis, the heat treatment decreased grain boundary misorientation leading to a corresponding reduction in the dislocation density, and increased the content of high-angle grain boundaries (HAGBs) promoting the toughness of the material. Furthermore, Schmid factor results revealed that the heat-treated samples exhibited a relatively high ductility resulting from the activation for more slip systems during the cyclic deformation. The stress-relief heat treatment significantly improved the fatigue performance of samples, which was attributed to the enhanced strength and ductility owing to the related microstructure change and the relief of residual stresses.