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

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2020-07, Vol.791, p.139738, Article 139738
• Main Authors: Cui, X., Zhang, S., Wang, C., Zhang, C.H., Chen, J., Zhang, J.B.
• Format: Article
• Language: English
• Subjects: 12CrNi2 low alloy steel; Carbides; Dislocation density; Ductility; Electron backscatter diffraction; Fatigue property; Grain boundaries; Heat treating; Heat treatment; Laser additive manufacturing; Laser beam melting; Low alloy steels; Materials fatigue; Metal fatigue; Microstructure; Misalignment; Residual stress; Thermal cycling
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.139738

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. •Laser melting deposited 12CrNi2 samples were heat treated and characterized.•Microstructure features were correlated with fatigue behaviour.•Heat treatment improved the fatigue strength from 350 MPa to 410 MPa.•The strengthening was attributed to the unique heat-treated microstructure.