Multi-scale residual stress prediction for selective laser melting of high strength steel considering solid-state phase transformation

Abstract The complex metallurgical processes of high strength steel making it difficult to accurately predict the residual stress in laser additive manufacturing, especially for part scale parts. To solve this problem, a multi-scale model considering solid-state phase transformation (SSPT) is proposed to predict thermal, residual stress evolution and distribution for the selective laser melting (SLM) process of high strength tool steel. In 3D finite-element-method thermo-metallurgical-mechanical model, the Kamamoto equation and Koistinen-Marburger equation are used to predict the austenite and martensite phase transformation, respectively. The temperature cycle and thermal behavior are analyzed, and the effects of phase properties transition, transformation-induced volume change and plasticity on residual stress are discussed in detail. The residual stress spatial distribution of multi-layer is obtained. Simulations show that the SSPT has a significant effect on the residual stress evolution in the SLM of high strength steel, considering the influence of phase transformation can effectively reduce tensile residual stress. The thermo-metallurgical-mechanical model is then applied to obtain the inherent strain. The inherent strain method is used to predict the residual stress of the part scale models. Compared with the experimental data, the simulated residual stress shows the same variation trend, which indicates that the proposed multi-scale model can predict residual stress in SLM of high strength steel more accurately and efficiently.