Solid-state phase transformation-induced residual stress in selective laser melting of martensitic stainless steel

Selective laser melting (SLM) is a promising technique for fabricating parts with complex features. Residual stress in SLM is key challenge in terms of the geometric accuracy and performance of a part. In this study, we investigated the effect of solid-state phase transformation on the residual stress in the SLM of martensitic stainless steel. A multi-scale finite-element (FE) thermo-mechanical model considering phase transformation was developed to predict the residual stress distribution and part deformation. Free dilatometry tests and uniaxial tensile tests were performed on austenitic and martensitic samples to obtain the mechanical property change, volumetric change, and transformation-induced plasticity during the phase transformation. The SLM process of a cantilever part was simulated using the developed FE model, and the predictive residual stress and deformation of the cantilever were studied. Neutron diffraction and X-ray diffraction were used to verify the predictive residual stress. It was found that the phase transformation had a dominant effect on the stress distribution, thus, the deformation of the SLMed part. Owing to the phase transformation, a high residual stress gradient existed in the build direction, with compressive stress on the surface and tensile stress inside the part.