Residual stress formation in DED-Arc manufactured high strength low alloy steel thin-walled structures with solid-state phase transformations

Abstract Directed Energy Deposition-Arc (DED-Arc) processes create residual stresses in the material due to their nonuniform thermal gradients. These residual stresses interact with the in-service loads and could negatively impact the material integrity. To understand and mitigate the negative effects of these stresses, in this study, a thin-walled structure out of a high strength low alloy (HSLA) steel was manufactured by DED-Arc process. The formation of residual stresses was studied with neutron diffraction at the centerline of the structure. To incorporate the effects of martensitic phase transformation on the residual stress formation, the microstructure of the material was studied using electron and optical microscopy. Also, the phase fractions were calculated using image segmentation methods. Furthermore, thermodynamics calculations were performed to understand the kinetics of the phase changes. The results show that the structure follows a tensile-compressive-tensile-compressive residual stress regime in the travel direction by moving from the lower side of the substrate to the top side of the thin-walled structure. The main influencing factors in the formation of these stresses are the volume expansion due to martensitic and bainitic phase transformations, contraction due to cooling of the hot material, and bending of the structure due to the interaction between tensile and compressive stresses at different heights of the part.