Residual stress mapping in additively manufactured steel mould parts using asymmetric and multiple cuts contour method

Abstract

The distribution of residual stress in additively manufactured (AM) complex structures can be intricate, exhibiting large gradients. Accurate measurements with high spatial resolution at significant depths are crucial for understanding the residual stress distribution in AM parts. In this study, the contour method, with asymmetric and multiple cuts, is employed to map residual stresses on various cross-sections of AM steel mould parts with inner channels. The resulting residual stress maps are compared for different states: as-built, shot-peened, and shot-peened plus heat-treated, in order to quantify the stress relaxation effect of each processing step. In the as-built state, elevated levels of tensile stress are observed around the perimeter, with a substantial stress gradient throughout the depth. Compressive stresses are distributed over a larger interior region, but with lower magnitudes compared to the tensile stresses. Upon shot-peening, the tensile stresses are reduced by approximately 300 MPa around the perimeter, with limited relaxation up to a depth of 1 mm compared to the as-built state. In the shot-peened and heat-treated state, a more significant stress relaxation is observed across the cross-sections. The maximum relaxation in tensile stress reaches approximately 1200 MPa, while the maximum compressive stress relaxation amounts to around 500 MPa, both compared to the as-built state. The stress maps effectively identify regions experiencing significant stress states, and the two-dimensional comparisons between different stress states provide crucial information for enhancing and validating AM models and processing techniques.