Residual stress relaxation considering microstructure evolution in heat treatment of metallic thin-walled part

Abstract The forming-induced residual stress of metallic parts could cause undesired deformation in the final machining process, especially for the thin-walled parts. Therefore, heat treatment is essential to release the residual stress prior to machining. This study investigates the residual stress change of a forged pure iron part in annealing heat treatment and material removal processes. A modified creep constitutive model with the consideration of microstructure evolution was established to describe the residual stress relaxation in the annealing. Stress relaxation tests were conducted to calibrate the material constants. This constitutive model was then implemented into the finite element model of annealing for the cold-forged semi-spherical shell. The residual stress and the grain size of the shell were predicted at different heating temperatures. The semi-spherical shells were machined to the final thin-walled parts, and the deformation owing to the residual stress release was measured and compared to the simulation results. The heating temperature was determined aiming to minimize the machining-induced deformation as well as to ensure the microstructure. This study could provide guidance to the elimination of the residual stress and the improvement of the geometrical accuracy for thin-walled parts in the machining process.