Simulating Distortion and Residual Stresses in Carburized Thin Strips

This paper illustrates the application of a new multiphase material model for simulating distortion and residual stresses in carburized and quenched gear steels. Simulation is focused on thin, metallic strips that are heat treated to introduce a through-thickness carbon gradient. Because the material properties are strongly dependent on the carbon content, quenching causes significant transverse out-of-plane distortion. The material model accounts for a multiphase alloy structure where inelasticity in the individual phases is temperature and rate dependent. The model is fit to an extensive matrix of experimental data for low carbon steels (0.2–0.8 percent) whose transformation kinetics and mechanical response are similar to 4023 and 4620 alloys used in experiments. While residual stress data are limited, reasonable agreement with X-ray diffraction measurements was obtained. Comparisons of transverse deflections predicted numerically showed excellent agreement with those measured experimentally for all five thicknesses reported. Accurate transformation and lattice carburization strains are critical to correctly predict the sense and magnitude of these transverse distortions and in-plane residual stresses.