Effect of Carbide Precipitation on “Precipitation Plasticity” and Residual Stress during Tempering

Abstract

Materials with residual stress can experience irreversible plastic strains as carbides precipitate during the tempering process, thereby relaxing the residual stress. In previous studies, this plastic behavior is named “precipitation plasticity.” Although precipitation plasticity plays a key role in the relaxation of the residual stress, the micromechanism involved is not yet elucidated. Here in this study, experiments are performed on low‐carbon steel to study precipitation plasticity and the residual stress during tempering. The results show that precipitation plasticity is mainly produced by the generation of interfacial vacancies at the carbide–matrix interface and the diffusion and evolution of these vacancies under temperature and stress fields. Two precipitation plasticity regimes are observed, namely, Precipitation Plasticity I, which is associated with vacancy diffusion, and Precipitation Plasticity II, which is associated with dislocation proliferation. Precipitation Plasticity I is found to be controlled by the volume mismatch and carbide size and is the main cause of residual stress relaxation. The finer and more dispersed the carbide precipitates are, the more significant the precipitation plasticity is. Precipitation Plasticity II causes a slight increase in the residual stress, which, however, is considerably smaller than the stress relaxation corresponding to Precipitation Plasticity I.