Plastic deformation and dissolution of ε-Cu particles by cold rolling in an over-aged particle dispersion strengthening Fe-2mass%Cu alloy

Deformation and dissolution behaviors are important characteristics of soft dispersion particles in steel to improve the deformability of high strength steel sheets by controlling the work hardening/softening and fracture processes associated with particle dispersion strengthening. In this study, the deformation and dissolution behaviors of ε-Cu precipitate particles in a ferrite matrix were investigated to understand how relatively soft dispersion particles influence mechanical responses of the steel compared to hard dispersion particles such as alloy carbides. 35 nm diameter nearly spherical ε-Cu particles were initially elongated along the rolling direction by cold rolling, and then these were partly dissolved into the ferrite matrix as the equivalent strain increased. The dissolution of the Cu particles was suggested to be caused by a dynamic partitioning of Cu atoms from the precipitates into the matrix by dislocation shearing at the particle tip sharpened by severe cold working. Simultaneously, the contribution of the ε-Cu particles to the dispersion strengthening appeared to be decreased with increasing dislocation density in the matrix during cold rolling. The dislocation density and other defects in the ε-Cu particles also increased and the particle/matrix interfaces were serrated or became indistinct as deformation progressed. The morphology, internal defects, and interface structure changes of fine dispersion particles and their correlation with mechanical responses of the alloy are discussed in reference to an identically processed, hard particles dispersed Fe-V binary alloy.