Micromechanisms of deformation of an austenoferritic duplex stainless steel

Slip transmission through austenite-ferrite coherent interfaces is studied using transmission electron microscopy (TEM) and in-situ TEM at room temperature and high temperatures, on as-received and on aged specimens. It is shown that austenite deforms first, and that slip transmission from austenite to ferrite is effective only for the slip systems which are shared by the two phases. Deformation in ferrite is fairly homogeneous in the as-received state, but becomes quite localized in the aged material. In this case, sluggish and jerky glide of short edge dislocations coming from the interface generates long screw dislocations, which experience a strong Peierls frictional stress. A simple model is proposed for strain localization, which qualitatively accounts for slip band separation and interfacial step heights as a function of temperature, in terms of the amount of hardening due to spinodal unmixing of aged ferrite and of the variations with temperature in both the yield stress and the work-hardening rate of ferrite.