Two experimental 0.2C steels with 1 wt% and without Cu were studied. A dual ferritic-martensitic microstructure was prepared by controlled rolling and subsequent quenching. The heterogenous microstructure was obtained due to the severe cooling of the surface layer during the rolling process. The surface layer of the sheet had a significantly finer ferritic grain than the sheet's core. Mechanical properties of the core were not correlated to the Cu content, whereas the surface layer revealed Cu-related strengthening due to Cu precipitation. Rows of particles typical for interphase precipitation were observed in some of the ferrite grains of the Cu-containing sample. Mode of the ferrite growth from austenite has apparently a crucial role in Cu ability to rapidly precipitate in ferrite grain during or shortly after its formation.
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