Ferritic-martensitic structure in steel hardenable by copper precipitation

Abstract

The copper precipitation offers possibility of effective and easily achievable ferrite strengthening. There is reported yield point rise by 150 MPa thanks to formation of nanometric copper precipitates in ferrite for Cu content 1.5 wt.%. Such rise of yield strength is most significant for soft and ductile materials, containing free ferrite. Ferritic-martensitic dual steels are example of such material. They are widely used for their favourable combination of strength and ductility. Their yield strength is defined by the soft phase, the ferrite. Ferrite strengthening in these steels is achieved mainly by grain refinement and by solution strengthening caused by substitutional alloying elements. This article describes preparation of dual phase structure in 0.2% C steel alloyed by Cu, Mn, Ti and B. Dual phase structure was prepared by controlled rolling with rolling finishing temperatures in the intercritical region. Samples were analysed by light and scanning electron microscopy. Hardness was measured and tensile tests were performed.