Relationship between processing, microstructure, and properties in controlled rolled 0·45%V steel

Abstract

The microstructures of a 0·45%V controlled rolled steel, subjected to various processing conditions, have been characterized by light and electron microscopy in order to correlate changes in processing with microstructure and mechnical properties. It is found that vanadium carbide can precipitate in austenite during controlled rolling to the extent that austenite recrystallization is prevented and fine grained structures are produced. Substructured, carbide free, ferrite forms during final rolling, and carbon is rejected into the surrounding austenite. The subsequent transformation to ferrite can be accompanied by interphase precipitation of carbide in a relatively dislocation free ferrite. Austenite remaining after the interphase reaction has, by virtue of its vanadium content, sufficient hardenability to allow the formation of a hard carbon rich microconstituent on subsequent cooling. This constituent is responsible for the continuous yielding behaviour of the steel. The resultant microstructures are very similar to those of the Mn–Mo–Nb controlled rolled steels. Different processing conditions lead to variations in the relative amounts and grain size of the various microconstituents, which correlate well with variations in strength and toughness.