Effects of niobium on phase transformations from austenite to ferrite in low carbon steels

Niobium is a widely used microalloying element in many steel products, e.g. plates, strip, sections and linepipe. Niobium has important effects on transformation behaviour, grain size refinement and precipitation strengthening during hot rolling and subsequent cooling, with even a low content of niobium having a strong effect on the transformation rate from austenite to ferrite. The purpose of this research was to accurately characterise and quantify the effects of solute niobium atoms and niobium carbo-nitride precipitates on phase transformations from austenite and ferrite, and to incorporate these effects into metallurgical models to predict the transformation behaviour and microstructure of niobium containing steels, which can benefit industry through their use of the models to optimise processing conditions. [Continues.]