Effect of niobium on massive transformation in ultra low carbon steels: A solute drag treatment

The effect of Nb on the gamma --> alpha transformation in ultra low carbon steels is examined experimentally and theoretically. It is shown that there are two modes of the massive transformation. One of them is heavily influenced by the solute drag effect of Nb. This is confirmed by a calculation based on a new model for treating the solute drag effect. The calculation result shows that the critical temperature between these two massive transformations depends mainly on the segregation tendency of Nb into the phase interface and the velocity diminished by the solute drag depends on the diffusivity of Nb in the phase interface. Copyright (C) 1996 Acta Metallurgica Inc.