A three-dimensional model for the development of the microstructure in steel during slow cooling

A general three-dimensional model for the development of microstructure in metals by diffusion-controlled processes has been constructed. The model ha s been applied to the austenite (gamma-Fe) to ferrite (alpha-Fe) phase tran sformation in plain-carbon steels. Starting from a Voronoi construction for the austenite grains, the ferrite is assumed to nucleate at the corners of the original austenite grains. Subsequently, the growth of the ferrite gra ins is assumed to be radial and to fulfil the conditions of local equilibri um at the ferrite-austenite interface. The development of the ferrite fract ion, the ferrite grain size, and the number of active nucleation sites have been evaluated as a function of time during continuous cooling. The influe nce of the nucleation rate, the growth rate, the nucleus density, the cooli ng rate, and the carbon concentration on the development of the microstruct ure is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.