MODELING OF REAUSTENITIZATION FROM THE PEARLITE STRUCTURE IN STEEL

A two-dimensional model has been developed for the description of the formation of austenite from lamellar pearlite in steel. The diffusion equation is solved in a small domain representative of a regular struc ture of lamellar pearlite. The solution is obtained using a finite ele ment method with a deforming mesh and a remeshing procedure. The main assumption of the model is the condition of local equilibrium at the i nterfaces, including the curvature contribution and mechanical equilib rium of surface tensions at the triple junction where the ferrite, aus tenite and cementite phases meet. The velocity of the interface is ded uced from a solute balance which involves the concentration given by t he phase diagram modified by the Gibbs-Thomson effect. The model is us ed to predict the dissolution rate, the shape of the interface as well as the concentration field in austenite as a function of temperature. Both the transient and steady-state regimes are described. The model is first applied to a model alloy whose physical properties allow the problem to be solved for a wide range of lamellae spacings and tempera ture. Subsequently, the Fe-C system is examined and the numerical resu lts are compared with experimental data From the literature. Finally, it is shown that the steady-state growth breaks down and the transform ation occurs with a different regime at high superheating. (C) 1998 Ac ta Metallurgica Inc.