Modelling 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 structure of lamellar pearlite. The solution is obtained using a finite element method with a deforming mesh and a remeshing procedure. The main assumption of the model is the condition of local equilibrium at the interfaces, including the curvature contribution and mechanical equilibrium of surface tensions at the triple junction where the ferrite, austenite and cementite phases meet. The velocity of the interface is deduced from a solute balance which involves the concentration given by the phase diagram modified by the Gibbs-Thomson effect. The model is used 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 temperature. Subsequently, the Fe-C system is examined and the numerical results are compared with experimental data From the literature. Finally, it is shown that the steady-state growth breaks down and the transformation occurs with a different regime at high superheating. (C) 1998 Acta Metallurgica Inc.