THEORY FOR REAUSTENITIZATION FROM FERRITE CEMENTITE MIXTURES IN FE-C-X STEELS/

Phase transformation theory for the formation of austenite from substi tutionally alloyed ferrite/cementite mixtures is discussed. The local equilibrium assumption is adopted. Diffusion of carbon in ferrite and cementite is ignored, together with the ternary diffusional interactio ns. The ferrite and cementite phases are assumed to be semi-infinite i n extent, so that soft impingement effects are not accounted for. Subj ect to these assumptions, exact solutions are presented for one-dimens ional (planar) growth. The solution method involves the determination of the appropriate tie-lines at the cementite/austenite and austenite/ ferrite interfaces. Potential numerical difficulties which arise in de termining the solution are discussed. It is found that for reasonable values of the diffusion coefficients involved, the governing equations can be simplified. The results are presented in the form of reverse t ime-temperature-transformation diagrams, and comparisons with recent r esults for reaustenitisation from binary Fe-C steels are made. The eff ects of silicon and manganese as ternary alloying additions are quanti fied.