Alloyed white iron graphitization

Abstract

1. The white iron graphitization process (graphite inclusions nucleation and growth) depends on the level of secondary phase carbon saturation at the graphite growth front. The thermodynamically unstable matrix region, in which the growth of in situ inclusions and the nucleation of fresh graphite inclusions may take place, varies with the rapid heating conditions and annealing at a fixed temperature. The graphitization mechanism that is typical of annealing at a fixed temperature (the in situ graphite inclusions develop as the cementite dissolves), is modified by rapid heating to high temperature to multiple graphite nucleation. 2. When white iron is alloyed with silicon, the level of the original matrix supersaturation with carbon is increased. Under rapid iron heating conditions to high temperatures where the carbon concentration gradient in the austenite is significant, silicon diffusion in the gradient field so alters the equilibrium carbon concentration in the austenite that multiple graphite inclusion nucleation becomes possible, although growth potential is limited.