Refinement of Solidification Microstructure and Austenite Grain by Fine Inclusion Particles

The effect of deoxidation products of Ce2O3, ZrO2 and MgO particles on solidification microstructure has been studied in Fe–10mass%Ni, Fe–0.20mass%C–0.02mass%P and Fe–0.50mass%C–1mass%Mn alloys. The degree of the equiaxed crystallization is explained by the lattice misfit parameter between γ (or δ)-Fe and oxide. The single-phase solidification microstructure of Fe–10mass%Ni and Fe–0.50mass%C–1mass%Mn alloys is well related to austenite grain boundaries under the inhibition of grain growth by pinning. The correspondence between solidification structure and initial austenite grain has been studied in two-phases solidification of Fe–0.15 (or 0.30)mass%C–1mass%Mn–1mass%Ni alloy. The γ-grain size decreases with decreasing the lattice misfit parameter between γ-Fe and oxide and increases with decreasing the Zener pinning force. The number of γ-grains to that of primary δ-grains per unit area in a cross section increases with decreasing the aforementioned lattice misfit parameter, indicating that more than one nucleation event per δ-grain occurs at δ-ferrite grain boundary during δ to γ transformation.