Comparison between the Capability of MgO and that of TiN on the Heterogeneous Nucleation of δ-Fe Containing 0.05 mass%C

Abstract

A tablet made of one of either TiN, MgO or α-Al₂O₃ was immersed in molten steel containing 0.05 mass%C and undercooling for nucleation of δ-Fe was measured. Undercooling was smaller in order of TiN, MgO, α-Al₂O₃. Namely undercooling in case of a TiN tablet immersion was the smallest, no more than 2.1 K. This result shows that although disregistry between δ-Fe and MgO is nearly equal to that between δ-Fe and TiN, MgO is obviously less effective heterogeneous nucleation site for δ-Fe than TiN. Chemical term and structural term which were parts of interfacial energies acting for nucleation of δ-Fe were calculated. It is concluded that because chemical term, (γ_CL^ch–γ_CS^ch)/γ_SL, in case of MgO is much smaller than that in case of TiN, MgO is less effective than TiN.