The effect of deoxidation products of Ce 2 O 3 , ZrO 2 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 g (or d)-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 g-grain size decreases with decreasing the lattice misfit parameter between g-Fe and oxide and increases with decreasing the Zener pinning force. The number of g-grains to that of primary d-grains per unit area in a cross section increases with decreasing the aforementioned lattice misfit parameter, indicating that more than one nucleation event per d-grain occurs at d-ferrite grain boundary during d to g transformation.
The microstructure control through the refinement of solidification structure has been studied in an Fe-0.05ϳ0.30%C-1.0%Mn-1.0%Ni alloy as functions of particle characteristics of TiO X , Al 2 O 3 , ZrO 2 , Ce 2 O 3 and MgO and solidification mode. The numbers of d and g grains per unit area have been measured in the samples quenched at the start temperatures of g single phase (1 673 K at 0.05 % C, 1 743 K at 0.15 % C and 1 733 K at 0.30 % C). The nucleation event of g phase per one d grain per unit area increases with decreasing the lattice misfit parameter between oxide and g-Fe at 0.15 and 0.30 % C, not 0.05 % C. The results for g grain density whose inverse value corresponds to the g grain size can be explained by the grain-growth-inhibition effect. The g grain size decreases with increasing the Zener pinning force at 0.15 and 0.30 % C, not 0.05 % C. The g grain size obtained by quenching at the start temperatures of g single phase for 0.05 % C is considerably higher than that for 0.15 and 0.30 % C.KEY WORDS: deoxidation; solidification structure; lattice misfit parameter; austenite grain size; Zener pinning force; Fe-C alloy.kind of oxide phase. At non-steady state, however, the g grain size depends not only on the pinning force, but also strongly on carbon content. 5,6) It was found that the g grain size at the eutectic carbon content (0.17 % C) is highest, because the g grain growth is retarded in two phase regions by phase pinning.7)The refinement of microstructure in an Fe-0.15%C-1.0%Mn-1.0%Ni alloy using TiO X , MgO, ZrO 2 and Ce 2 O 3 particles has been previously studied.1) These results are discussed based on the lattice misfit parameter between oxide and d-Fe and that between oxide and g-Fe which correspond to the nucleation potency for the liquid/d and d/g transformations, respectively. Furthermore, the results for g grain size have been discussed based on the Zener pinning force.The purpose of this study is to clarify the effect of oxide phase and number of particles on the refinement of g phase through d phase control, based on the nucleation of g phase using the lattice misfit parameter between oxide and g-Fe and the g grain-growth-inhibition using the Zener pinning force. For this purpose, the effect of solidification mode on g grain size in an Fe-0.05ϳ0.30%C alloy deoxidized with Ti, Al, Zr, Ce or Mg has been systematically studied from the measurement of the numbers of d and g grains per unit area as a function of carbon content and oxide phase. It is to be noted that the d grain density is affected not only by the characteristics of oxide particles, but also by thermal gradient and solidification velocity, but in the present experiments the solidification structure was controlled under constant cooling rate. ExperimentalAn Fe-0.05, 0.15 or 0.30%C alloy (70 g) containing 1.0 % Mn and 1.0 % Ni was melted and deoxidized with an Fe-10%M (MϭTi, Al, Zr or Ce) or Ni-10%Mg alloy at 1 873 K in an alumina crucible using an induction furnace (100 kHz) (% and ppm represent mass% and mass ppm, respectiv...
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