It was presented the in situ observation of growth behavior and morphology of delta-ferrite as a function of solidification rate in an AISI304 stainless steel. The specimens have been solidified and observed using con...It was presented the in situ observation of growth behavior and morphology of delta-ferrite as a function of solidification rate in an AISI304 stainless steel. The specimens have been solidified and observed using confocal scanning laser microscopy (CSLM). The δ-phase always appears like cells on the sample surface when critical supercooling occurs, during which the L→δ transformation starts. The solid-liquid (S-L) interface is found to be finger shaped and has no faceted shape. γ phase appears among δ grains due to partitioning of Ni into the melt during solidification, when solidification rate is higher. The mergence of observed δ cells is possible for the steel sample cooled at 7.5℃/min. The formation of dendrites can be observed on the free surface of the steel sample cooled at 150℃/min. The size of solidified delta grains decreases from 120 to 20-80μm, and the volume fraction of solidified austenite increases with increase in solidification rate from 7.5 to 150℃/min. The relation between the tip radius of δ cell and its growth rate is deduced, and the results agree with the experimental values.展开更多
Results presented in this paper contribute to investigation of the granulation mechanisms of γ+(Fe,Mn)3C eutectics in the austenite matrix composites (abbreviated EAMC). The specimens corresponding to the nominal com...Results presented in this paper contribute to investigation of the granulation mechanisms of γ+(Fe,Mn)3C eutectics in the austenite matrix composites (abbreviated EAMC). The specimens corresponding to the nominal composition of eutectic with controlled RE(Ce)-Mg agent modifier additions have been unidirectional solidified with a constant growth rate of 2.18μm/s at a fixed temperature gradient of 800K/cm using vertical Bridgeman method. With the RE-Mg agent modifier, the transition of solid/liquid (S/L) interface from columnar to dendrite (CDT), refinement and developed branching of γ and (Fe,Mn)3C phases in the eutectics, and the transition of growth style from faceted-nonfaceted (F/NF) to nonfaceted-nonfaceted (NF/NF) for γ and (Fe,Mn)3C phases in the eutectic have been observed and investigated theoretically. Those can explain the granulation of γ+(Fe,Mn)3C eutectics in the as cast because the roundness increases with the developed lateral branching of primary austenite dendrites, refinement of eutectics, and NF/NF growth of γ and (Fe,Mn)3C phases in the eutectic.展开更多
Results presented in this paper contribute to investigation of the effect of the added Ca-Si modifier amount ( ) on the microstructure scales of granular γ-(Fe,Mn)3C eutectics such as the volume fraction (f) and di...Results presented in this paper contribute to investigation of the effect of the added Ca-Si modifier amount ( ) on the microstructure scales of granular γ-(Fe,Mn)3C eutectics such as the volume fraction (f) and diameter (d) in the austenite steel matrix composites (EAMC). Directional solidification of EAMC has been carried out using vertical Bridgman method at 50.6μms-1 with a constant temperature gradient about 800Kcm-1. The higher constitutional supercooling ahead of solid-liquid interface attributing to the larger results in the enlargement of γ-(Fe,Mn)3C coupled-zone and the increment of the nucleation rate of eutectics. Therefore, f increases with increasing . The branches of the primary austenite dendrites develop more greatly as increases, which limits the growth of eutectics. As a result, d decreases with increasing .展开更多
基金This work was supported by the China Postdoctoral Science Foundation (No. 20060390150).
文摘It was presented the in situ observation of growth behavior and morphology of delta-ferrite as a function of solidification rate in an AISI304 stainless steel. The specimens have been solidified and observed using confocal scanning laser microscopy (CSLM). The δ-phase always appears like cells on the sample surface when critical supercooling occurs, during which the L→δ transformation starts. The solid-liquid (S-L) interface is found to be finger shaped and has no faceted shape. γ phase appears among δ grains due to partitioning of Ni into the melt during solidification, when solidification rate is higher. The mergence of observed δ cells is possible for the steel sample cooled at 7.5℃/min. The formation of dendrites can be observed on the free surface of the steel sample cooled at 150℃/min. The size of solidified delta grains decreases from 120 to 20-80μm, and the volume fraction of solidified austenite increases with increase in solidification rate from 7.5 to 150℃/min. The relation between the tip radius of δ cell and its growth rate is deduced, and the results agree with the experimental values.
基金supported by the National Natural Science Foundation of China(No.50001008).
文摘Results presented in this paper contribute to investigation of the granulation mechanisms of γ+(Fe,Mn)3C eutectics in the austenite matrix composites (abbreviated EAMC). The specimens corresponding to the nominal composition of eutectic with controlled RE(Ce)-Mg agent modifier additions have been unidirectional solidified with a constant growth rate of 2.18μm/s at a fixed temperature gradient of 800K/cm using vertical Bridgeman method. With the RE-Mg agent modifier, the transition of solid/liquid (S/L) interface from columnar to dendrite (CDT), refinement and developed branching of γ and (Fe,Mn)3C phases in the eutectics, and the transition of growth style from faceted-nonfaceted (F/NF) to nonfaceted-nonfaceted (NF/NF) for γ and (Fe,Mn)3C phases in the eutectic have been observed and investigated theoretically. Those can explain the granulation of γ+(Fe,Mn)3C eutectics in the as cast because the roundness increases with the developed lateral branching of primary austenite dendrites, refinement of eutectics, and NF/NF growth of γ and (Fe,Mn)3C phases in the eutectic.
基金supported by the National Natural Science Foundations of China(Grant No.50001008 and No.50271042).
文摘Results presented in this paper contribute to investigation of the effect of the added Ca-Si modifier amount ( ) on the microstructure scales of granular γ-(Fe,Mn)3C eutectics such as the volume fraction (f) and diameter (d) in the austenite steel matrix composites (EAMC). Directional solidification of EAMC has been carried out using vertical Bridgman method at 50.6μms-1 with a constant temperature gradient about 800Kcm-1. The higher constitutional supercooling ahead of solid-liquid interface attributing to the larger results in the enlargement of γ-(Fe,Mn)3C coupled-zone and the increment of the nucleation rate of eutectics. Therefore, f increases with increasing . The branches of the primary austenite dendrites develop more greatly as increases, which limits the growth of eutectics. As a result, d decreases with increasing .
