IN SITU OBSERVATION OF GROWTH BEHAVIOR AND MORPHOLOGY OF DELTA-FERRITE AS FUNCTION OF SOLIDIFICATION RATE IN AN AISI304 STAINLESS STEEL
来源期刊：Acta Metallurgica Sinica2006年第6期
论文作者：G.F. Liang G.M. Zhu Y. Fang J.C. Wu C.Q. Wan Y. Yu
Key words：stainless steel; confocal scanning laser microscopy; δ-ferrite; in situ observation; solidification;
Abstract: 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→δtransformation 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.
G.F. Liang1，G.M. Zhu1，Y. Fang1，J.C. Wu1，C.Q. Wan1，Y. Yu1
(1.Advanced Technology Institute, Technology Center of Baosteel, Shanghai 201900,China;
2.Department of Materials Science and Engineering, Shanghai Jiao Tong University,Shanghai 200030, China)
Abstract: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→δtransformation 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.
Key words:stainless steel; confocal scanning laser microscopy; δ-ferrite; in situ observation; solidification;
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