1996 Fiscal Year Final Research Report Summary
Influence of Alloying Element Segregation on the Growth of Ferrite/Austenite Interfaces
| Project/Area Number |
07650756
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | Ibaraki University |
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Principal Investigator |
ENOMOTO Masato Ibaraki University, Department of Materials Science, Professor, 工学部・物質工学科, 教授 (70241742)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Iron alloy / Ferrite transformation / TTT-curve / Interfacial segregation / Local equilibrium / Paraequilibrium |
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| Research Abstract |
An Fe-0.3mass% C-3mass% Mo alloy was vacuum-melted and was homogenized at 1250ﾟC for 50 h. The specimens were then austenitized and reacted isothermally at temperatures ranging from 400 to 700ﾟC.The fraction transformed was measured in each specimen and TTT curves for the initiation of transforma-tion, determined.
The transformation kinetics were fast below 530ﾟC,where "degenerate ferrite" was formed. The kinetics were slow between 550 and 570ﾟC and increased rapidly with increasing temperature. The bay temperature was deter-mined to be -560ﾟC.
Under transmission electron microscope the degenerate ferrite was observed to be the aggregate of equiaxd fine grains of ferite. These grains were consider ed to be a section of one large ferrite crystal, whose shape resembled a tree or a coral. It was also considered that these crystals were formed as a result of strong inhibition of growth in some crystallographic directions.
The segregation of alloying elements to ferrite/austenite interfaces may be one reason for the retardation of growth. The chemical composition of interfaces was analyzed by FE-TEM.The Mo concentration was observed to be more than 2 times the average concentration in the alloy at many interfaces. The Mo concentration tended to increase with the isothermal holding time.
A part of driving force for transformation may be dissipated by diffusion of segregants in the interfacial region. Coupled with strong interaction of Mo with carbon this may cause the retardation of ferrite growth and account for the irregular transformation behavior in this alloy system.
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Research Products
(2 results)
