1993 Fiscal Year Final Research Report Summary
Thermodynamic Study on Microstructure Control in Microalloyed Steels
| Project/Area Number |
04650641
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
金属材料(含表面処理・腐食防食)
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| Research Institution | Tohoku University |
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Principal Investigator |
OHTANI Hiroshi Tohoku Univ. Fac. Eng. Research Associate, 工学部, 助手 (70176923)
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| Co-Investigator(Kenkyū-buntansha) |
ISSHIDA Kiyohito Tohoku Univ. Fac. Eng. Professor, 工学部, 教授 (20151368)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Microalloyed steels / Phase diagrams / Phase equilibria / Austenite / Microstructure / IF steels / Carbonitrides / Aloy design |
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| Research Abstract |
The purpose of the present research is to analyze the phase equilibria of the carbonitrides in microalloyed steels and to develop a method to calculate the complicated phase relationship.
1. Miscibility gaps in some transition-metal carbide or carbonitride systems have been experimentally studied. The systems investigated were (V,Nb)(C,N), (Ti, Nb)(c, N) and (Ti, V)(C,N), and the equilibrium compositions were determined by the X-ray measurements and EDX analysis. A thermodynamic calculation of the miscibility gaps was performed on the basis of the experimental results. The Gibbs energy of the carbonitrides has been described using a sublattice model and the interaction energies in the pseudobinary systems were estimated from the difference in lattice constants in components. The miscibility gaps in the 10(X,Y)(C,N) types of carbonitrides were calculted.
2. A thermodynamic model was developed to calculate the composition of austenite as well as that of complex carbonitrides in the microalloyed steels containing Ti, V and Nb. The thermodynamic model was applied to the phase equilibrium calculation between the austenite and carbonitrides. Some variation of precipitation mode was observed through the calculation accoding to the alloy contents and kinds of additional elements. The effect of individual element was briefly summarized as follows : (a) Ti additon to the microalloyed steels enhances the formation of Ti-rich nitrides mainlydue to its extreme low solubility in austenite. (b) Complex addition of the elements brings the phase separation of the carbonitrides, and in almost cases the separation between NbC, VC and NbC, and TiN is presented. These phenomena can be explained from the view points of the relative stability of binary compounds.
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