| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1993: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1992: ¥1,400,000 (Direct Cost: ¥1,400,000)
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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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