V鋼の粒界初析フェライトの成長速度

抄録

Growth kinetics of intergranular ferrite in a V-N steel has been investigated from the measurement of isothermal transformation kinetics. When compared with a V-C steel, the start of intergranular ferrite transformation starts earlier on isothermal transformation in the V-N steel, whereas its growth is retarded. The growth rates of the intergranular ferrite are under the parabolic rate rule for both steels with a smaller rate constant for the V-N steel. When the rate constants are ascribed to the supersaturation of carbon at the ferrite/austenite interface, the carbon concentrations are estimated to be 0.29 and 0.35 mass% for the V-N and V-C steels, respectively. Johnson-Mehl-Avrami plot of the transformation kinetics indicates that the ferrite nucleation rate is larger for the V-N steel. It is discussed that the precipitation of intragranular ferrite in the V-N steel is facilitated owing to the retardation of the intergranular ferrite growth in the steel.