Pressure Effect on the Diffusion of Carbon inα-Iron

Diffusion of carbon in $\alpha$-iron has been measured in the temperature range of 823 to 1000 °K and at pressures up to 6 kbar, using a radio-tracer diffusion couple technique. A large activation volume for the diffusion of carbon in $\alpha$-iron was obtained as compared to the zero activation volume found at room temperature by relaxation techniques. This volume is considerably larger than the activation volume Hilliard and Tully found for carbon diffusion in austenite but is nearly equal to the activation volume for austenite decomposition determined by Hilliard and Cahn and by Nilan.