2019 Volume 105 Issue 2 Pages 305-313
Effect of interphase boundary diffusion of carbon on pearlite transformation in Fe-C system is investigated by phase-field simulations. The model considers volume diffusion in α, γ and θ phases and boundary diffusion at α/γ and γ/θ interfaces. Growth velocity of pearlite at eutectoid composition is simulated under various conditions of interlamellar spacing at 873, 898 and 923 K. The simulation results show that growth velocity has a maximum value (ν) at an interlamellar spacing (λ) at each temperature. The simulated values of ν and λ at different temperatures satisfy the equation νλn=const.; the value of exponent n increases with increasing the value of boundary diffusion coefficient. This result suggests that the value of boundary diffusion coefficient can be estimated from phase-field simulations and experimental value of n. The ratio of volume diffusion flux to boundary diffusion flux (Rv/b) during the formation of pearlite is approximated from the values of volume diffusion coefficient in the γ phase, boundary diffusion coefficient and maximum growth velocity at each temperature. The value of Rv/b is small at 873 and 898 K while it is large at 932 K. It seems that the rate-controlling process of pearlite transformation changes from volume diffusion to interface diffusion with decreasing temperature at 873-932 K.