Diffusion in Multicomponent Metallic Systems: Ii. Solutions for Two-Phase Systems With Applications to Transformations in Steel

The generalized differential diffusion equation for multicomponent systems with constant coefficients is solved for an advancing linear, cylindrical, or spherical two-phase interface. Representative numerical calculations for ternary alloys based on the iron, carbon system demonstrate how inhibition of the transformation austenite to ferrite + carbide can occur through the requirement of maintaining (extrapolated) equilibrium at the interface and through the interaction of carbon atoms with the off-diagonal gradients in the diffusion matrix. It is proposed that these interactions are the primary cause of hardenability effects in steel.