Growth of Alloy Carbide Particles in Austenite

Abstract

The growth of Cr₇C₃, Mo₆C, VC and NbC carbides in austenite was examined in the ranges of temperature from 1173 to 1473 K, and time from 10 to 200 h. The growth rate decreases in the order Cr₇C₃, Mo₆C, VC and NbC. It was found that the carbides grew in two stages. The growth of carbides occurs initially by taking the solute from the matrix until an equilibrium is attained, and later by Ostwald ripening. For the carbides with lower growth rates, higher heating temperatures and/or longer times were required to reach the equilibrium. The rate equation in the stage of Ostwald ripening of alloy carbides in ternary Fe–C–M alloys was derived in the case in which the lattice diffusion of M atoms controlled the growth rate. The equation well described the growth rates of the alloy carbides in the latter stage.