COARSENING RESISTANCE OF M2C CARBIDES IN SECONDARY HARDENING STEELS .1. THEORETICAL-MODEL FOR MULTICOMPONENT COARSENING KINETICS

Abstract

The development of very high-strength levels in many alloy steels is achieved by a secondary hardening reaction. In high Co-Ni steels containing the strong carbide-forming elements Mo, Cr, and W, secondary hardening is accomplished by the precipitation of fine-scale M2C alloy carbides. Coarsening resistance of the M2C precipitates depends on the alloy content of these elements, and there should be an addition to the alloy of these carbide-forming elements which optimizes the M2C coarsening resistance. Current Lifshitz-Slyozov-Wagner (LSW) theory[2,3] cannot properly be used to describe the coarsening behavior of multicomponent carbides, which involves concentrations and diffusivities of two or more solutes and nonspherical carbide morphologies. A model is introduced for the coarsening resistance of multicomponent carbides. This model treats the coarsening of shape-preserving particle and is applicable to rodlike particles.