Application of commercial computer codes to modeling the carburizing kinetics of alloy steels

Abstract

When steels remain single phase during carburizing, it is well known how to model their carburizing kinetics with finite difference and finite element computer codes . [1-41 In addition to writing original computer codes, investigators can apply commercial codes for heat-transfer analysis by making the following substitutions: tSl carbon concentration for temperature, diffusivity of carbon for thermal conductivity, and the integer one for the product of density and specific heat. In this case, the only property data needed are the carbon diffusivity vs carbon concentration and information about the boundary conditions (e.g. , constant concentration at the surface). When alloy steels form carbides in the carburized zone, for example, as occurs in M50NiL, t61 the same computer codes can be applied except that additional physical property data are needed. The following work describes the data that are needed, indicates how the data are entered in heat-transfer programs, and suggests a method for obtaining the data from a single carburizing experiment. The basis for modeling multicomponent, multiphase carburizing is the following mass balance equation which states that the total carbon (carbide plus matrix carbon) in a differential volume element, ct~ ~ changes with time, t, according to the divergence of the carbon flux: