Theoretical Analysis of Grain Boundary Carbide Precipitation in Stainless Steels

Abstract

It has been well-known that grain boundary carbide precipitation in ferritic stainless steels is faster than that in austenitic ones. However, there were few theoretical studies for this problem compared with that of austenitic ones. The aim of this study is to formulate the thermodynamic data such as activities of Cr and as the formation energies of carbides from many references and to compose a carbide precipitation model based on local equilibrium and diffusion control.
Amounts and compositions of precipitated carbides and Cr contents near grain boundaries were calculated from model and were in good agreement with the experimental data. TTS (Time-Temperature-Sensitization) diagrams were evaluated by calculating Cr content near the grain boundaries and the amounts of total precipitates. The sensitization of a 0.01%C ferritic stainless steel became 10⁵ times as rapid as that of a 0.03%C austenitic ones.