Simulation of B Segregation at Austenite Grain Boundary in Low Carbon Steel

Abstract

The diffusion and segregation of boron (B) at the austenite grain boundary have been simulated in continuously cooled low carbon steels to elucidate the role of vacancy, the influence of austenite grain size and thermodynamic interaction between solutes. First-principles calculations were carried out to obtain the stable configuration of B-vacancy complexes and the binding energies therein. The thermodynamic equations of a hybrid interstitial-substitutional solid solution were utilized to evaluate the contribution of interstitial B atoms and B-vacancy complexes to boundary enrichment. The latter contribution did not appear to be significant probably due to their small concentration and/or low mobility. The grain growth of austenite is likely to play a significant role in B enrichment at elevated temperatures. Due to the strong C-Mo interaction, the carbon flux in the grain interior did decrease, but the interaction within the grain boundary had a much greater influence on the segregation amount. The B enrichment in an Fe-C-B-Mo quaternary alloy was simulated for comparison with experiment. A sophisticated approach, e.g., segregation energies spectrum, may be necessary to reproduce adequately the B segregation behavior, which also depends sensitively on process parameters and microstructure.