Analysis of the γ→α transformation in a C-Mn steel by phase-field modeling

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2005-09, Vol.36 (9), p.2327-2340
• Main Authors: MECOZZI, M. G, SIETSMA, J, VAN DER ZWAAG, S, APEL, M, SCHAFFNIT, P, STEINBACH, I
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Metals. Metallurgy
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-005-0105-4

This article deals with the austenite (gamma) decomposition to ferrite (alpha) during cooling of a 0.10 wt pct C-0.49 wt pct Mn steel. A phase-field model is used to simulate this transformation. The model provides qualitative information on the microstructure that develops on cooling and quantitative data on both the ferrite fraction formed and the carbon concentration profile in the remaining austenite. The initial austenitic microstructure and the ferrite nucleation data, derived by metallographic examination and dilatometry, are set as input data of the model. The interface mobility is used as a fitting parameter to optimize the agreement between the simulated and experimental ferrite-fraction curve derived by dilatometry. A good agreement between the simulated alpha-gamma microstructure and the actual alpha-pearlite microstructure observed after cooling is obtained. The derived carbon distribution in austenite during transformation provides comprehension of the nature of the transformation with respect to the interface-controlled or diffusion-controlled mode. It is found that, at the initial stage, the transformation is predominantly interface-controlled, but, gradually, a shift toward diffusion control takes place to a degree that depends on cooling rate.