Growth kinetics of grain boundary allotriomorphs of proeutectoid ferrite in Fe-C-Mn-X{sub 2} alloys
- Carnegie Mellon Univ., Pittsburgh, PA (United States)
- Ibaraki Univ. (Japan). Dept. of Materials Science
The parabolic rate constant for the thickening of grain boundary ferrite allotriomorphs at the faces of austenite grain boundaries was measured as a function of isothermal transformation temperature in three Fe-C-X{sub 1}-X{sub 2} alloys where X{sub 1} is Mn and X{sub 2} is successively Si, Ni, and Co. The results were compared with the predictions of the local equilibrium model for multi-component systems and with those derived from the theory of growth under paraequilibrium conditions. The distribution of Mn and Si in ferrite and austenite in the Fe-C-Mn-Si alloy was also measured as a function of reaction temperature with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The observed temperature below which alloying element partition ceased was in good agreement with the local equilibrium model. Whereas the parabolic rate constant for thickening was considerably larger than the amount predicted by this theory in the alloying element diffusion-controlled regime, the opposite was true in the carbon diffusion-controlled regime. Similarly, the calculated paraequilibrium constant was usually considerably larger than that measured experimentally. Synergistic enhancements of the effects of Mn and X{sub 2} in diminishing thickening kinetics were observed for each X{sub 2}. The time-temperature-transformation (TTT) curves for the beginning of transformation were calculated from a modified Cahn analysis for the overall kinetics of grain-boundary-nucleated reactions using values of the nucleation rate and the parabolic growth rate constant computed from various models and compared with experimentally determined TTT curves.
- OSTI ID:
- 31963
- Journal Information:
- Metallurgical Transactions, A, Vol. 26, Issue 3; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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