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| THERMODYNAMICS(KRC MODEL)OF THE BAINITIC TRANSFORMATION IN Fe-C ALLOYS |
| XU Zuyao(T.Y.Hsu);MOU Yiwen Shanghai Jiaotong University |
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Cite this article:
XU Zuyao(T.Y.Hsu);MOU Yiwen Shanghai Jiaotong University. THERMODYNAMICS(KRC MODEL)OF THE BAINITIC TRANSFORMATION IN Fe-C ALLOYS. Acta Metall Sin, 1985, 21(2): 13-24.
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Abstract By application of the improved KRC model for determination of △G~(γ→α),the total driving forces for transformation and driving forces for growth(nucle-ation)for the several possible mechanisms of the bainitic transformation in Fe-Calloys,i.e.,γ→α+γ_1,γ→α+Fe_3C and γ→α′(the same composition)and α′→Fe_3C+α_B(the composition of the bainitic ferrite)are calculated.The driving forceof γ→α+Fe_3C is the largest,followed by that of γ→α+γ_1 and that of γ→α′isthe smallest.The driving force for growth of γ→α′is far less than that of γ→α+γ_1.At the temperature range of bainite formation,the driving force for γ→α′ismuch lower than that required for shear mechanism.The driving force for trans-formation of γ→α+γ_1 in 0.1—0.55 wt-%C alloys at B_s temperature is onlyabout -45 J·mol~(-1).At the upper limit temperature of bainite formation,the driv-ing force of γ→α′in 0.8 wt-%C alloy-is about 137 J·mol~(-1),and that of α′→α_B+Fe_3C is—527 J·mol~(-1).If cementite precipitates from the bainitic ferrite,thetotal driving force,i.e.,the sum of the driving forces of the above two processesis only about -390 J·mol~(-1).The above results show that the formation of thebainitie ferrite by shear mechanism is thermodynamically impossible.
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Received: 18 February 1985
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