贝氏体的长大是铁原子切变和碳原子扩散两个过程的耦合。贝氏体相变的驱动力来源于碳在相界上的类平衡,当773K时,Δμ_(Fe, Ch)~(γ→α)=800J/mol。低于400℃贝氏体铁素体实际长大所对应的相界扩散迁动阻力高于最大相变驱动力,故在此温度以下,铁素体不能扩散长大。而在550℃以下贝氏体以类平衡切变长大在热力学上是可能的。类平衡切变模型能在热力学上解释在400—550℃温区内两种长大机制的贝氏体的重迭;它又可说明贝氏体切变长大特征,而且还能定量的给出受碳扩散控制的长大动力学,并与多方面实验结果很好地相符。
The growth of bainitic ferrite is a couple process of the shear trans-formation of Fe atoms and the diffusion of C atoms. The diffusion growth of fer-rite is impossible when the temperature is below 400℃, and the paraequilibriumshear growth may occur at the temperature below 550℃. This paraequilibrium sheargrowth model explains the overlap of the bainites created from two growth mecha-nisms at 400--550℃.
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