Influence of solute drag on bainite transformation in iron alloys

近两年来，我们研究了Fe-C-Mo和Fe-C-Ni合金中铁素体的相变行为和碳化物的析出，并对不完全相变的机理进行了探讨。在研究磁场对Fe-C-Mo合金中铁素体相变影响的过程中，发现磁场使铁素体相变向更短的时间和更高的温度方向移动。这归因于外加场导致转化驱动力增加，从而促进了海湾下方的转化动力学。本文认为，由于碳化物在Fe-C-Mo合金中的同时析出，在晶界以上促进铁素体相变的程度较小，并对文献中有关移动α/γ晶界局部条件的实验数据进行了评述。合金元素的扩散峰常被用来作为判别边界上准平衡和局部平衡条件的标准。发现即使在奥氏体中合金元素的峰宽小于奥氏体点阵参数的情况下，合金元素也会发生分配。这表明合金元素沿沿着α/γ晶界和铁素体内扩散明显。2004年12月在斯德哥尔摩举行的合金元素对奥氏体分解的影响研讨会上讨论了这些问题。

For the preceding two years ferrite transformation behaviors and carbide precipitation in Fe-C-Mo and Fe-C-Ni alloys were studied, and the mechanism for incomplete transformation was discussed. Also, a simulation model of diffusion-controlled growth of ferrite was developed incorporating solute drag due to alloying element accumulation at α/γ boundaries.In the study of the influence of magnetic field on the ferrite transformation in Fe-C-Mo alloys it was found that the bay was shifted to a shorter time and a higher temperature side by applying a magnetic field. This was attributed to the promotion of transformation kinetics below the bay because of the increase in the driving force of transformation due to the applied field. It is considered that the extent of the promotion of ferrite transformation is smaller above the bay because of the concurrent precipitation of carbides in the Fe-C-Mo alloy.Experimental data on the local condition at moving α/γ boundaries in literature were reviewed. The diffusion spike of an alloying element is often used as a criterion discriminating para-and orth-(or local) equilibrium condition at the boundary. It was found that alloying element partition occurred even in the situation in which the spike width of alloying element in austenite is less than the austenite lattice parameter. This indicates that the diffusion of alloying element significantly occurs along α/γ boundaries and in ferrite. These issues were discussed in the workshop on alloying element effects on austenite decomposition held in Stockholm in December, 2004.