中锰钢两相区退火奥氏体逆转变的数值分析

根据中锰钢热轧组织结构确立两相区奥氏体化的几何模型和初始条件，利用DICTRA动力学分析软件对中锰钢马氏体基体奥氏体化过程进行计算分析。在奥氏体化初期的形核过程中，马氏体中过饱和的碳锰元素从铁素体迅速转移到奥氏体并在相界面奥氏体一侧聚集。后续的相变过程中，碳在奥氏体中快速均化，但锰在相界面奥氏体一侧的聚集加剧。相变初期奥氏体界面推移速度比中后期高出若干个数量级，但随时间推移迅速衰减。相变初期相界面推移是碳扩散主导，相变后期界面推移受到锰在奥氏体中扩散速度制约。温度升高可显著提高相界面推移速度。达到相同数量奥氏体的情况下，低温长时退火有利于锰从铁素体向奥氏体转移并提高其在奥氏体中的富集度，从而提高奥氏体的稳定性。

Numerical analysis on the austenite reverse transformation of medium manganese steel in intercritical annealing

According to the hot-rolled microstructure of medium manganese steel, a geometry model and initial conditions of inter-critical austenitization were established, and the DICTRA dynamic analysis software was used to calculate the austenitization on the martensitic matrix. It is found that supersaturated carbon and manganese in martensite quickly transfer from ferrite to austenite and aggregate at the austenitic side of the phase interface in the initial austenite nucleation stage. In the subsequent transformation, carbon rapidly homogenizes in austenite, but the aggregation degree of manganese in the austenitic side of the phase interface increases. The migration velocity of the austenite phase interface in the initial stage is several orders of magnitude higher than that in the middle and late stages, but rapidly decreases. The phase interface movement in the early transformation stage is dominated by carbon diffusion, but is restricted by manganese diffusion rate in austenite in the middle and late stages. Increasing the temperature can significantly improve the phase interface velocity. Under the condition of achieving the same amount of austenite, the low-temperature and longtime annealing is benefit for manganese transferring from ferrite to austenite and enriching in austenite, which will improve the stability of austenite.