材料期刊网

外加应力使贝氏体相变形核率增大, 等温孕育期缩短, 即使所加应力远低于母相的屈服强度. 由于钢 中γ→α＋γ‘的形核驱动力较大(约为kJ/mol数量级), 贝氏体相变的膨胀应变能很小, 过小的外加应力对形核率的影响甚微. 考虑在外加应力的影响下, 会使界面能量有所下降, 也可能发生碳原子的再分布, 偏聚在晶界或其它缺陷, 甚至碳化物析出都会显著地增大形核率和缩短孕育期, 有待进一步实验给予证明. 无应力下, 贝氏体相变动力学可以用Avrami的等温相变方程来表述; 应力下则符合应力下铁素体及珠光体相变的动力学模型(经修改的Avrami方程). 形变奥氏体促发贝氏体相变, 但随后会发生奥氏体的力学稳定 化, 其机制可能和马氏体相变时的奥氏体力学稳定化不完全相同, 仅形变形成的位错阻碍贝氏体以一定位向长大, 使相变动力学迟缓. 贝氏体相变时奥氏体力学稳定化的模型有待建立.

Under the effect of stresses, the interphase energy may be reduced and probably the carbon atoms may redistribute, e.g., segregate at grain boundaries or other defects, and even the carbide may precipitate, resulting in the increase of the driving force for nucleation, in turn, marked raise of the nucleation rate and acceleration of incubation for bainitic transformation. The kinetics under stress is consistent with the kinetics model of ferrite and pearlite transformations under stress, i.e., the modified Avrami equation. Prior deformation of austenite may at first promote the bainite formation but may lead the occurrence of the mechanical stabilization of austenite at some later stage. The mechanism of the mechanical stabilization of austenite during bainite reaction may not be completely analogous with that during martensitic transformation, and it may only be the result from the hindrance of directional growth of bainite by dislocations formed in deformation, retarding the overall transformation kinetics. Model of the austenite mechanical stabilization is expected to be established.