钢中珠光体相变机制的研究进展

简要总结了钢中珠光体相变的机制，特别是珠光体形核的晶体学和长大的动力学。基于形核时的最小形核能和渗碳体与铁素体“合作”生长的要求，珠光体通常在奥氏体晶界形核并只向某一晶粒内生长，因而晶界珠光体与相邻晶粒存在特定取向关系而与生长进入的晶粒无特定取向关系。晶体学研究表明，珠光体形核的领先相与碳浓度及渗碳体与铁素体间的取向关系(分别为Pitsch-Petch、Bagaryatsky或lsaichev)无关。最近的研究发现，具Bl结构的非共格杂质粒子界面是过共析钢中晶内珠光体形核的有效位置，初步的结果表明，晶内珠光体形核的原因在于杂质粒子生长造成的局部区域碳贫化及低能的珠光体，杂质界面取代高能的奥氏体，杂质界面。特定过冷度下的层片间距与正向界面推移速率的关系是珠光体生长动力学的主要问题。基于珠光体与奥氏体间的无序界面假设和稳态扩散方程分别发展了以体扩散控制和以界面扩散控制为主的动力学理论。两种理论均与实验结果符合较好，但后者似更合理。最近的实验在珠光体中发现了生长台阶与结构台阶，表明生长动力学方程需要修正。

Progress in the Pearlitic Transformation Mechanism in Steels

The mechanisms for the formation of pearlite in steels are reviewed in brief with particular reference to the role of crystallography in nucleation and the kinetics of growth. Due to the requirements of both minimum barrier during nucleation and cooperative process of ferrite and cementite during growth, the pearlite usually nucleates at grain boundary of austenite but only grows into one of grains, which results in the fact that pearlite can has specific orientation relationship (OR) with respect to the austenite grain into which it does not grow while it has no reproducible OR with respect to the austenite grain into which it grows. The crystallographic investigation shows that the active nucleus for pearlite nucleation has no relationship with both the concentration of carbon in austenite and the possible OR between ferrite and cementite (Pitsch-Petch, Bagaryatsky or Isaichev). The recent result indicates that the interface between austenite and incoherent inclusions with B1 structure can act as the effective nucleation site for intragranular transformation in hypereutectoid steel. The effect of inclusion may attribute to both the depletion of carbon at local area due to the growth of inclusion and the replacement of high energy interface between inclusion and austenite by low energy interface between inclusion and pearlite. The relationship between the lamellar spacing and the edgewise growth velocity under the specific undercooling is the core of growth kinetics. Both the theoretical models for volume diffusion control and boundary diffusion control are well developed under the assumption of the disorder interface between pearlite and austenite and based on the steady-state diffusion equation. It is concluded that both models are reasonably compared with experimental results although the latter seems to be more preferable. The observation of structural ledges associated with the movement of growth ledges at interface between pearlite and austenite suggested that the kinetic equation should be modified further.