钢中贝氏体长大方式的TEM研究

利用ＴＥＭ考察了钢中贝氏体铁素体／奥氏体相界面台阶结构及奥氏体精细结构。用ＴＥＭ温台发现在贝氏体增厚过程中新形成的贝氏体中存在奥氏体预存孪晶；在贝氏体铁素体／奥氏体相界面存在台阶结构，但台阶阶面可对应于母相奥氏体中孪晶面或层错面，表明台阶的阶面为共格的滑移界面。因而贝氏体铁素体／奥氏体相界面可通过界面台阶沿面缺陷进行保守滑移，贝氏体长大具有滑移切变特征。根据实验结果提出了贝氏体二次层错切变模型及组织形貌示意图。

TEM Study of Growth Mechanism at the Initial Stage of Bainitic Reaction in Steels

The fine structures of residual austenite and the bainitic ferrite austenite interfacial structure are studied at the initial stage of bainitic reaction in Si containing steels by TEM double tilt and hot holder as well.The experimental results show that the retained austenite substructures may consist of twins,stacking faults and dislocations,the plastic accommodation effect of austenite occurs during bainitic growth.It is firstly observed by high temperature TEM that the freshly formed bainitic ferrite may inherit twin of parent austenite ,which strongly implies that the growth of bainitic ferrite is of shear nature.And,the ledge structures,usually larger than the atomic scale,exist at bainite/austenite interface.However,it is worth to note that the ledges usually correspond to twin or fault planes,which shows that the ledges are ordered and coherent to a high degree.Therefore,the bainitic ferrite/austenite interface can glide conservatively through the ledge slipping along the defect plane, ie ,the glide plane of austenite.The results give a strong prediction that the bainitic growth has the character of shear.