等径角挤压变形奥氏体不锈钢的组织演变

 用实验方法研究了奥氏体不锈钢在等径角挤压冷变形(路径RC)过程中组织变化。实验结果表明：当剪切方向与孪晶带方向成一定角度时，在剪切力的作用下，孪晶逐渐由大块孪晶→由剪切带分割的孪晶(楼梯状)→小块状→奥氏体亚晶或马氏体晶粒；部分孪晶在剪切力作用下，剪切带可直接碎化成具有大角度位向差的细小晶粒(奥氏体亚晶+马氏体晶粒)，可发生马氏体相变；当剪切方向与孪晶带方向相同时，孪晶带区域也可发生马氏体转变；3道次变形后，具有明显特征的孪晶已很少，此后继续进行剪切变形，孪晶碎化组织(含马氏体)和奥氏体剪切滑移带(含碎化晶粒)的变形以剪切滑移方式进行，当奥氏体的滑移遇到阻力时，可局部形成局部形变孪晶来协调变形；随变形道次的增加，马氏体转变也越多，在多次剪切以及道次中的交叉滑移作用下，马氏体板条逐渐被高密度位错墙分割而碎化成细小的晶粒；8道次变形后，可获得60~230 nm的等轴晶粒。

Microstructure Evolution of Austenitic Stainless Steel During ECA Pressing

The microstructure evolution of austenitic stainless steel during equal channel angular pressing (ECAP) was studied experimentally . The results show that the big twins can be refined when the direction of shear band is different from that of twin lamella as follows: big block twin is divided into stairs by some shear bands →small block→austenitic subgrains or martensitic grain. Some of twin can be separated into fine grain with large angular grain boundary under large shear stress, and martensitic transformation occurs. When both shear band and twin lamella have the same direction , martensitic transformation can occur too within the twin. No obvious twins are observed after third pass of ECAP, both separated structure and austenitic shear band are deformed in the form of shear slip during continuous ECAP. Fine twin lamella is formed locally when austenitic grain is difficult to slip. Martensitic transformation increases with the increase of passes of ECAP. The bands of martensite are divided into finer grain gradually by dense dislocation wall after several shears and cross slip in one pass of ECAP. The equiaxed grains with 60-230 nm were obtained after the eighth ECAP.