904L不锈钢形变奥氏体的亚结构演化及其对宏观流变应力的影响

为了揭示动态再结晶行为的本质及其对流变应力的影响，选取904L奥氏体不锈钢为研究对象，针对奥氏体在不同工艺下的热变形行为以及变形组织和再结晶组织的亚结构进行深入研究。结果表明材料的宏观应力-应变曲线在特定条件下不能准确反映微观尺寸上的动态再结晶行为。EBSD分析表明动态再结晶晶粒中亚结构特征以取向差角小于1°为主，呈周期性分布，且这种特征不会随晶粒自身长大或应变的增加而发生明显改变，即具有较好的稳定性；而变形组织中亚结构的取向差角明显增大，频繁出现大于1°的小角晶界，局部取向差角的分布范围也增大至1°～4°，即几何必需位错密度显著增加。尽管无论何种工艺下晶界均为再结晶的优先形核位置，但形核条件是不同的。对于完全再结晶组织来说，新的再结晶晶粒形核只需晶界出现局部“弓出”或弯曲；而在原始变形组织中，出现再结晶形核的晶界均存在微区高应变。

Substructure Evolution in Deformed Austenite of 904L Stainless Steel and Its Effect on Macro Flow Stress

To explore the nature of dynamic recrystallization behavior and its effect on flow stress, in this work, a 904L super austenitic stainless steel was employed to study the hot deformation behavior with different deformation processes and the evolution of substructures in deformed matrix and recrystallized grains. The results showed that under a certain conditions the stress- strain curve obtained during hot processing cannot reflect the dynamic recrystallization events at the microscopic scale. Based on EBSD analysis, the substructure of recrystallized grains is characterized by the misorientation angle lower than 1° and they are distributed periodically. This feature is relatively stable and does not change with the grain growth as well as straining. In contrast, the misorientation angle of substructure in deformed matrix increases obviously with straining, where the low angle boundaries with misorientation higher than 1° frequently occurs. The main distribution range of local misorientation is enlarged from 1° to 4°, which means that the geometrically necessary dislocations are notably increased in the deformed matrix. Although under any processing condition the grain boundary acts as a preferable place to nucleate a new recrystallized grain, their nucleation conditions are quite different. For totally recrystallized microstructure, a portion of grain boundary bulging is enough to promote the nucleation; while in deformed matrix, the high micro-strain is a necessity for the grain boundary assisted nucleation.