利用Gleeble热力模拟、EBSD和TEM等方法，研究了Ni-30%Fe合金热变形后奥氏体的亚动态软化行为，分析了微观亚结构演化对奥氏体亚动态软化机制的影响。结果表明，亚结构恢复和亚动态再结晶是奥氏体亚动态软化的2种主要机制。当奥氏体内发生部分动态再结晶时，再结晶晶粒与变形基体间的储能差较大，热变形后保温过程的软化首先是通过亚动态再结晶进行；同时，变形基体内亚结构的恢复会逐渐降低变形基体内的形变储能，使晶界迁移速率降低而抑制亚动态再结晶的继续进行。而当奥氏体内动态再结晶发生完全时，在热变形后的保温过程中，再结晶晶粒内部因持续变形而形成的小角度亚结构会通过快速恢复而大量分解，形成不均匀的高密度位错会促进大角度晶界的局部迁移，从而促进晶粒的粗化，加速材料软化。

Multi-pass processing is commonly used in hot working of steels. Dynamic recrystallization (DRX) occurs during hot deformation, while post-dynamic softening takes place during the inter-pass times and post-deformation annealing. Three different mechanisms are believed to be responsible for the post-dynamic softening stage. These are static recovery (SRV), static recrystallization (SRX), and post-dynamic recrystallization (P-DRX). Each of these mechanisms can change the microstructure of austenite (i.e. grain size and distribution). As a result, the post-dynamic softening behavior of austenite may play an important role in the microstructures and the final mechanical properties of the steel product. In this work, a Ni-30%Fe model alloy is used to study softening of austenite in post-deformation annealing after the hot deformation at 900 °C and strain rate 0.001 s^-1. The microstructures in the annealed samples are carefully analyzed by EBSD in conjunction with TEM. The results show that P-DRX and sub-structural restoration are believed to be responsible for softening of the material after hot deformations. The P-DRX generally consumes deformed structures by the growth of the preformed nuclei of dynamic recrystallization. The sub-structural restoration in austenite usually takes place through the dislocation climb, leading to sub-boundary disintegrations and dislocation annihilations. When the sample is deformed to the peak strain, the deformation microstructure is composed of both recrystallized grains and deformed matrix. The large gradient of stored energy between the recrystallized grains and deformed matrix effectively promotes the strain-induced migration of the large-angle grain boundaries, which makes the P-DRX become the predominated post-dynamic softening mechanism during the post-deformation annealing. Meanwhile, the sub-boundaries within the deformed matrix gradually disintegrate through the restoration mechanism, which also contributes to the post-dynamic softening of austenite. On the other hand, the dislocation annihilation can result in a reduction of the stored energy within the deformation matrix, which inhibits the further migration of grain boundaries. In contrast, when the sample is deformed to the steady-state stage of the dynamic recrystallization, a fully recrystallized microstructure is obtained. The sub-structural restoration process of the fully recrystallized microstructure is much faster than that in the deformed matrix during the post-deformation annealing. It makes the sub-structural restoration become the predominated post-dynamic softening mechanism of this alloy in the steady-state condition. Furthermore, the disintegration of large numbers of sub-boundaries leads to an increase of the dislocation density in local region around the grain boundaries, which facilitates local migration of the high-angle grain boundaries and accelerates the softening of the material.