Microstructural Control by Dynamic Recrystallization and Phase Transformation

采用无间隙原子（IF）钢和铁素体不锈钢研究了动态再结晶（DRX）和动态相变（DPT）对钢铁晶粒细化的影响。主要研究结果如下。1和2的结果是IF钢，3和4的结果是后者。动态再结晶奥氏体表现出多步回复过程，并且在长时间退火后不会完全软化。IF钢中的动态再结晶奥氏体晶粒细化导致铁素体晶粒细化。动态再结晶奥氏体经长时间退火后，铁素体晶粒几乎不长大。这是由于动态再结晶基体中生长晶粒的稳定存在.在奥氏体动态再结晶晶粒中发展的高密度位错亚结构上析出细小的碳氮化物。这可能导致奥氏体动态再结晶晶粒的稳定化，随后在快速冷却过程中演变为细小的铁素体晶粒。在亚稳奥氏体相中，铬铁素体钢的应力-应变曲线显示出尖锐的应力峰和快速的加工软化，然后在高应变下出现稳态流变。加工软化是由变形过程中奥氏体（γ）向铁素体（α）相变引起的;即，这被称为动态相变。然而，这种gamma到alpha的转换并不是静态发生的。4.随着应变速率和温度的升高，动态相变引起的铁素体晶粒尺寸减小，导致室温硬度增加。

The effects of dynamic recrystallization (DRX) and dynamic phase transformation (DPT) on the grain refinement of iron and steels were studied by using interstitial free (IF) steels and a ferritic stainless steel. The main results are summarized as follows. The result of 1 and 2 are for IF steels, and those of 3 and 4 for the latter steel.1. The DRX austenite shows multiple-step restoration processes and do not go to full softening for a long period of annealing time. Finer DRX austenite grains in IF steels lead to the evolution of finer ferrite grains compared with usual grains. Ferrite grains scarcely grow even after annealing of DRX austenite for a long period of time. These results from the stable existence of growing grains in DRX matrices.2. Fine carbonenitrides precipitate on high density dislocation substructures developed in austenitic DRX grains. This can result in the stabilization of austenitic DRX grains, followed by the evolution of fine ferrite grains during repid cooling.3. Stress-strain curves of a crominum ferritic steel in the metastable austenite phase show a sharp stress peak and a rapid work softening, followed by a steady state flow at hihg strains. The work softening results from austenite (gamma) to ferrite (alpha) phase transformation during deformation ; namely, this is termed dynamic phase transformation. This kind of gamma to alpha transformation, however, does not statically take place.4. Ferritic grain sizes evolved by dynamic phase transformation decrease with increasing strain rate and temperature, leading to increase in room temperature hardness.