Microstructural Control by Dynamic Recrystallization and Phase Transformation

以无间隙钢（IF）和铁素体不锈钢为研究对象，研究了动态再结晶（DRX）和动态相变（DPT）对铁和钢晶粒细化的影响。主要研究结果总结如下：1和2的结果为中频钢，3和4的结果为中频钢1。DRX奥氏体表现为多步恢复过程，长时间退火后不会完全软化。中频钢中较细的DRX奥氏体晶粒导致较细的铁素体晶粒的演化。DRX奥氏体经过长时间退火后，铁素体晶粒几乎不长大。这是由于生长颗粒在DRX基体中稳定存在的结果。在奥氏体DRX晶粒中，细小的碳氮化物在高密度位错亚结构中析出。这可以导致奥氏体DRX晶粒的稳定，随后是细铁素体晶粒的演变。在亚稳奥氏体相中，铬铁素体钢的应力-应变曲线表现为应力峰值明显，工作软化迅速，在高应变下出现稳态流动。变形过程中的工作软化是由奥氏体（γ）向铁素体（α）相变引起的；也就是说，这被称为动态相变。然而，这种从γ到α的变换并不是静态地发生的。随着应变速率和温度的升高，动态相变产生的铁素体晶粒尺寸减小，导致室温硬度升高。

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.