Dynamics of phase transformations in steel obtained by controlled heating

本研究从(1)初始组织的影响、(2)合金元素的非平衡分配和(3)回复过程中的结晶约束三个方面研究了钢在回复过程中的组织变化。主要研究结果如下：高铁镍合金在奥氏体记忆回复过程中发生位移相变。然而，逆转变奥氏体位错密度过高会导致再结晶，从而导致记忆效应在进一步保温过程中消失。在Fe-Mn-C合金中，逆转变奥氏体有颗粒状和针状两种不同的形态。这些形态与马氏体基的结晶学特征是不同的。在回复过程中，粒状奥氏体相的形成是非平衡的，并在回复后期达到平衡。

In this study, microstructure change during reversion of steels was examined focussing on (1) effects of initial structure, (2) non-equilibrium partitioning of alloying elements, and (3) crystallographic constraints during reversion. Main results obtained are as follows.In Fe-high Ni alloys, displacive transformation occurs during reversion with austenite memory. However, a high dislocation density in reversely transformed austenite induces recrystallization which results in disappearance of the memory effect during further holding. In Fe-Mn-C alloys, reversely transformed austenite exhibits two kinds of distinctive morphologies, granular and acicular. Those morphologies are different in crystallographic character with respect to martensite matrix. Also, it was revealed that the granular austenite is formed in non-equilibrium in the beginning and reaches to the equilibrium in the later stage of reversion.