微合金钢初始凝固中奥氏体开始长大的温度

通过共聚焦激光显微镜对P510L钢的初始凝固过程进行了原位动态观察以考察δ相生成、包晶反应以及γ相的形成过程，并探索奥氏体开始长大温度.研究结果表明:1)冷却速度为25℃/s时P510L钢的冷却模式为首先从液相中析出δ铁素体，然后在液相与δ铁素体相之间发生包晶反应(L+δ→γ)，进入三相共存区，液相消失后剩余的δ相通过固态扩散转变为γ相；2)在初始凝固过程中，奥氏体先进行一部分吞并、长大，然后才实现过剩δ铁素体向奥氏体的同素异构转变，最后实现完全奥氏体化；3)通过原位动态观察，探索了一种较为准确的确定原始奥氏体开始长大温度的实验方法，提高了奥氏体晶粒预测模型的准确性.

Investigations on the Temperature for Completion of Austenite Transformation During the Initial Solidification Process of Micro alloy Steels

Coarse austenite grain formed in the initial solidification process is an important factor to affect the transverse cracking of medium carbon micro alloyed steels.The initial solidification process of P510L steels were observed by the confocal laser scanning microscope in order to inspect the formation of δ and γ phases and the peritectic reaction，and explore the temperature for the completion of γ transformation. The results showed that:1) With the cooling rate of 25℃/s， the cooling mode of P510L steel was that δ ferrite precipitated from the liquid phase first， then the peritectic reaction (L+δ→γ)occured between the δ ferrite phase and the liquid phase， then they entered to the three phase coexistence region. With the liquid phase disappeared， the remain δ phase transformed into γ phase by the solid state diffusion;2) In the initial solidification process， parts of the austenite grains annexed and grew up first， then the remain δ ferrite transformed into austenite with the allotropic heterogeneous， and the fully austenite region achieved at last; 3) A more accurate method about determining the temperature for the completion of γ transformation was sought by in situ dynamic observation， and the accuracy of a model for predicting the austenite grain size was thus improved.