Abstract

Phase change of steel during cooling affects the slab qualities in continuous casting. Especially, crack susceptibility of hypo peritectic steel is high because large volume shrinkage occurs by peritectic phase transformation during solidification and cooling. In continuous cooling, phase change is different from the behaviors under the equilibrium condition, such as undercooling and extend of peritectic reaction, etc. Therefore, we develop a new phase change model considering thermodynamics, empirical equations, and carbon diffusion in each phase to predict phase change behavior during continuous cooling. In this model, phase change of hypo peritectic steel comprises 5 stages until all phases become the γ phase. The velocities of the δ/γ interface and phase fractions during cooling are calculated according to cooling rate, undercooling of the γ phase, and carbon contents. The results show that if solidification ends by the δ phase during dT_p, the γ phase is formed by massive transformation. On the contrary, if peritectic reaction starts with liquid, the γ phase is formed and grows by diffusional transformation. In latter case, massive transformation of remaining δ phase can occur with high undercooling or very fast cooling rates. This analysis shows that there are several different paths depending on carbon contents of hypo peritectic steels.

Graphic Abstract

Phase change of hypo peritectic steel.

中文翻译：

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连续冷却的低晶包晶钢的相变建模

摘要

冷却过程中钢的相变会影响连铸的板坯质量。特别是，由于在凝固和冷却过程中由于包晶相变而产生大体积收缩，因此次晶包晶钢的裂纹敏感性高。在连续冷却中，相变不同于平衡条件下的行为，例如过冷和包晶反应的扩展等。因此，我们考虑热力学，经验方程式和每个相中的碳扩散来开发新的相变模型，以进行预测连续冷却过程中的相变行为。在该模型中，次包晶钢的相变包括5个阶段，直到所有相都变为γ相为止。根据冷却速率计算出冷却过程中δ/γ界面的速度和相分数。γ相过冷和碳含量。结果表明，在dT期间，如果凝固以δ相结束_p，通过大量转化形成γ相。相反，如果包晶反应从液体开始，则γ相形成并通过扩散相变生长。在后一种情况下，在过高的过冷度或非常快的冷却速率下，可能会发生剩余δ相的大量转变。该分析表明，取决于次晶包晶钢的碳含量，存在几种不同的路径。

图形摘要

次晶包晶钢的相变。