SWRH 92A帘线钢中异相形核TiN复合夹杂析出机制

摘要：高碳帘线钢中析出的非金属夹杂物如钛夹杂，对钢材疲劳强度影响巨大。系统分析过共析帘线钢中钛夹杂的析出行为对控制夹杂物形成及产品质量提升尤为重要。结合形核理论以及热力学耦合模型，对SWRH 92A帘线钢盘条存在的Al2O3 TiN复合夹杂物的形成机制进行了研究。结果表明：TiN夹杂在钢液凝固进程凝固分数约为0.866(温度为1457K)时开始析出；凝固前期Ti、N偏析比基本相当，然而当凝固接近结束时Ti的偏析比明显大于N，分别为6.059和2.367×10-6。TiN夹杂物形成过程中，其异相形核功小于均相形核功，异相形核半径大于均相形核半径，并且形核功与形核半径变化曲线在1457K时均达峰值。呈球形形态的Al2O3夹杂在TiN析出之前就已经析出，并且尺寸较小的Al2O3将被推动至凝固前沿被TiN捕获并以此为核心析出长大最终形成Al2O3 TiN复合夹杂。

Precipitation mechanism of heterogeneous nucleation of TiN composite inclusions in SWRH 92A tire cord steel

Abstract： Non-metallic inclusions, such as Ti bearing inclusions, existed in high carbon tire cord steel have significant impacts on steel fatigue strength. Systematic investigation of the precipitation behavior of such inclusions in eutectoid tire cord steel is very important for inclusion precipitation management and product quality improvement. The precipitation behavior of Al2O3 TiN composite inclusions in steel was analyzed by using the nucleation theory and thermodynamic coupling model. The results show that TiN inclusions begin to precipitate when the solidification fraction of molten steel is about 0.866 (at 1457K). The segregation ratio of Ti and N is basically the same at the early stage of solidification; and in the late stage of solidification, however, the segregation ratio of Ti is significantly greater than that of N, which are 6.059 and 2.367×10-6, respectively. The heterogeneous nucleation work of TiN inclusion is smaller than its uniform nucleation work; however, its heterogeneous nucleation radius is larger than its uniform nucleation radius; besides, both the nucleation work and nucleation radius reach the maximum value at 1457K. The spherical shaped Al2O3 inclusion has been formed before TiN precipitate, and the smaller Al2O3 will be pushed to the solidification front to be captured by TiN. The preferentially formed Al2O3 could be acted as a core for the subsequent precipitated TiN, and then they will grow up gradually to form the final Al2O3 TiN composite inclusion.