建立了YQ450NQR1钢连铸方坯的微观偏析模型, 研究了在不同冷却速率的凝固过程中钢中主要溶质元素C, Si, Mn, P和S的晶间偏析行为及其对固-液两相区特征温度, 即零强度温度(zero strength temperature, ZST), 零塑性温度(zero ductility temperature, ZDT)及黏滞性温度(liquid impenetrable temperature, LIT)的影响. 在此基础上定义了内裂纹敏感性指数(IICS), 并对YQ450NQR1钢连铸方坯内裂纹敏感性进行了表征. 结果表明: IICS值越趋近于1, 铸坯内裂纹敏感性越大. 此外, 还建立了描述IICS与冷却速率(C_R)关系的内裂纹敏感性模型, 并对其进行验证, 结果表明, 该模型能够定量描述非均匀冷却条件下YQ450NQR1钢连铸方坯的内裂纹敏感性.

The solidification and cooling of liquid steel in continuous casting process is a complicated non-equilibrium phenomenon. During steel solidification process, the micro-segregation of solute elements between liquid steel and solidified shell will vary with their temperature-dependent diffusion coefficients and equilibrium distribution coefficients. Due to non-uniform cooling pattern in the continuous casting process of steel blooms, the fluctuation of cooling rate in bloom will have a great influence on micro-segregation degree of the elements. The micro-segregation behavior of solute elements in steel solidification process is responsible for the variation of characteristic temperatures such as zero strength temperature (ZST), zero ductility temperature (ZDT) and liquid impenetrable temperature (LIT), which make up the brittle temperature range in steel solidification. During continuous casting process of steel, internal cracks created by thermal and mechanical deformation tend to occur in this range. To prevent the occurrence of these cracks in continuous casting bloom, it is essential to better understand about the internal crack susceptibility concerning micro-segregation behavior in the non-uniform cooling process. In this work, a micro-segregation analytical model for YQ450NQR1 steel continuous casting bloom is established to study the inter-dendritic segregation behavior of main solute elements C, Si, Mn, P and S at various cooling rates, the results show that P and S are more likely to segregate compared with C, Si and Mn and the increase of cooling rate weakens the micro-segregation degree of C, Si, Mn, P and S. Based on the micro-segregation model established above, ZST, ZDT and LIT for YQ450NQR1 steel are calculated and the influences of cooling rate on ZST, ZDT and LIT are analyzed. It reveals that ZST, ZDT and LIT of YQ450NQR1 steel bloom decrease accordingly with the increase of cooling rate. On this basis, the index of internal crack susceptibility (IICS) is defined to quantitatively characterize the internal crack susceptibility of the bloom. The results show that the internal crack susceptibility becomes larger while the IICS value approaches to 1. Furthermore, an internal crack susceptibility model is obtained concerning IICS and cooling rate (C_R) and the validation is performed to certify the model′s suitability in quantitatively predicting internal crack susceptibility of YQ450NQR1 steel continuous casting bloom in the non-uniform cooling process.