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金属学报  2014, Vol. 50 Issue (12): 1505-1512    DOI: 10.11900/0412.1961.2014.00317
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基于微观偏析模型的连铸方坯内裂纹敏感性研究
窦坤1, 卿家胜1, 王雷1, 张晓峰1, 王宝1,2, 刘青1(), 董洪标2
1 北京科技大学钢铁冶金新技术国家重点实验室, 北京100083
2 Department of Engineering, University of Leicester, Leicester, LE1 7RH, UK
RESEARCH ON INTERNAL CRACK SUSCEPTIBILITY OF CONTINUOUS-CASTING BLOOM BASED ON MICRO-SEGREGATION MODEL
DOU Kun1, QING Jiasheng1, WANG Lei1, ZHANG Xiaofeng1, WANG Bao1,2, LIU Qing1(), DONG Hongbiao2
1 State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083
2 Department of Engineering, University of Leicester, Leicester, LE1 7RH, UK
引用本文:

窦坤, 卿家胜, 王雷, 张晓峰, 王宝, 刘青, 董洪标. 基于微观偏析模型的连铸方坯内裂纹敏感性研究[J]. 金属学报, 2014, 50(12): 1505-1512.
Kun DOU, Jiasheng QING, Lei WANG, Xiaofeng ZHANG, Bao WANG, Qing LIU, Hongbiao DONG. RESEARCH ON INTERNAL CRACK SUSCEPTIBILITY OF CONTINUOUS-CASTING BLOOM BASED ON MICRO-SEGREGATION MODEL[J]. Acta Metall Sin, 2014, 50(12): 1505-1512.

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摘要: 

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(CR)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.

关键词 连铸方坯非均匀冷却微观偏析内裂纹敏感性    
Abstract

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 (CR) 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.

Key wordscontinuous casting bloom    non-uniform cooling    micro-segregation    internal crack susceptibility
    
ZTFLH:  TG244.3  
基金资助:* 国家自然科学基金项目51074023和钢铁冶金新技术国家重点实验室自主研发基金项目41602023资助
图1  Fe-C二元相图中的包晶凝固反应区[15]
Element d-Fe g-Fe
DS,i / (m2 ? s-1) mi / (℃ ? %-1) ki DS,i / (m2 ? s-1) mi / (℃ ? %-1) ki
C 7.9×10-9 80 0.20 6.4×10-10 60 0.35
Si 3.5×10-11 8 0.77 1.1×10-12 8 0.52
Mn 4.0×10-11 5 0.75 4.2×10-13 5 0.75
P 4.4×10-11 34 0.13 2.5×10-12 34 0.06
S 1.6×10-10 40 0.06 3.9×10-11 40 0.025
表1  钢中主要溶质元素的凝固参数[17]
Steel C Si Mn P S Fe
M1 0.13 0.35 1.52 0.016 0.002 Bal.
YQ450NQR1 0.09~0.14 0.30~0.50 1.25~1.40 ≤0.025 ≤0.015 Bal.
表2  参考文献[18]中M1钢及本研究YQ450NQR1钢的化学成分
图2  液相中P和Mn偏析情况预测值与实验值[18]对比
图3  YQ450NQR1钢方坯典型位置的冷却速率
图4  微观偏析模型计算流程图
图5  凝固过程中元素微观偏析规律
图6  冷却速率对溶质元素微观偏析的影响
图7  冷却速率对零强度温度、零塑性温度以及黏滞性温度的影响
图8  冷却速率与内裂纹敏感性系数的拟合曲线
图9  铸坯纵向切片皮下裂纹形貌
图10  铸坯凝固坯壳厚度随时间变化曲线
图11  铸坯裂纹产生位置冷却速率变化曲线
  符号说明
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