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金属学报  2017, Vol. 53 Issue (7): 769-777    DOI: 10.11900/0412.1961.2016.00426
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基于分形维数的模具钢电渣重熔铸坯碳偏析形貌特征研究
侯自兵(),曹江海,常毅,王伟,陈晗
重庆大学材料科学与工程学院 重庆 400044
Morphology Characteristics of Carbon Segregation in Die Steel Billet by ESR Based on Fractal Dimension
Zibing HOU(),Jianghai CAO,Yi CHANG,Wei WANG,Han CHEN
College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
全文: PDF(1595 KB)   HTML
  
摘要: 

引入分形维数,从面积数目与轮廓形貌2个方面对铸坯内不同位置的偏析特征展开定量化分析。结果表明,铸坯的整体偏析程度主要受大偏析点影响,且大偏析点越大或越多,偏析率越大;铸坯内偏析点形貌具有分形特征,且分形维数可以作为衡量区域内偏析点弥散程度的一个重要指标,即分形维数越大,偏析点分布越为弥散,大偏析点逐渐向小偏析点转变;在柱状晶等轴晶转变区与凝固终点等轴晶区,偏析点的分形维数相对较小。

关键词 偏析分形维数模具钢电渣重熔    
Abstract

Macro/semi-macro carbon segregation plays a key role for improving the steel product quality. Based on macrostructure qualitative rating comparison and element macro content analysis, the segregation extent has been controlled at different levels by the existing technologies, but there is an obvious shortcoming on segregation morphology description. Nowadays, delicacy control is demanded for higher quality requirement, especially for the production of high-quality H13 die steel by electro-slag remelting (ESR) technique. In this work, as to segregation point morphology, fractal dimension is introduced, and segregation characteristics of different locations in the ESR billet are quantitatively investigated in terms of area, number and outline morphology. The size of the billet is 160 mm×160 mm, and the sampling location in the central plane of billet. Two melting rates (350 and 400 kg/h) are considered for studying essential characteristics of segregation. Firstly, it is shown that the whole segregation extent in the billet is mostly influenced by the large segregation point (e.g., the area is larger than 0.1 mm2). The segregation ratio will be increased when increasing the number or area of the large segregation point. Secondly, it is found that fractal is a very important characteristic of the segregation point morphology in the billet. Moreover, fractal dimension can be used as a criterion for measuring the dispersion degree of the segregation. The dispersion degree will be increased when increasing the corresponding fractal dimension, and the large segregation point will be disintegrated by the small segregation point. Finally, the fractal dimensions in the columnar-equiaxed transition area and the solidifying end equiaxed area are less than the value of other locations. In addition, more researches are needed for accurately obtaining the influence factors of fractal dimensions of segregation point in the future.

Key wordssegregation    fractal dimension    die steel    electro-slag remelting
收稿日期: 2016-09-26      出版日期: 2017-05-10
基金资助:国家自然科学基金项目No.51504047和中央高校基本科研业务费项目No.CDJPY14130001

引用本文:

侯自兵,曹江海,常毅,王伟,陈晗. 基于分形维数的模具钢电渣重熔铸坯碳偏析形貌特征研究[J]. 金属学报, 2017, 53(7): 769-777.
Zibing HOU,Jianghai CAO,Yi CHANG,Wei WANG,Han CHEN. Morphology Characteristics of Carbon Segregation in Die Steel Billet by ESR Based on Fractal Dimension. Acta Metall, 2017, 53(7): 769-777.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2016.00426      或      http://www.ams.org.cn/CN/Y2017/V53/I7/769

图1  铸坯中心纵断面取样位置示意图
图2  I、II、III 3类不同大小偏析点示意图
图3  熔速为350 kg/h时铸坯内部不同位置的低倍组织
图4  熔速为400 kg/h时铸坯内部不同位置的低倍组织
图5  不同熔速下不同位置的偏析率
图6  不同位置I、II、III 3类偏析点的面积比
图7  不同位置I、II、III 3类偏析点的数目比
图8  偏析率与I类偏析面积比和数目比的变化关系
图9  熔速为350 kg/h时1#试样lnP-lnA关系图
Sample No. 350 kgh-1 400 kgh-1
D R2 D R2
1 1.799 0.9779 1.822 0.9109
2 1.760 0.9807 1.779 0.9697
3 1.760 0.9818 1.769 0.9688
4 1.755 0.9820 1.786 0.9731
5 1.760 0.9761 1.785 0.9729
6 1.747 0.9724 1.790 0.9704
7 1.757 0.9738 1.775 0.9726
8 1.755 0.9783 1.796 0.9718
9 1.762 0.9823 1.804 0.9701
10 1.742 0.9841 1.788 0.9719
11 1.735 0.9824 1.781 0.9651
12 1.767 0.9787 1.793 0.9680
表1  不同熔速下不同位置的分形维数D及对应的拟合系数R2
图10  不同熔速下不同位置的分形维数
图11  偏析率、偏析点平均面积与分形维数的关系
图12  熔速为350和400 kg/h时I、II、III 3类偏析点面积比与分形维数的关系
图13  熔速为350和400 kg/h时I、II、III 3类偏析点数目比与分形维数的关系
图14  熔速为350和400 kg/h时不同位置偏析点总数目与分形维数的关系
图15  铸坯内不同位置的局部凝固时间
图16  分形维数与局部凝固时间的关系
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