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。
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.
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