过热度对轴承钢凝固组织整体形貌特征及渗透率的影响  

Effect of Superheat on Integral Morphology Characteristics of Solidification Structure and Permeability in Bearing Steel Billet

作　　者：曹江海[1,2] 侯自兵 郭中傲[1,2] 郭东伟 唐萍 CAO Jianghai;HOU Zibing;GUO Zhongao;GUO Dongwei;TANG Ping(College of Materials Science and Engineering,Chongqing University,Chongqing 400044,China;Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials,Chongqing University,Chongqing,400044,China)

机构地区：[1]重庆大学材料科学与工程学院,重庆400044 [2]重庆大学钒钛冶金及新材料重庆市重点实验室,重庆400044

出　　处：《金属学报》2021年第5期586-594,共9页Acta Metallurgica Sinica

基　　金：国家自然科学基金委员会-中国宝武钢铁集团有限公司钢铁联合研究基金项目No.U1860101;重庆市基础科学和前沿技术研究专项项目No.cstc2017jcyjAX0019。

摘　　要：引入分形维数和比表面积对GCr15轴承钢连铸方坯的凝固组织整体形貌特征进行定量描述,并基于此计算枝晶通道的渗透率。结果表明,分形维数可描述凝固组织形貌的自相似复杂程度,比表面积可描述凝固组织的粗化程度。与高过热度(35℃)相比,低过热度(20℃)下生产的铸坯其分形维数较小,比表面积较大,且等轴晶区的渗透率较小;即低过热度时富集溶质的液相在枝晶间的流动阻力大,更有利于铸坯宏观偏析缺陷的控制。此外,为有效抑制高过热度时铸坯宏观偏析缺陷的形成,应在尽可能保证等温凝固的条件下通过调节工艺参数增大铸坯等轴晶区的冷却速率。As a typical bearing steel, GCr15 steel tends to solidify over a wide temperature range during casting because of its high carbon content. The size of the mushy zone is relatively large, causing macrosegregation and porosity defects in bearing steel. The morphology of the solidification structure plays an important role in governing macrosegregation severity. Solidification structures have conventionally been characterized by measuring the primary or secondary dendrite arm spacing in a dendritic network, but these measures do not adequately describe the branched appearance of secondary and tertiary arms. In this work, fractal dimension and specific surface area have been introduced, and the solidification structure integral morphology characteristics of different locations in the continuous casting billet of GCr15 bearing steel have been quantitatively investigated. Then, the permeability of the interdendritic channels were calculated based on fractal dimension and specific surface area. The size of the billets was 220 mm × 220 mm, and the sampling location was in the cross section of the billet. Two superheats(20 and 35 oC) were considered for studying the integral characteristics of the solidification structure. First,fractal dimension can describe the self-similar complexity of the solidification structure, and specific surface area can describe dendritic coarsening. Second, it was determined that the fractal dimension was larger and the specific surface area was smaller at 35 oC superheat compared with 20 oC superheat. This indicates that the self-similar complexity of dendrites is larger, and the dendrite coarsening is more significant at high superheating. Finally, the permeability in the equiaxed grain zone calculated using fractal dimension and specific surface area is lower at 20 oC superheat. The smaller the permeability, the greater the flow resistance of the liquid, which is more conducive to the control of the macrosegregation defects.In addition, to effectively restrain the formation of macrosegreg

关 键 词：过热度 凝固组织 分形维数 比表面积 渗透率 轴承钢 

分 类 号：TG113.12[金属学及工艺—物理冶金]