系列模铸钢锭锭型优化设计及宏观偏析模拟

IMR OpenIR

	系列模铸钢锭锭型优化设计及宏观偏析模拟
	李娟
学位类型	硕士
导师	李殿中
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料工程
关键词	钢锭锭型宏观偏析计算机模拟多包延迟浇注 Steel Ingot Mold Design Macrosegregation Numerical Simulation Multi-concentration Delayed Pouring
摘要	"大型铸锻件的制造能力是衡量一个国家工业发展水平的重要标志，直接影响国家重型装备制造业和国民经济的发展。大型锻件是由大型钢锭锻造加工而成的，大型钢锭是大型锻件的先期产品，钢锭的质量直接影响甚至决定锻件的质量。由于钢锭内部存在多种类型的缺陷，致使钢锭制成锻件后的材料利用率很低甚至直接报废。研究钢锭内部缺陷的形成规律，开发降低钢锭内部缺陷的工艺、提高钢锭的生产质量对提高我国大型锻件的制造能力意义重大。钢锭内部的中心缩孔疏松缺陷和宏观偏析缺陷是对钢锭质量影响最大的两种缺陷。本文围绕大型钢锭的这两种主要缺陷，采用计算机模拟技术，通过研究钢锭的锭型结构对钢锭凝固过程的影响规律，优化设计相应钢锭的锭型，降低钢锭中心缩孔疏松缺陷的产生倾向；建立大型钢锭多包合浇过程中宏观偏析计算模型，研究大型多包合浇钢锭内部宏观偏析的形成规律，分析多包合浇工艺参数对宏观偏析形成的影响，并优化相关浇注工艺，将钢锭内部的宏观偏析控制在工业允许的范围内。论文的主要研究工作和结论包括：（1）利用有限元模拟软件ProCAST模拟计算钢锭的凝固过程，系统研究了冒口的高度、径缩比、锥度和锭身的锥度、高径比等锭型结构参数对钢锭凝固过程的影响规律，通过分析钢锭凝固过程的温度场，研究了钢锭凝固过程中糊状区形状的变化规律，预测钢锭内部中心缩孔疏松缺陷的产生倾向。研究发现，冒口对锭身的补缩作用十分重要，如果冒口参数不合理，则会导致冒口难以对锭身进行有效补缩，从而产生严重的缩孔疏松缺陷；冒口高度和冒口径缩比对冒口的补缩效果影响最为显著，冒口锥度影响相对较小。锭身锥度越大，凝固过程中糊状区的形状越宽、越浅，越有利于上部钢液对锭身进行补缩，从而有利于降低锭身缩孔疏松产生的倾向；锭身高径比较小的钢锭，凝固过程中糊状区的形状比较宽、浅，有利于锭身补缩，从而减少锭身的缩孔疏松缺陷。从保证钢锭质量并提高钢锭的利用效率的角度出发，优化设计了16-600t系列吨位模铸钢锭的锭型，建立了相应的锭型图谱。（2）建立了热-溶质对流情况下的多元合金钢锭宏观偏析计算模型，基于经典混合理论，采用连续介质模型推导出质量、动量、溶质和能量等宏观守恒方程，并构造了一个一元二次方程对固相分数进行求解。采用建立的模型成功模拟了Fe-C-Si-Mn四元合金360t多包合浇钢锭的凝固偏析行为，通过将模拟结果和实验测量结果对比，验证了所建立的模型准确可靠，可以用来模拟研究大型钢锭多包合浇过程中宏观偏析的形成。（3）利用所建立的偏析计算模型系统研究了多包合浇工艺参数对钢锭内部宏观偏析形成的影响规律。研究发现，传统的多包连续浇注工艺不能有效地减轻锭身的偏析，最后一包钢液的延迟浇注时间直接影响钢锭内部的偏析程度，尤其对锭身上半部分的正偏析具有显著的影响，本文据此提出了多包延迟浇注工艺。为了有效地控制锭身的偏析，需要设置合理的最后一包延迟浇注时间。如果延迟时间太长，锭身内部将出现“负-正-负-正”式的偏析分布，致使锭身化学成分分布不均匀；如果延迟时间太短，则减轻偏析的效果并不明显。模拟结果表明，最后一包的低碳钢液应该在中心轴线上的负偏析发展结束的时刻浇入。通过主要调节延迟浇注时间、辅助调节最后一包钢液的碳浓度和过热度，成功将360t钢锭的中心轴线碳偏析控制在工业允许的范围内，为相关钢锭的高质量生产制造提供了理论依据。
其他摘要	"The ability to manufacture high-quality heavy castings and forgings is a symbol of the development level of the heavy industry, and has a meaningful influence upon the further development of the equipment manufacturing industry and economics for a country. The heavy steel ingot, which is the raw material of the heavy forging, determines the quality of the heavy forging directly. Therefore, the existence of some defects in the steel ingot will lower the material utilizing efficiency and forging yield definitely. Thus, it is significantly meaningful to investigate the formation of the defects and develop the techniques to improve the quality of the steel ingot. Generally, the central shrinkage porosity and the macrosegregation, which are investigated in the paper, are the most important defects that influence the quality of the steel ingot. By numerical simulation, the influence of the mold design on the solidification process of the steel ingot is studied to optimize the mold design for reducing the central shrinkage porosity. In addition, a continuum mathematical model for the transport phenomena in the solidification systems has been established to study the formation of the macrosegregation in the multi-concentration pouring (MCP) steel ingot. The influence of the MCP parameters on the macrosegregation has been investigated and the pouring technique is optimized to control the macrosegregation in the steel ingot based on the simulation. The main contents and results in this study include: (1) The solidification process of the steel ingot has been simulated by the finite element simulation software ProCAST. The influence of the mold structural parameters on the solidification characteristics of the steel ingot has been reasonably investigated, according to the temperature distribution and the evolution of the shape of the mushy region. It is found that the hot top is very important for feeding the ingot body. The height of the hot top and the ratio of the hot top diameter to the ingot diameter rather than the taper of the hot top have remarkable effect on feeding the ingot body. In order to ensure fine feeding condition of the hot top, the height of the hot top and the ratio of the hot top diameter to the ingot diameter should be large enough. With a larger taper and a lower H/D of the ingot, the shape of the mushy region during the solidification is wider and shallower, which is better for feeding the ingot body and hence eliminating the central shrinkage porosity. When designing the mold shape in practice, it should both consider the solidification characteristics and the material utilization efficiency. The mold design should improve the utilizing efficiency as high as possible in the precondition of ensuring better solidification pattern of the steel ingot. (2) With the consideration of thermo-solutal convection, a mathematical model of macrosegregation simulation is established. The continuum model based on the classical mixed theory is used to rigorously derive the macroscopic conservation equations for mass, momentum, solute and energy. A quadratic equation of one variable (solid fraction) is developed to calculate the solid fraction. Based on the model, the solidification process of a Fe-C-Si-Mn 360t MCP steel ingot with the experimental processing parameters has been simulated. And the established simulation model is validated by comparing the simulation result with the experimental one, which indicates that the established model is reasonable and can be adopted to simulate the formation of the macrosegregation in the heavy steel ingot during the MCP process. (3) The influence of the MCP parameters on the formation of the macrosegregation has been investigated by the established model. It is found that the traditional MCP technique with no interval among ladles has no significant effect on reducing the macrosegregation in the heavy steel ingot, while the delay pouring time for the last ladle has remarkable influence on the macrosegregation distribution, especially for the positive segregation below the hot top. Based on the simulation results, an innovative multi-concentration delayed pouring (MCDP) technique is proposed in this paper. In order to effectively reduce the macrosegregation, a proper delay time for the last ladle should be primarily determined. If the delay time is too long, the Negative-Positive-Negative-Positive style segregation appears. If the delay time is too short, the positive segregation cannot be reduced noticeably. The last ladle should be poured at the moment when the segregation along the centerline turns from negative to positive. Finally, with the delayed pouring technique with proper parameters, the carbon concentration along the centerline in the ingot body is controlled within the industrial limitation and the macrosegregation distribution is improved remarkably in the 360 t steel ingot.
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64548
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	李娟. 系列模铸钢锭锭型优化设计及宏观偏析模拟[D]. 北京. 中国科学院金属研究所,2012.