百吨级钢锭缩孔疏松预测与工艺优化

IMR OpenIR

	百吨级钢锭缩孔疏松预测与工艺优化
	王佳琪
学位类型	硕士
导师	李依依 ; 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	材料加工工程
关键词	大型锻造用钢锭轴线缩孔疏松有限元数值模拟工艺优化 Heavy Forging Ingots Centerline Shrinkage Porosity Fem Simulation Optimized Design
摘要	"大型铸锻件是国家重大工程的核心部件，其制造能力是衡量一个国家工业发展水平的重要标志。但是，我国冶金机械、能源电力、船舶制造、石油化工等领域的大型铸锻件曾长期依赖进口，受制于人。大型钢锭是大型锻件的坯料，制备优质大型钢锭是实现国家重大装备用大型锻件自主生产的关键。而缩孔疏松是大型钢锭最常见的内部缺陷之一，严重影响大型钢锭的质量。本文采用有限元模拟和钢锭实际浇注、解剖实验相结合的方法，对100吨30Cr2Ni4MoV核电低压转子用钢锭的铸造过程进行系统研究。通过优化有限元计算模型，提出合适的预测其轴线缩孔疏松的判据，并在此基础上提出系列工艺改进准则。在合作企业成功浇注了“最优工艺”条件下的100 t钢锭，基本消除其轴线缩孔疏松缺陷，并把该判据和工艺优化准则推广到系列大型锻造用钢锭（90 - 600 t）的铸造工艺中，基本解决了大型锻造用钢锭轴线缩孔疏松缺陷的问题。论文的主要研究内容和结论包括： 1) 总结了铸造过程中传热模型、流动模型和应力计算模型，探讨了各方程的数值求解方法。在企业实际浇注了100吨30Cr2Ni4MoV核电低压转子用钢锭，并对其进行解剖分析，通过超声波探伤等实验确定其轴线缩孔疏松缺陷的分布和尺寸。基于实际解剖实验结果，优化大型钢锭计算模型和有限元模拟的初始、边界条件。并利用商业有限元软件ProCAST初步模拟100 t钢锭铸造过程中流场、温度场、应力场等信息。 2) 通过100 t钢锭有限元模拟，解释其轴线缩孔疏松缺陷的产生机理。在此基础上研究了不同缩孔疏松判据，提出G/Rs0.5＜临界值判据可以作为大型钢锭轴线缩孔疏松的优化判据（其中G为温度梯度，Rs为凝固速度），由此判据得到的钢锭轴线缩孔疏松的尺寸和分布结果与实际钢锭超声波探伤结果符合良好。把该判据用到135 t和234 t钢锭的有限元模拟中，轴线缩孔疏松的计算结果与文献中解剖结果吻合，进一步验证了所提出判据的通用性。 3) 总结大型钢锭锭型工艺设计方法，在此基础上，对100 t钢锭提出系列工艺改进措施，并系统研究了每一种工艺改进措施对其轴线缩孔疏松的影响。模拟结果表明，使用“最优工艺”可以基本消除100 t钢锭的轴线缩孔疏松缺陷。在此基础上把研究100 t钢锭所使用的缩孔疏松判据和工艺优化准则推广到系列大型钢锭（90 - 600 t）中，基本消除了大型钢锭轴线缩孔疏松缺陷。最后，在工厂成功浇注“最优工艺”条件下的100 t钢锭，并对其进行实际解剖和探伤实验，结果表明，“最优工艺”基本消除钢锭轴线缩孔疏松缺陷，其当量可控制在φ3mm以下，达到锻件GB/T 6402-1991 二级探伤水平。"
其他摘要	"The heavy castings and forgings are the core parts of the state project, and the ability to manufacture them is the symbol of the industry development level of the country. However, the heavy castings and forgings of the metallurgical machinery, energy, electric power, shipbuilding, and petrochemical field in our country have been relied on imports for a very long time. As the raw material of the heavy forgings, the heavy steel ingots determine the quality of the final products. However, the shrinkage porosity is one of the most common defects of the heavy ingots, which influences the quality of the ingots. In this work, through FEM simulation in combination with the experimental sectioning investigation of the 100 ton 30Cr2Ni4MoV ingot, the whole casting processes of the ingot have been systematically studied. The finite element model of the heavy ingot has been optimized and a criterion which can be used to reproduce precisely the experimental size and distribution of the centerline shrinkage porosity in heavy steel ingots has been successfully proposed. Based on the proposed criterion, the techniques have been redesigned and optimized to fabricate the 100 t ingot with an aim of improving the quality by eliminating the shrinkage porosity. Furthermore, the optimized design standard of the 100 t ingot has been expanded to the series heavy ingot (90 - 600 t) to solve their centerline shrinkage porosity problem. The main contents and results in this study include: 1) The simulation model of the heat transfer, flow, and stress has been summarized, and the numerical solution method of the equations has been briefly discussed. A 100 ton 30Cr2Ni4MoV ingot has been fabricated, and then it has been cut along the axle plane and analyzed to observe the distribution and size of shrinkage porosity in the ingot. Based on the experimental results, the finite element model, initial and boundary conditions have been optimized. The flow, temperature and stress field of the casting process of the 100 t ingot have been preliminary simulated by the commercial FEM software ProCAST. 2) Through the FEM simulation of the 100 t ingot, the mechanism of centerline shrinkage porosity has been clarified. Based on the experimental result and FEM simulation, several criteria of the centerline shrinkage porosity have been discussed. It has been investigated that the criterion G/Rs0.5＜constant, where G and RS are the temperature gradient and solidification rate, respectively, can serve as the best criterion to predict the centerline shrinkage porosity of the heavy ingots. The theoretically simulated distribution and size of the shrinkage porosity agree well with the experimental results observed by the sectioning and ultrasonic testing. When this criterion has been applied to the centerline shrinkage porosity simulation of the 135 t and 234 t ingots, it can also be found that the simulation results are consistent with the experimental results from literatures, which further demonstrates the generality of the criterion. 3) Summarize the optimized methods of the heavy ingots. Based on these methods, the series optimized designs of the 100 t ingot have been proposed, and the effect of each parameter on the centerline shrinkage porosity has also been discussed. By utilizing the “best design” of the 100 t ingot, the simulation results uncovered that the centerline shrinkage porosity could be nearly eliminated. Meanwhile, the methods used in the 100 t ingot can also be applied to the series heavy ingots (90 - 600 t) and improving their quality. At last, the 100 t “best design” ingot has been fabricated in the factory, and the sectioning and ultrasonic results shows that the centerline shrinkage porosity equivalent defects can be reduced to lower than φ3mm and the quality of the ingot is fairly good ."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64534
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王佳琪. 百吨级钢锭缩孔疏松预测与工艺优化[D]. 北京. 中国科学院金属研究所,2012.