几种铸锻件热处理变形的模拟与实验研究

IMR OpenIR

	几种铸锻件热处理变形的模拟与实验研究
	程柏松
学位类型	博士
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	变形有限元模拟界面换热系数被动轴 Distortion Finite Element Simulation Interfacial Heat Transfer Coefficient Driven Shaft
摘要	"变形是工件热处理过程不可避免的现象。对大型工件而言，为避免工件热处理后尺寸不足，往往预留过大加工余量，致使材料利用率降低；对精密零件、工模夹具等来说，常因热处理变形而耗费大量工时进行校正和修整，变形过大的经常报废。影响热处理变形的因素很多，如材料的组织不均匀、工件的加热和冷却不均以及内部的残余应力作用等，变形往往是组织应力和热应力综合作用的结果，很难通过一个或几个影响因素的控制来根本解决变形问题。淬火变形作为热处理过程中最常见的变形方式，掌握其变形规律，对指导生产实践具有重要的意义。为此，本文采用有限元模拟和实验相结合的方法对淬火变形进行了研究。论文的主要研究内容包括： 1) 针对316奥氏体不锈钢及马氏体不锈钢ZG04Cr13Ni4Mo的淬火变形，本文实测了两种钢在不同温度下的比热、热导率、线膨胀系数、密度以及杨氏模量、泊松比等热物性参数。在实测应力—应变曲线的基础上，建立了两种材料的本构模型，这些数据为有限元模拟奠定了基础。 2) 采用DEFORM-3D软件建立了316奥氏体不锈钢C型环和纵切圆柱水冷淬火过程的三维有限元模型，研究了界面换热系数对变形模拟结果的影响。结果表明，变形模拟结果对界面换热系数的变化非常敏感。采用高采集频率下的界面换热系数，淬火后C型环缺口的尺寸将减小，纵切圆柱发生圆面一侧凹进，平面一侧凸起的弯曲变形；采用低采集频率下的界面换热系数，淬火后C型环缺口的尺寸将增大，纵切圆柱几乎不变形。高采集频率下的界面换热系数，模拟结果与实验结果吻合良好。界面换热系数高温段的差异，影响了淬火过程塑性变形量的计算，进而影响最终的变形结果。 3) 基于DEFORM-3D软件的热处理相变模型，建立了马氏体不锈钢ZG04Cr13Ni4Mo纵切圆柱淬火过程的三维有限元模型。结果表明，工件的变形过程经历了先向平面，再向圆面一侧的弯曲变形。淬火过程由于发生马氏体转变，在组织应力作用下，平面一侧产生较大拉伸塑性变形，导致变形结果为平面一侧凸起，圆面一侧凹进，模拟结果与实验结果吻合较好。采用文献的界面换热系数，变形结果与实验结果相反。 4) 在上述模拟结果的基础上，针对被动轴20Cr2Ni4A钢淬火及回火处理的变形过程进行了模拟。研究结果表明，淬火方式对变形模拟结果的影响很大，倾斜淬火是导致被动轴发生弯曲变形及圆跳度增加的直接原因。结合被动轴的实际热处理状况，对被动轴的淬火方式提出了改进意见。淬火过程应始终保持轴向与淬火介质的液面相垂直，对配套的工装应定期检查，避免精度不足影响正常的垂直淬火。在倾斜淬火引起较大弯曲变形的前提下进行回火处理，结果表明，低温回火对变形几乎没有影响。"
其他摘要	"Distortion of the workpiece during heat treatment is an inevitable phenomenon. An excessive machining allowance is often reserved for large workpiece, which leads to waste of materials. For precision parts, much time is needed to recorrect distortion. If distortion of the workpiece is too excessive, the workpiece will have to be abandoned. There are many factors that may induce distortion during heat treatment, such as non-uniform microstructure of the materials, non-uniform heating of the workpiece or residual stress, etc. Usually, distortion of the workpiece after heat treatment is caused by the comprehensive action of thermal stress and structural stress. Therefore, it is difficult to solve the problem of distortion only by controlling one or few factors. Since distortion is widely seen in quenching process, understanding of distortion mechanism during quenching process has an important practical significance. Using simulation and experimental methods, this paper investigates the quenching distortion. The main research work of this paper is as follows: 1) Both 316 austenitic stainless steel and ZG04Cr13Ni4Mo martensitic stainless steel are chosen to measure quenching distortion. The specific heat, thermal conductivity, linear expansion coefficient, density, young’s modulus, poisson ratio and other thermophysical parameters of the two kinds of steel are measured using experiments. The constitutive model of these two stainless steels is established based on the stress-strain curve. These data lay basis for the finite element simulation. 2) Deform-3D software is employed to establish three dimensional models of 316 austenitic stainless steel C-ring and cut-cylinder. The effect of IHTC (Interfacial Heat Transfer Coefficient) on distortion simulation results is investigated. The results indicate that distortion simulation results are sensitive to the accuracy of IHTC. If high frequency acquired IHTC is used, the gap of C-ring decreases, and the round surface of cut-cylinder is concaved while the plain surface of cut-cylinder is convex after quenching. If low frequency acquired IHTC is used, the gap of C-ring increases, and distortion of cut-cylinder is negligible. The simulation results using high frequency acquired IHTC is consistent with the experimental results. The accuracy of IHTC in high temperature stage affects the final distortion results by affecting plastic deformation during quenching. 3) Deform-3D software is employed to establish three dimensional finite element model of ZG04Cr13Ni4Mo martensitic stainless steel cut-cylinder. The results show that the distortion of workpiece first happens toward the plane and then toward the round surface. Martensitic transformation happens during quenching, which will lead to structural stress. Due to structural stress, the plain surface of cut-cylinder has tensile plastic deformation, which cause the plain surface becomes convex and the round surface to concave. These simulation results fit well with the experimental results. While the IHTC in the iterature is adopted, the simulated results reverse to the experimental results. 4) Based on the above simulation results, the distortion of a 20Cr2Ni4A steel driven shaft after quenching and tempering is simulated. The results suggest that quenching methods have great influence on the simulation results. If the workpiece is tilted with some angle, it will cause bending deformation and round-section surface deformation on the driven shaft. An improved quenching method is proposed that the axis of the driven shaft should be vertical to the surface of the liquid. Frock should be checked regularly to insure its accuracy. The simulation results show that if bending deformation already happens, tempering has little effect on distortion."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64444
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	程柏松. 几种铸锻件热处理变形的模拟与实验研究[D]. 北京. 中国科学院金属研究所,2012.