【作者】 林继辉；

【导师】 李国军；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2010， 硕士

【摘要】 淬火过程的计算机模拟可以实现对淬火质量的控制与预测,正在日益受到人们的重视。与传统实验相比,模拟/仿真实验具有灵活、快速、低价等优点,可以大大降低试验成本,缩短试验周期?本文基于传热学和相变学的基本原理,以热弹塑性本构方程为基础,以40Cr钢和60Si2Mn钢顶端淬火实验研究对象,使用大型热处理软件COSMAP对试件在不同奥氏体化温度下的顶端淬火冷却过程进行了计算机模拟。文中着重模拟预测了它们的三维淬火瞬态温度场、组织场、应力场及硬度,同时对同一种材料提高奥氏体化温度后淬透性变化进行了预测。结果得出:1、在温度场模拟时,应用流场项的三维各项同性体中瞬态温度场指数坐标系的偏微分方程计算温度场,同时设定了实际过程中的初始条件及边界条件,综合考虑了边界换热系数、相变潜热以及热物性参数等非线性因素的影响,大大减小了通用有限元软件处理淬火过程非线性问题时只能以常数代替所引起的模拟误差;为提高模拟精度及节省计算时间,本文采用了对模型表面单元格细分及变时间步长等方法。采用等效比热容法处理相变潜热,提高了温度场的计算精度。2、顶端淬火组织转变的过程是连续冷却过程,所以本文借助于Scheil的相加性原理,假定相变速率为转变量及温度的函数对连续冷却进行处理,即时间进行离散,将连续冷却等效转变为阶梯冷却,对于每个离散段时间可以按等温转变处理。本文在把TTT曲线输入计算机时,采用线性回归的方法对所涉及到的40Cr钢及60Si2Mn过冷奥氏体等温转变曲线(TTT曲线)进行分段处理,通过ORIGIN软件拟合出了等温转变曲线线性回归方程参数。在计算组织转变量时,使用Avrami模型计算扩散型等温转变相变量时;使用Inoue模型(Magee模型的修正式)对马氏体相变进行计算。3、在应力场的模拟计算中,充分考虑了材料的性质随温度和时间的变化、加工硬化以及相变塑性等因素的影响。4、最后本文通过顶端淬火实验硬度的测定、金相组织观察、及与已发表文献数据对模拟的结果进行了验证,吻合较好。更多还原

【Abstract】 Computer simulation of quenching process can be achieved on the quenching quality control and prediction, much attention is being increasingly. Compared with the traditional test, simulation / simulation experiment is flexible, fast, low-cost., it can significantly reduce the test cost and shorten the test cycle.1、This article is based on theories of thermodynamics and phase transofmration, and thermal elastic-plastic constitutive equation, with 40Cr steel and steel 60Si2Mn quencheing experiments as the research objects. Calculations are carried out to simulate the top of quenching process of specimens at different temperature austenitizing by using large heat treatment software COSMAP. The paper focuses on simulation and prediction of specimens three-dimensional transient temperature field quenching, organizational field, stress field and hardness, while prediction of the changes in hardenability as the same material imcreasing austenitizing temperature.In temperature field simulation, Applicating partial differential equations of index frame of the transient temperature field items in the three-dimensional flow field of the same-sex body calculate the temperature field. while setting the initial conditions and boundary conditions of the actual process,and considering the impact of the nonlinear factors such as the boundary heat transfer coefficient, latent heat and thermal properties parameters, greatly reduces simulation error when dealing with nonlinear problems of the quenching process by using the finite element software only can be replaced by the constant. To improve simulation accuracy and save computation time, using the surface of the cell model and variable time-step breakdown of other methods in this paper. using the equivalent heat capacity method deals latent heat raise the temperature accuracy.2、Quenching process is a continuous cooling transformation, therefore this means of Scheil’s additivity principle, dealing with the continuous cooling while assuming that changes in volume and phase shift was a function of temperature, that time discrete equivalent of continuous cooling transformation cooling for the ladder, for each discrete period of time can change by isothermal treatment. In this paper, the TTT curve of input computer, the method of linear regression involved the 40Cr steel and 60Si2Mn undercooled austenite isothermal transformation curve (TTT curve) for partition processing, fitted out by ORIGIN software isothermal transformation the linear regression equation parameters. In calculating the amount of organizational change, the use of diffusion Avrami model with variables such as temperature changes; using Inoue model (Magee model Modified) is calculated on the martensitic transformation. 3、In the stress field simulation, the full consideration of the material the nature of the changes with temperature and time, phase transformation hardening, and plastic and other factors.4、Finally, the top quenching experiments by the determination of hardness, microstructure observation, and with published literature data on the simulation results are verified, in good agreement.更多还原