【作者】 雷雪；

【导师】 顾剑锋；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 博士

【摘要】 随着计算机技术的迅速发展,热处理过程的计算机模拟越来越受到人们的重视,已经成为当前热处理过程研究和工艺设计中必不可少的重要部分。大锻件作为重要的装备零件,其质量和性能的要求越来越高。为满足需要,必须提高大锻件的热处理质量。由于大锻件的尺寸结构原因,传统以经验、定性方式制订热处理工艺过程已不能很好的满足需求。为节省人力物力财力,热处理的数值模拟作为一种新的工艺预测和制订方式出现在人们的眼前。对于大锻件,热处理过程的模拟对提高工件性能,降低变形和开裂倾向有着重要的意义。本文在充分考虑加热过程中瞬态问题、相变潜热问题、热物性参数与温度的关系以及温度场、组织场相互作用的情况下,运用MSC.MARC有限元软件建立加热过程的有限元计算模型,并根据淬火温度组织要求,设定了工艺优化原则,并对原有工艺进行的模拟分析。通过改变加热工艺中的升温速度、中间保温温度和保温时间等工艺参数,对不同尺寸的30Cr2Ni4MoV低压转子进行工艺优化。借助于计算机模拟,本文分析了阶梯加热过程中各工艺参数对加热过程中组织转变、均温情况和热应力大小的影响。结果表明:阶梯加热过程中的第一次升温速度能有效降低低压转子加热过程中产生的第一次最大温差和弹性状态下的最大热应力;中间保温温度的降低能降低第一次最大温差和最大热应力,但效果不甚明显;但其升高能有效降低第二次最大温差,减小表心部开始奥氏体化的时间间隔;第二次升温阶段的升温速度的增加会降低表面奥氏体化的时间,但对心部奥氏体化时间影响很小,同时会增加低压转子的均温时间。根据模拟获得的各工艺参数对加热过程的影响,本文分别对φ1 768mm和φ2826mm低压转子进行了加热工艺优化。优化后的工艺,总加热时间上分别增加了20.5和60小时,能保证加热结束时转子表心部温差不超过10℃,基本达到均温转子全部奥氏体化,并有效降低了加热过程中产生的最大热应力值。更多还原

【Abstract】 With the rapid development of computer technology, heat treatment computer simulation is receiving increasing attention, and has become an essential part in the process study and design of current heat treatment technology. As important equipment parts, the demand of large forgings’quality and performance are increasingly higher. To meet the needs, the heat treatment process of large forgings, a method to improve the forges performance, has to be improved. It is difficult to make out the proper heat treatment process by traditional empirical and qualitative method for the large forgings. So, in order to save resources, heat treatment simulation technology has appeared as a new solution way. For large forgings, heat treatment process is of great significance in improving the workpiece performance and reducing the deformation and cracking tendency.Completely considering the temperature field, the microstructure field and the internal stress field of the heating process, a FEM model of heating process has been built based on the software package MSC.MARC. Based on the quenching requirement for the temperature and microstructure, the optimization principles are set, and the old heating processes have been simulated and analyzed. The heating processes of LP rotors with different diameter have been optimized by altering different process parameters, such as heating rate, the middle holding temperature, holding duration, and so on.With the aid of computer simulation, the influence of different process parameters on the microstructure transformation, temperature uniformization and thermal-stress has been analyzed. The results show that: the heating rate of the first heating stage can effectively reduce the first largest temperature difference and the thermal-stress between the surface and center of the rotor; the reduction of the second holding step temperature can slightly reduce the first largest temperature difference and the thermal-stress,and its increasing can effectively decrease the second largest temperature difference and shorten the austenization beginning time gap between surface and center of LP roter; the austenization of the LP rotor is mainly related with the heating rate of the second heating stage, the higher the heating rate, the bigger time interval between austenization beginning time of the surface and center, and the more time needed to lessen the temperature difference between surface and center.Based on the simulation results, the heating process of LP rotor with the diameter of 1768mm and 2826mm are respectively optimized. Although the total heating time increases 20.6 and 60 hours respectively in the optimized heating process, the temperature difference between surface and center of LP rotor can be under 10℃,the whole rotor can be homogeneously austenized, and the biggest thermal-stress can be reduced effectively.更多还原