【作者】 郑泽花；

【导师】 张立文；

【作者基本信息】 大连理工大学 ， 材料学， 2010， 硕士

【摘要】 淬火是改变和提高金属材料性能的重要手段。近几十年来,学者对淬火过程进行了大量的研究,而计算机模拟技术因其能够优化工艺、降低废品率、提高工作效率而成为非常有效的研究方法。淬火是涉及热、力、组织及其相互作用的复杂过程,对这一过程的模拟主要包括边界条件和各种热物性参数的测算、模型的建立、对计算结果的验证等。本论文根据反传热思想和实测的几种典型钢探头在多种介质中淬火时的冷却曲线,建立了耦合相变的轴对称有限差分模型,用FORTRAN语言编程计算钢探头淬火过程的表面综合换热系数。结果表明,考虑相变时计算得到的换热系数比不考虑相变时的计算值要大,而且考虑相变时的计算结果被证明更加合理和准确。同时发现,相同探头淬火过程的换热系数随淬火介质种类不同而变化,同一淬火介质对不同材料的探头的冷却能力也不同,即淬火过程的换热系数与淬火介质及探头材料均相关。以大型有限元软件MSC.MARC作为模拟平台,建立了淬火过程三维非线性分析模型,借助MSC.MARC的二次开发功能编写模拟相变过程的程序,以计算得到的非线性表面综合换热系数为边界条件,模拟了淬火过程中的瞬态温度场和组织场。模拟中把相变潜热作为每个单元的内热源,迭代求解中修正温度场,以提高计算精度。结果显示,淬火探头测温点的模拟冷却曲线与实测曲线吻合较好；组织模拟结果与实验金相照片的比较,说明模拟的组织场较接近真实淬火组织。上述结果说明利用本文所建模型能够对淬火工件温度场和组织场进行较为准确的模拟。本论文还用有限元软件DEFORM建立2D和3D模型,模拟42CrMo支重轮、42CrMo轴等大工件淬火过程的温度场和组织场。42CrMo支重轮在不同介质中淬火得到的组织不同,按照水淬油冷工艺淬火后,支重轮在组织性能上能够达到要求；42CrMo轴在同种介质中的淬硬层深度随工件尺寸而变化。更多还原

【Abstract】 Quenching as an important means of improving the mechanical properties of steel materials has been researched widely in recent years. The numerical simulation technique has become an efficient method to study quenching process, because it can optimize process, reduce the numbers of rejects and improve worked efficiency. The quenching of steels is a complex process that involves thermal, mechanical, and structural phenomena and their couplings. The simulation of quenching mainly includes the calculation of boundary conditions and thermophysical property parameters, the establishment of models, and the verification of calculation results.In this essay, axisymmetric finite-difference model with phase transformation was developed according to the inverse heat conduction method and the cooling curves. Surface heat transfer coefficients for several typical steels quenched in quenchants have been estimated with the designed FORTRAN program. The obtained surface heat transfer coefficient is larger and more reasonable while phase transformation is taken into account. It is also found that surface heat transfer coefficients for the same steel probe during quenching vary with the kind of quenchant, and the cooling capacity of a coolant medium cooling steel probes made of different materials is different. The results prove that surface heat transfer coefficients depend on both the type of quenchant and the material of steel probe.Taken surface heat transfer coefficients calculated above as boundary condition, a 3D nonlinear analysis model was presented by using the FE software MSC.MARC. The coupling between temperature and phase transformation was taken into account in the model. The simulation subroutine of phase transformation during quenching was developed, and the latent heat of phase transformation was treated as internal heat source which was added to each volume element to correct the calculated temperature field.The transient temperature field, the microstructure field of several typical steels during quenching were simulated with the FE model established above. The calculated cooling curves are in good agreement with the measured ones, and the simulated microstructure results have been compared with the metallographic graphs and verified reasonable. The above results show that it is capable of predicting the transient temperature field and microstructure field accurately with the model developed in this thesis.Also 2D and 3D models were established by using the FE software Deform, which were used to simulate the temperature and microstructure fields of large-scale 42CrMo shafts, 42CrMo thrust during quenching. The simulation results show that microstructures of the same large-scale 42CrMo thrust quenching in water and super-oil respectively are different from each other, and the microstructures and properties of 42CrMo thrust could satisfy the real requirements after quenching in water first and then cooling in super-oil. The depth of hardening zone varies with the size of large-scale 42CrMo shafts during quenching.更多还原