Numerical Calculation Of Surface Heat Transfer Coefficient And Simulation On Temperature And Microstructure Of Steels During Quenching Process

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.