Comparative Analysis of Heat Transfer Characteristics During Quenching of EN9 steel:CFD and Experimental

Heat treatment is the process used for the alteration of physical properties of the material under treatment for their suitability of structural and functional requirement. The thermal simulation of the heat treating process is usually a transient type of temperature analysis, in which the hot metal part temperature changes with respect to time from an initial state to a final state. In the simulation, initial temperature of the hot part and temperature of quenchant are usually easy to obtain and can be assigned with reasonably accurate values. So are the thermo physical properties of the part material. The critical part is to determine the heat transfer coefficient between the hot part and quenchant. In liquid quenching, the heat transfer between hot metal parts and water is very complicated and it is difficult to determine the HTC. For this experimentation the EN 9 steel rod with Φ50 mm and length 100 mm along with water and ethylene glycol mixture with different concentrations as quenching medium are used. More and more attention is paid to numerical modelling using finite element packages and computational fluid dynamic packages for the benefits on money and time saving. A part model is created in 3-D form, then the model is meshed and by applying the actual boundary conditions the CFD analysis is conducted. In order to validate CFD analysis the experimental trials are conducted. In this paper the conducted experimental trials are discussed and compared with the CFD results. Keywords— Quenching, HTC, CFD, heat flux, cracking, and temperature gradient. I. INTRODUCTION In order to prevent the harmful effects of distortion, residual stress and cracking while improve the mechanical properties of steel alloy components, it is highly necessary for heat treaters to optimize component designs and heat treating processes. Experimental trials are used to determine better component designs and process setups, but more and more attentions are being paid to numerical modelling using finite element packages and computational fluid dynamic packages for the benefits on money and time saving. Numerical simulations of quenching of metal parts are usually carried out by finite element analysis packages such as ABAQUS, ANSYS, etc., a CAD model of the part needs to create in 2-D or 3-D form, then the model can be meshed with suitable elements. For quenching simulations, the temperature-displacement simulation is usually decoupled to thermal simulation and structure simulation in industrial practice for two reasons. First, decoupled simulation scheme requires less memory and converges faster than the coupled one. Second, the results from these two schemes are similar since in heat treating processes the heat generated by deformation is usually negligible compared to the heat transferred from hot solid to environmental media. Thus, thermal simulation needs to be first carry out to obtain temperature-time profile of the part. The followed structural simulation reads the temperature time profile and predicts quenching results such as distortion and residual stresses. In order to obtain high accurate simulation results, the finite element modelling must be validated by experimental measurements of residual stresses, distortion, etc. The thermal simulation of a heat treating process is usually a transient temperature analysis, in which the hot part temperature changes with respect to time from an initial state to a final state. In the simulation, initial temperature of the hot part and temperature of quenchant are usually easy to obtain and can be assigned with reasonably accurate values. So are the thermo physical properties of the part material. The biggest uncertainty is the heat transfer coefficient (HTC) between the hot part and quenchant. It has been reported that HTC affects the quenching result significantly.