Calculation On Heat Transfer Coefficient Of Several Typical Steels In Different Quenchants

The heat transfer coefficient is considered as an objective and direct parameter to estimate the cooling ability of quenchants; On the other hand, it is an absolutely necessary boundary condition, especially in the simulation of the transient temperature field, phase transformation microstructure field, and thermal stress field. The results of the simulation depend much on the accuracy of the-heat transfer coefficient, and the reliable prediction of the properties of a heat-treated workpiece requires accurate data of the heat transfer coefficient during heat treatment process.In this thesis, inverse methodology instead of a direct approach has been applied to calculate heat transfer coefficient, based on the cooling curves of quenching experiment process in which 8 typical steels, namely, 45 steel, T8 steel, 42CrMo steel, 20CrMo steel, 20CrMnTi steel, GCr15 steel, 65Mn steel and 20 steel are quenched in different quenchants. With the nonlinear estimate method and the finite difference method, the calculation of the nonlinear synthetic surface heat transfer coefficient is carried out, which .is.coupled with phase transformation process of several typical steels during quenching. the continuous cooling phase transformation model is established, with the aid of the TTT diagram, the Scheil's sum principle and isothermal transformation kinetics. This thesis has analyzed and eompared the calculated results of the heat transfer coefficient.In order to verify the accuracy of heat transfer coefficient,2D nonlinear finite element axisymmetric model is established by the means of finite element (FE) software MSC.Marc, which is utilized to simulate the transient temperature field coupled with phase transformation process and nonlinear synthetic surface heat transfer coefficient of several typical steels in the different quenchants. And this thesis has compared the simulated value of 2D transient temperature field with the experimental value, the comparison results indicate that the simulated value and the experimental measured value fit comparatively well, and show that the obtained heat transfer coefficients have reasonable accuracy.