External Magnetic Field Quenching Of The Transient Temperature Field And Computer Numerical Simulation Of Phase Transitions

In this paper, according to the priciple of heat transfer, thermal non-elasticity theory, phase transformation theory and electromagnetic theory, the mathematical model of numerical simulation of temperature field and phase transformation during the quenching process by the additional magnetic field was established. The computer program was drawn up.In the calculation of temperature field, we take the effect of the extra magnetic field as an additional energy item, taking advantage of the abnormal phenomena of specific heat of iron-magnetism nearby the Curie temperature, and establish the heat conduction eqution which involves variant thermal physical properties, phase transformation, sub-cooling boiling boundary and the effect of magnetic field. Using the finite different, the problem about non-linear heat transfer was linearized. At the same time, considering the change of boundary condition with time, a unified finited element fundamental equation was set up. Using finite element method to simulate the quenching process by additional magnetic field of 45 steel, the distributing of transient temperature on the condition of coupling effects of heat and magnetism is obtained.In the calculation of phase transformation, the continuous transformation curve and the isotherm transformation curve were taken together. Taking advantage of the continuous transformation curve, the beginning or the end or the time of transformation of a certain transformation was determined. Then the quantity of the continuous phase transformation was obtained according to the formula of the isotherm transformation.Through the calculation, we make out that additional magnetic field reduces the sample's cooling velocity and minishes the rate of temperature change. By additional magnetic field, the veloity which austenite change to martensite was acelerated and the content of residuary austenite was disminished. In the course of experiments, we measure the transient temperature fields and compare the results of measurement with that of calculation. By measuring the hardness, it is showed that after magnetic field quenching, the hardness of sample is slightly increased.Through the results and analysis, we can discover that utilizing heat transfer theory and computer technology to simulate magnetic field quenching process is feasible. The corresponding result is fit to practicality measureing value. It proves that the method used in this paper is correct by and large.