Numerical Simulation And Analysis Of Electroslag Remelting And Microstructure Of Cr20Ni80 Electrothermal Alloy

Electro-slag Remelting Casting is a kind of Near-Net Forming Technology, it combines refining with solidification, and makes the metallurgical and solidification quality of castings good. The temperature distribution and electric distribution of the slag pool as well as the temperature and depth of metallic molten pool have a great effect on the crystal structure and performance of the castings during the remelting process. With the development and widely using of this technique, the numerical simulation can be used for the study of thermal and electric field of the ESRC and has theoretical guiding significance to the feasibility of pratical production and the control of product quality.First, the mathematic model of thermoelectric was established, and made the electrode, slag pool, slag shell, casting and crystallizer as computational physical model. The simulation of temperature and electric field distribution of the remelting system were studied by the thermoelectric coupling element-SOLID69of ANSYS software using Langrange interpolation function, and the effect of current, cooling intensity and slag pool depth on the temperature distribution and depth of metallic pool was studied. Meanwhile, based on the Cellular automata model, Heterogeneous nucleation model and dynamic model of dendrite tip growth were established, and the simulation of the microstructure of casting was studied. In the meantime, the effect of cooling intensity, shape nuclear density and supercooling degree on the microstructure of casting were researched. Finally, The metallographic experiment was conducted to verify the simulation results. The conclusion in this paper as follows:(1) In the whole temperature field distribution of remelting system, hightemperature part is mainly concentrated in slag pool, under the salg-metal interface, the temperature reduces gradually, and the low temperature part formed; The temperature gradient and heat flow density is bigger near the electrode, crystallizer and the slag-metal interface, but the ones inside the ingot casting and slag pool are smaller; The potential distributes as layers, the potential mainly concentrates in the slag pool and the current density is very big, especially in the end of electrode, the potential and current density is the biggest; Below the end of electrode, the potential reduces gradually, and the one in slag-metal interface is zero.(2) The temperature field distribution of slag pool is like a prototype; All of the temperature, potential and current density near the end of electrode are the highest, the highest potential is40V, and the highest temperature is near2005℃;In the radial and axial directions of slag pool, the potential and current density reduce gradually as well as the temperature; The temperature gradient and heat flow density is bigger near the electrode, crystallizer and the slag-metal interface, but the ones inside slag pool is smaller.(3) Blow the slag-metal interface, the temperature distribution is like a parabolic shape, the temperature in the center of the interface is the highest, the depth of metallic pool is bigger, and the superheat degree of molten metal is higher;In the radial and axial directions of molten pool, the temperature reduces gradually, and temperature gradient and heat flow density near the contact area between the interface and crystallizer is bigger, but smaller inside the metallic pool; The potential and current density of metallic pool and ingot casting is very small, and the value of potential is basically zero.(4) All of the remelting current, cooling condition and the depth of slag pool have a great effect on the depth of metallic molten pool. As the increase of current, the highest potentcial and the highest temperature of the slag pool increase, in addition to the depth of molten pool; As the decrease of the cooling coefficient, the temperature and potential of the slag pool remain unchanged, but the average temperature below the slag pool increases gradually, and the the depth of molten pool also deepens; As the depth of slag pool reduces, it result in the decrease of the pole spacing, and the molten pool deepens.(5) Both of the cooling intensity and supercooling degree have a great effect on the microstructure of ingot casting. As the cooling degree increases from4℃to12℃, the proportion of equiaxial crystal of the casting microstructure decreases constantly, but the one of the columnar crystal increases constantly, as the cooling degree is4℃, the microstructure almost consists of small equiaxial crystals, and the microstructure is very uniform and pyknotic, whereas the microstructure is made up with all massive columnar crystals; As the heat transfer coefficient increase from1000W/(m2-K) to4000W/(m2-K), the proportion of equiaxial crystal of the casting microstructure decreases constantly, but the one of the columnar crystal increases constantly, besides, the grain size becomes rough as the increase of cooling intensity.(6) The solidification microstructure morphology of ingot casting can be predicted very well by the finite element simulation method, and the metallographic experiment results matches the simulation results very well.