| With the rapid development of manufacture industry in China, die, high pressure container, nuclear power and military industry are in great need of large slab ingot of high quality and large tonnage. Solidification structure and size of large slab ingots produced with ordinary method like mold casting and continuous casting are not satisfying. However, large slab ingots manufactured by electroslag remelting have a good solidification structure and section area size. Report on research of slab production using ESR method is rare, and further work has to be carried out to find out the relationship between technical parameters and product quality. The common casting process of composite roll can be classfied into liquid-liquid bonding method and liquid-solid bonding method, in which liquid-solid type casting has been paid more and more attention due to its independence of casting shape and its simple manufacturing process. The state of composite interface combination related to the performance of the composite roll directly, so analyzing the interface fusion conditions and researching the relationship between the process parameters of electroslag surfacing with liquid metal (ESS LM) process and temperature field, flow field, pool depth, the thickness of the molten layer has important significance to the development and consummate of the ESS LM process to produce composite roll.In this thesis, a mathematical model is built on the basis of electromagnetic equation, flow equation and heat transfer equation, and then commercial software ANSYS and CFX were used to solve this model, finally the distribution of electric field magnetic field, flow field and temperature field were obtained. Based on the above work, further research on effects of widening electrode, reducing radius of narrowside on narrowside surface wrinkle and relationship between ingot temperature field and different electrode distance, different slag height and different input voltage was conducted. Simulation results show that:(1)Voltage gradient, current density and joule heat power density are relatively high in the area between two electrodes in slag bath, which, on the contrary, are small in slag-metal interface. Moreover, magnetic flux density is high in the same area of slag bath. Electromagnetic force is large in and nearby slag bath between two electrodes, and the force points to both width sides of mould and slag-metal interface from the middle section of narrow side. Near the middle section of width side, molten slag moves from middle part to both width sides of mould, and in slag area near mould narrowside, molten slag move from, outside of each electrode to place between two electrodes.(2) By widening electrode, highest temperature of slag pool and ingot increase, which is enough for a good surface quality. By reducing radius of slab narrowside, the highest temperature of slag increases, however, the highest temperature of slab ingot does not increase. The temperature difference between central and corner part of slab narrowside decreases, and the temperature of slab corner part increases a lot.(3) When electrodes distance increase, the highest temperature of slag pool decrease, while temperature of whole slag pool becomes more even. Even though the highest temperature of slab ingot increases, the input power of slag pool doses not change, and thus metal pool depth does not change obviously. When slag depth decreases, the highest temperature of slag pool increases, and temperature of slag pool become more even, the highest temperature of slab ingot increases, too. At the same time, both metal pool depth and molten metal height increase a lot. Keeping input power of slag pool and electrode distance constant and increasing input voltage, the highest temperature of ingot and slag pool both increases, and so does the depth of metal pool.(4) The most optimal process parameters of bifilar mode electrode ESR furnace are as follow:electrode distance is70mm, depth of slag pool is200mm and input voltage is62V.According to the calculated temperature field, the indirect stress analysis was done and the displacement of casting in the mould was numerical simulated, and then surfaces shrinkage in the solidification process of width and narrow side in the slab can be obtained. Based on this, the inner chamber shape curve of width and narrow side of mould can be designed.Electrode temperature distribution was obtained through numerical simulation, and then the relationship of electrode temperature and height of electrode were matched. Through the thermogravimetric experiment, oxidation kinetics curves of12Cr2MolR steel and oxidation rate constant of different temperatures can be got. The oxidation rate and temperature were fitted, and the relationship between oxidation rate and temperature can be obtained, and then the relationship between oxidation rate and height of electrode was got. Through integration on time and height of electrode to the oxidation rate, oxidation weight gain of electrode made by12Cr2MolR steel in a certain period and insert speed can be got, and then the amount of FeO entering the slag pool was obtained during this period. According to the calculated results, for the bifilar electrode mode electroslag remelting process of electrode, the percentage of gaining weight of FeO in six minutes to the overall slag weight is0.2%when insert depth0.015m, remelting speed4.09×10-3m/s and overall slag weight600Kg.Take slag system when remelting12Cr2MolR as the research object, the deoxidation thermodynamics model was built. Aluminum was selected as deoxidizer, and then the equilibrium mass fractions of the slag-metal interface in the conditions of different aluminum additions was calculated according to the given mass fraction of each constituent of slag system and electrodes. According to the demand of the component Si, Mn, Al of12Cr2MolR steel, the allowed Al addition interval was obtained. The thermodynamic model built in this study was applied to WE690PT steel.Take the gas domain within the mold and enclosure above the slag pool as research object, the physical model was built. The flow field and concentration field in the electroslag furnace in different ventilation rate, injection angle and blowing flux were simulated with FLUENT software. Through visualization analysis of gas flow field and concentration field in the protection atmosphere enclosure of electroslag furnace in different technological conditions, reasonable technological parameter of protective gas injection were obtained: exhaust velocity of the exhaust port3m/s, spray angle of argon75°and jet flow of argon60m3/h.Composite rolls’ interfaces manufactured by liquid-solid bonding method were researched, and effect of pretreatment method of roll core, pouring temperature and preheating temperature of core to the bonding of interfaces were analyzed. The structures of interfaces were observed with metallographic microscope and SEM and line scanning to the element chromium was done with SEM. Effect of process parameters to the structure and element diffusion were researched; Shear stress experiment of interface was done to analyze the effect of process parameters to bond strength. The results show that treating the roll core with limewater, increasing the preheating temperature of roll core and increasing the pouring temperature of outer layer material are beneficial to the bonding condition and bond strength of composite interface. Through numerical simulation to the ESS LM process of present equipment, the most optimal technical parameters of ESS LM under laboratory conditions were obtained:voltage42V, withdraw speed10mm/min, pouring temperature1760K, and slag height54mm. |
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