Fundamental Study On Molten Steel Transport Behavior In Continuous Casting Tundish With Arc Plasma Heating And Its Application

The core of the competition for high-quality special steel is the competition of key technologies.Nowadays,for high-quality special steel in China,the main problems faced by its production are unstable product quality,low degree of homogenization of products,differences in the composition of different parts of the product,and differences in the composition of different batches of products.Achieving constant temperature casting is an effective way to improve the homogenization of special steel products.The tundish heating technology can realize constant temperature casting of molten steel,improve continuous casting efficiency,improve the internal quality of the slab,and reduce the formation of central segregation and columnar crystals.Plasma heating creates the conditions for realizing the above advantages.Tundish plasma heating technology is currently a cutting-edge technology in the metallurgical industry.However,the development of tundish plasma heating technology has not yet formed a systematic system.Related researches are in urgent need of development.Based on this,this thesis studied the molten steel transport behavior in continuous casting tundish with arc plasma heating and its application.At the same time,this thesis was supported by the National Natural Science Foundation of China.An arc plasma model,an arc plasma heating molten steel model,and the tundish plasma heating and bottom-blowing argon synergistic model were established.The heating efficiency mathematical model of the tundish plasma heating system was established.And the metallurgical effect of the tundish plasma heating technology applied to the slab continuous casting tundish was analyzed.The following conclusions were obtained:The formation characteristics of DC arc plasma were analyzed based on the method of magnetohydrodynamics.Arc length and inlet velocity affect arc plasma formation and its temperature distribution.The temperature of arc plasma decreased along the axial direction and the radial temperature distribution was centered on the axis and gradually decreased along the radial direction of both sides.The temperature of arc plasma was distributed in a bell type.The axial velocity of arc plasma increased sharply at the cathode and then decreased gradually.The current density decreased exponentially along the axial direction.When the inlet velocity was 10 m/s,with the increase in arc length,the arc column was slender,and the effective area also increased.When the arc length was 20 mm or 25 mm,the jet phenomenon was the most obvious.Considering the effect of electrode material(graphite)on arc formation,a mathematical model of arc plasma heating molten steel was established.When the arc length was 10 mm,the effect of the inlet velocity on the heating of molten steel by the arc plasma was small.The highest value of molten steel temperature appeared in the axial direction of the arc,and the temperature of molten steel presented a trend of extending along the axial direction,and finally showed an elliptical temperature distribution trend.And there was a local high-temperature phenomenon.When the current value was 100 A,the radial temperature difference of the molten steel surface was small,and the temperature change was relatively stable.As the current value increased from 100 A to 150 A and 200 A,the molten steel surface temperature increased by 12.31%and 29.23%,respectively.Based on the income and expenditure terms of heat in the tundish plasma heating system,a mathematical model of heating efficiency was established.According to this model,the corresponding program code was established.The industrial testing data and the corresponding heating parameters were substituted into the heating efficiency calculation model.The model results were consistent with the range introduced in the literatures.It could provide effective theoretical support for adjusting the plasma heating parameters and dynamically feeding back the heating efficiency according to different industrial testing conditions at the site.A synergistic model of tundish plasma heating and bottom blowing argon was established.And the influence of plasma heating,and different argon blowing positions,heating time and heating power on the flow behaviors and heat transfer of molten steel in tundish with bottom blowing argon were analyzed.The results showed the molten steel temperature had been in a downward trend in the tundish without plasma heating.Plasma heating effectively improved the temperature drop of molten steel in the tundish during the casting process,but the accumulation in the high-temperature area caused by heating was serious.The simulation results at the B position of the argon blowing point(below the heating point)showed that the accumulation of high-temperature molten steel was basically eliminated,and the heating response time was shortened by 1.8%and 7.1%as the heating power increased from 500 kW to 750 kW and 1000 kW.The tundish plasma heating process was applied to the slab continuous casting tundish.The heating effect,the element content and the characteristic changes of the inclusions were systematically analyzed respectively.The temperature of the tundish fluctuated greatly during the casting process without plasma heating.For casting processes with plasma heating,the temperature could increase at a certain heating rate and reached the initial casting temperature state.Plasma heating had little effect on the content of carbon and nitrogen of molten steel in the tundish and slab.After plasma heating,the content of oxygen in the slab decreased to varying degrees.Plasma heating had no obvious effect on the inclusion type,but had a certain effect on the composition ratio.After plasma heating,the proportions of MnS inclusions and Al2O3-MnS composite inclusions in the slab samples decreased.At the same time,after plasma heating,the content of macro inclusions decreased to different degrees.