Fundamental Research On New Steelmaking Process Based On Full Scrap Arc Furnace

The full scrap steel making process has large fluctuations in P content,low C content,high viscosity of molten steel,and poor dynamic conditions due to furnace type limitations.The arc area is prone to nitrogen absorption,and the end point phosphorus and nitrogen content is generally controlled stably below 0.020%and 0.0060%.However,for steel with high processing performance,the phosphorus and nitrogen content in the steel is required to be not greater than 0.010%and 0.0025%,which is difficult to meet its composition requirements.In this paper,aiming at the problems of insufficient stirring power and difficulty in dephosphorization and denitrification in low-carbon molten pool,the slag system with low alkalinity and high phosphorus capacity,the slag formation route,and the CO2 nitrogen control process were studied;A "ternary" composite stirring process has been developed to compensate for insufficient stirring power in the molten pool.At the same time,the movement behavior and distribution of scrap steel in the molten pool under continuous feeding conditions have been analyzed,and a melting model has been established to improve the new full scrap steel arc furnace steelmaking processes such as pure flat molten pool scrap steel melting,gas-solid injection dephosphorization depth,and bottom blowing CO2 denitrification.Based on the thermodynamic calculation and combined with hot state experiments,a high phosphorus capacity slag system and slag formation route suitable for gas solid dephosphorization technology were studied.The results show that when the carbon content is less than 0.5%,phosphorus preferentially oxidizes to carbon;When the phosphorus content in the molten slag reaches 2%,the activity increases by 600 times,and phosphorus reversion occurs.At 1560℃,low basicity slag still has a high phosphorus content ratio,and proper addition of MnO and Al2O3 can reduce the viscosity of the slag;Using slagging route 3,low melting point compounds are formed at the initial stage of slagging,with high CaO solubility and low viscosity,which is conducive to rapid slagging.The thermodynamic conditions of molten pool in the whole process of electric arc furnace steelmaking were simulated by hot state experiments,and the nitrogen reaction law was studied.It is found that during the melting period of scrap steel,the nitrogen absorption reaction is a first-order reaction,and the mass transfer of nitrogen atoms in the liquid phase is the reaction limiting link.During the period of blowing oxygen and decarbonization,the denitrification reaction is a secondary reaction,which is controlled by the mixture of liquid phase mass transfer and interfacial reaction;In the early stage,the carbon content is high,and the amount of gas can be increased by bottom blowing CO2;If the carbon content decreases in the later stage,it should be switched to argon.At the heating stage,the oxygen content in the molten steel is high,which not only inhibits the interfacial reaction rate,but also reduces the mass transfer rate of nitrogen atoms.When CO or CO2 is used as the denitrogenation gas,part of the gas dissolves into the molten steel,so argon should be used as the denitrogenation gas.Based on the new smelting process,the material and energy balance calculation is carried out.The electric energy gap is increased from 23%to 64%(224.86 kWh)for the smelting of full scrap charge.The electric energy gap can be effectively compensated by increasing the carbon injection rate,CO secondary combustion rate,scrap preheating and reducing the air intake ratio.When low basicity slag system is used,the amount of lime is reduced by 29%;The nitrogen ratio can be controlled by adjusting the carbon powder injection amount,secondary combustion rate,air ratio and carbon dioxide injection ratio to prevent nitrogen absorption of molten steel during the melting period.A study on optimization of pool stirring with "three element" composite stirring was carried out.It was found that the "three element" composite stirring eliminated the dead zone,and strengthened the local circulation formed at the edge;The interface mass transfer is enhanced through multi-source flow field coupling,and the mass transfer coefficient varies exponentially with time.However,the requirements for stirring parameters for liquid steel mixing and steel slag mass transfer in the molten pool are not consistent,or even the opposite.Based on the similarity theory,the physical model of scrap movement behavior is established,and the continuous feeding scrap melting model is established.The results show that the movement behavior of heavy/light steel scrap is inconsistent,and the scrap is dispersed in the molten pool due to the combined action of impact,inertial sedimentation and liquid reflux separation mechanism.The addition position,shape,mixing mode and flow rate will affect the movement speed and distribution of light and thin scrap.Heavy steel scrap destroys the formation of bottom blowing stream,while light steel scrap will hinder the flow field movement;At the same time,the melting time model of scrap free pile is modified,and the scrap melting model under continuous feeding condition is established.