Studies On Key Technology Of RH Refining Process During CSP Process To Produce DC04 Steel In JISCO

RH refining is an indispensable tache in the production of ultra low carbon. The effect of RH refining has direct relation with the quality of final product. To solve the key technological problems of RH refining process during CSP process to produce DC04 steel in JISCO, the flow field, decarburization process, the melting of Al block during deoxidation process and inclusion agglomeration and removal in molten steel in RH are investigated by numerical simulation in this paper. The main contents are listed as below:(1) The fluid flow in RH is of great significance to RH refining. After a deep analysis of the characteristics of the multiphase flow in RH, the inhomogeneous model which is available for Eulerian-Eulerian multiphase flow is established for the transient flow in a three-dimensional RH equipment. Based on this model, the flow pattern in ladle, snorkels and vacuum chamber is analyzed. The results show that the circulation flowrate will be enhanced by increasing the lifting gas flowrate and enlarging the snorkel diameter. The traditional definition of mixing time which identifies the local mixing time as the global mixing time for the bath takes a part for the whole. In regard to this, the concept of standard deviation is introduced and employed to redefine the time when the standard deviation of the tracer concentration in the bath equals 1 percent as the mixing time from the perspective of the global homogeneity of molten steel in RH. According to this new definition, the global mixing time is obtained. The results show that the global mixing time calculated by the new definition can represent the actual mixing in the bath much better than the local mixing time obtained by the traditional definition. During the simulation of mixing process of RH, it is suggested that the global mixing time should be calculated by this new definition. In experiment, rather than taking the maximum value or average value of the local mixing time, the mixing time should he obtained with the new definition by monitoring the variance of all the measured points. The more points, the better the result.(2) As the production pace of CSP process is very intensive, the efficient decarburization of RH refining is required to ensure the enough time for circulation and standing of molten steel during the deoxidation process. Combined with the operating parameters of RH refining in JISCO, a mathematical model for decarburization is developed. In this model, the vacuuming process and the continuous variations of vacuum pressure in vacuum chamber during this process are taken into consideration. Coupled with the fluid flow in RH, the variation of the content of carbon and oxygen are calculated and the spatial distribution of them is obtained. The model is validated by the results of exhaust analysis. The results show that enlarging the bottom area of vacuum chamber can be an effective way to raise the efficiency of decarburization. Taking the heat B214308393 as an example, the decarburization process is saved by approximately 7.5 min by expanding the radius of bottom surface of vacuum chamber from 0.8 m to 1.2 m.(3) During the RH refining process, the fluid flow in slag and slag-metal interface is stagnant and the slag shows a high oxidizability property. As a result, it is very difficult to decrease the slag oxidizability through the diffusion of deoxidizer. Subsequently, the oxygen in slag is transferred to the molten steel through slag-metal interface during casting process. To improve the deoxidation in RH slag and prevent the oxygen transfer from slag to the molten steel, a mathematical model for the motion and melting of Al block is established. The motion and heat transfer of Al block are coupled in this model. The melting route for Al block is analyzed and the relationship between the melting of Al block and the fluid flow, the original scale and initial temperature of Al block is investigated, providing fundamental basis for transporting the Al block to the slag metal interface.(4) In order to control the inclusion size distribution in molten steel, a mathematical model for inclusion agglomeration and removal in RH is established. A numerical method called "Cell Averaged technique" is introduced to solve PBE (Population Balance Equation). This method overcomes the shortcomings of the traditional PSG method on the prediction of inclusion size distribution. According to this method, the phenomenon that the submerged entrance nozzle can be clogged when less oxygen is blown during decarburization process in RH practice of JISCO is analyzed. The results show that the oxygen content after deoxidation is the most important factor which has an impressive influence on inclusion agglomeration and removal. It isn’t feasible when the value of the oxygen content after deoxidation is lower than 100 ppm. Otherwise, the inclusion agglomeration can’t be accomplished in a short time due to the small cardinal number of inclusions. As a result, the inclusion removal rate will be severely affected. The reasonable oxygen content after deoxidation should be approximately 300 ppm.