Steelmaking

Numerical simulation and application of desulfurization lance with external spiral guiding groove

2022, 38(4): 1-6.

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Aiming at the poor kinetic conditions of hot metal desulfurization with granular magnesium injection by a lance with single straight nozzle and the difficulties in the implementation of mechanical lance rotation, a lance with external spiral guiding groove was proposed, and the injection process was numerically simulated. It is found that the lance with spiral guiding groove can effectively improve the stirring of hot metal and reduce splashing compared with the conventional one. The industrial test and application of hot metal desulfurization with granular magnesium injection in a 250 t hot metal ladle in a steel plant show that, the hot metal splashing and magnesium vapor combustion on the slag surface are significantly reduced. The unit consumption of desulfurizer is reduced by 6.0 % on average and the average service life of injection lance reaches 180 heats, which show its excellent application effect.

Study on oxygen consumption model based on data drive in a converter

2022, 38(4): 7-13.

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Models of oxygen consumption in a 45 t converter were set up based on actual production data with BP neural network, support vector regression machine (SVR) and LGBM(Light Gradient Boosting Machine) algorithms where their parameters were optimized with Bayesian optimization algorithm and the models′ features were selected by data preprocessing and mutual information methods. The actual production data of 1 176 heats were used to train these models, and the data of another 504 heats were used to verify the prediction results of the models. The results showed that the hit rate with LGBM model within ±50 m³, ±40 m³and ±30 m³ was 94.04 %, 85.91 % and 76.58 %, respectively. Compared with the support vector machine and BP neural network models, the LGBM model had higher prediction accuracy and stability and better generalization ability.

Prediction of Mn alloying yield in converter tapping process based on GA-BP neural network

2022, 38(4): 14-20.

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Deoxidization alloying is the last step of converter smelting process. The accuracy of alloy content control in molten steel directly affects the smelting difficulty and smelting cycle of refining process. The yield of alloy is an important reference standard for converter alloying workers. The accuracy of determining the yield of alloying elements directly affects the stability of molten steel composition and production cost. Through theoretical analysis and actual data verification，9 observable indicators that affecting manganese yield were selected. The data was then reduced by means of the factor analysis，and the 6 public factor matrices were obtained as the input of the model，the manganese yield was the output of the model，and the manganese
yield prediction model based on GA-BP neural network was established. The results show that the regression coefficient of the model R²= 0.714 78，the average error is 0.01. The number of more than 98 % of the predicted accuracy accounts for 75 % of the total，and the accuracy of the prediction is high，and the actual production has certain reference significance.

Lance optimization of 120 t converter and research on the jet characteristics in steelmaking environment

2022, 38(4): 21-27.

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Jet characteristic of oxygen lance directly affects the metallurgical performance of converter. To solve the problems of long blowing time and high oxygen consumption of a 120 t converter, oxygen lance nozzle optimization was carried out, then the jet characteristics was studied based on numerical simulation. In this paper, the features of high temperature and high CO concentration in steelmaking environment were fully considered, and the gas phase combustion mechanism was creatively introduced into the simulation. Firstly, the differences of temperature field and velocity field in the computational domain between the case without considering combustion and the case considering combustion were analyzed. The results show that combustion reaction between oxygen jet and CO will occur, and the combustion flame is mainly concentrated in the region between multiple jets. Gas phase combustion helps to suppress the attenuation of jet velocity and the coalescence of multiple jets. Simulation results of old lance and new lance indicate that the jet length and strand diameter of new oxygen lance are larger and have stronger impact ability. The new oxygen lance was applied at the steel plant, oxygen blowing time was shortened by 50 s, oxygen consumption was reduced by 1.37 m³/t, slagging was improved, lance sticking and slag slopping were decreased. Overall, the metallurgical indexes were improved comprehensively after applying the new lance.

Study and practice of BOF less-slag steelmaking technology with high-titanium hot metal

2022, 38(4): 28-35.

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The consumption quantity of slagging materials is one of key economic and technical indicators of BOF steelmaking and represents the technical level of steelmaking, but it is inconsistent with the requirements of dephosphorization and furnace-lining protection. In an iron and steel enterprise, the contents of titanium and phosphorus in hot metal are high due to titanium-bearing iron ore used for ironmaking in blast furnace, so the consumption quantity of slagging materials is high in order to meet requirements of dephosphorization and furnace-lining protection. Therefore, based on the characters of high-titanium hot metal and the characteristics of slagging in BOF, the rules about oxygen supply and slagging were improved, a method called as “magnesium fixing titanium” (TiO₂ becomes inactive due to its combining with MgO) was taken as a technique to suppress the disadvantage influence of high TiO₂ slag on dephosphorization and furnace-lining protection to enhance the advantage efficiency of slag. By the continuous improvement of the above processes, a BOF less-slag steelmaking technology with high-titanium hot metal was developed. The consumption quantity of slagging materials was reduced from 55.67 kg/t to 47.86 kg/t. Good economic benefit was achieved, and a foundation for the development of high efficient steelmaking technology was laid.

Study on dephosphorization behavior and mineralogical phase of converter slag by gasification

2022, 38(4): 40-46.

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For the cyclic enrichment of P element in converter slag, it is proposed to use reducing agent to remove part of P element in molten slag in the stage of slag splashing. At present, the dephosphorization rate of slag gasification in industrial tests has reached a level of close to 40 %. In order to further improve the dephosphorization rate of slag, the change law of P element in different phases in the process of slag dephosphorization was studied, and then the theoretical guidance and optimization direction for dephosphorization process operation were provided. The mineralogical phase before and after the reduction of converter slag were analyzed by SEMEDS and XRD. The results show that the P element of converter slag is mainly enriched in 2CaO·SiO₂ and 3CaO·SiO₂ phase displayed in granular and lath. The average distribution of P element in this micro region observed by electron microscope is 2.4 %. The gasification dephosphorization reaction is mainly carried out in these phosphorus rich phases, and the fracture of phosphorus rich phase becomes smaller after the reaction, the average mass fraction of P element in the micro area is 0.7 %. The content of P in CaO·Fe₂O₃ phase and RO phase of converter slag is low, and the average mass fraction is 1.1 % and 1.5 % respectively. After dephosphorization, the two phases are mixed, and the P mass fraction is reduced to 0.27 % on average.In order to further promote the dephosphorization reaction in phosphorus rich phase, dynamic conditions need to be improved.

Physical simulation study on optimization of bottom blowing process in RH refining ladle

2022, 38(4): 47-53.

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In order to improve the RH refining efficiency, the physical simulation research on the bottom blowing position and flow of RH refining ladle were carried out for the 120 t RH refining unit of a steel plant. Firstly, the more appropriate process parameters were determined, the lifting gas flow was 1 408 L/min and the depth of impregnation tube was 540 mm. Then, three different positions of bottom blowing holes were set relative to the positions of the riser and the down comer, which were that the single hole was directly below the riser, and the connecting line between the double hole and the riser and the downcomer was vertical and parallel. Through the study of three indexes of mixing time, circulating flow and flow velocity, it was found that the refining effect of the single hole was better than that of the double hole, the refining effect of double hole vertical position was better than that of parallel position, so it was recommended to adopt single hole bottom blowing process.

Study on the influence of refined slag on non-metallic inclusions in U75V steel

2022, 38(4): 54-62.

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The effects of basicity of refining slag and Al₂O₃ content on non-metallic inclusions in U75V steel were studied. The results showed that the basicity of refining slag had a great influence on the inclusions in steel. In the refining process of U75V steel, with the increase of basicity of refining slag from 1.4 to 2.0, the composition of inclusions in steel changed greatly. The average mass fraction of CaO increased from 43% to 62%, while the average mass fraction of SiO₂, MgO and Al₂O₃decreased from 37 %、16 % and 4 % to 8 %, 9 % and 2 % respectively. The basicity of refining slag had a great influence on the number density of inclusions in U75V steel. When the basicity was 1.4, the number density of inclusion was 2.95/mm². With the increase of basicity to 1.8, the number density of inclusion decreased to 1.42/mm², and the number density of inclusion began to increase. When the basicity of refining slag was 1.8, the number density of inclusion in steel was the lowest, and the refining slag was more conducive to the removal of inclusion. Al₂O₃ content in refining slag had an important effect on inclusions in steel. With the increase of Al₂O₃ content from 0 to 3%, the contents of CaO and SiO₂ in the inclusions decreased, while the contents of MgO and Al₂O₃ increased. The mass fraction of Al₂O₃ in the refining slag was increased to 6 %, and the mass fraction of CaO in the inclusion remained stable at about 40 %, while the content of MgO and SiO₂decreased slightly, and the mass fraction of Al₂O₃ increased to about 18 %. With the increase of Al₂O₃content in slag, the number density of inclusion in steel increased continuously, and when Al₂O₃mass fraction in slag increases from 3 % to 6 %, the number density of inclusion increased by nearly one time. Therefore, U75V needs to control the Al₂O₃mass fraction in refining slag below 3 %. In the process of production, Al_s and Al₂O₃content in alloy and slag-making materials should be strictly controlled, Al₂O₃content in slag should be reduced, and basicity of slag should be controlled at about 1.8.

Multiphase flow behavior in a continuous casting tundish during ladle change

2022, 38(4): 63-70.

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In order to improve the steel cleanliness during ladle change, the steel-slag-air flow behavior in the tundish was investigated using numerical simulation and physical modeling. The effect of the refilling time on the multiphase flow behavior in the tundish during ladle change was also studied. The results showed that for the refilling time of 97 s the reoxidation was always occurred in the tundish during ladle change. A massive amount of gas phase was sucked into the impact zone at the start of pouring from the new ladle and the exposed area fraction of slag phase at the top surface was rapidly increased. After 5 s, the amount of sucked gas and the exposed area fraction of slag phase remained relatively stable. Reasons for the slag exposure mainly included: 1) the slag layer near the ladle shroud was directly impinged by the liquid steel at the start of pouring from the new ladle; 2) the thickness of the slag layer became thinner due to the shear effect of liquid steel flow. Increasing the refilling time during ladle change decreased not only the kinetic energy of liquid steel acting on the slag phase near the ladle shroud, but the shear effect at the slag-steel interface. Therefore, the amount of sucked gas and the slag exposure in the impact zone were significantly decreased. To improve the steel cleanliness during ladle change, the refilling time in the tundish should be larger than 184 s.

Research on stopper rod corrosion mechanism and improvement for low-carbon and low-alloy steel

2022, 38(4): 71-77.

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In view of stopper rod abnormal erosion of SAE series low-carbon and low-alloy steel during casting process, stopper rod erosion mechanism and corresponding improvement measures were proposed through phase analysis and element distribution. The results show that the high carbon component in stopper rod reacts with the oxygen in molten steel to form a decarburized layer on the surface of stopper rod. The inclusions with high Si_O2 component in molten steel adhere to the surface of stopper rod, react with MgO, MgO·Al₂O₃, and form low melting point phase of Mg₂SiO₄ type, which is brought into molten steel under the action of molten steel, causing corrosion of stopper rod. The abnormal corrosion of stopper rod was significantly improved by selecting stopper rod with low carbon, high density and appropriate amount of SiC, increasing basicity of slag and reducing oxygen content in molten steel, and the number of tundish continuous casting furnaces increased from 8-10 furnaces to more than 15 furnaces.

Effect of magnesium treatment on inclusion of reinforced bar containing Ti

2022, 38(4): 78-83.

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The experiment of magnesium treatment of high strength rebars containing Ti was carried out by vertical resistance furnace in the laboratory. The changes of composition and size of inclusions of the samples before and after magnesium treatment were analyzed, and the formation and precipitation of inclusions were calculated using FactSage software. The results showed that the inclusions of the sample before Mg addition were Al₂O₃、TiN-Al₂O₃and TiN, and after Mg treatment, the inclusions were Al₂O₃、MgO·Al₂O₃、TiN-Al₂O₃、TiN-MgO·Al₂O₃and TiN. It was easy to form Al₂O₃in the steel with high oxygen content, on the contrary, the MgO was formed easily. And, It was difficult to form MgO inclusion in the steel containing higher Al content. TiN inclusion could be precipitated on the oxide or just precipitated during solidification of steel. The size of inclusion decreased after magnesium treatment. The MgTi₂O₄ inclusion was mainly formed under the condition of the steel with high Mg content and low temperature, and this kind of inclusion in the sample was mainly precipitated during solidification.

Research and practice of producing SK2 high carbon tool steel by CSP process

2022, 38(4): 84-88.

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Based on the characteristics of SK2 advanced high carbon tool steel, the production process of converter and refining to control the cleanliness of molten steel was analyzed, and the optimization direction of continuous casting mold flux, casting speed and specific water volume was studied. The process of high carbon and low phosphorus at the end of converter and oxygen and nitrogen control in refining process was designed. The continuous casting protective slag with low basicity, low melting point and good lubricity and the continuous casting process with secondary cooling specific water volume of 1.6-1.7 L/(kg·min) and drawing speed of 3.5-4.0 m/min were developed. The steelmaking process for producing SK2 steel was successfully developed in the thin slab continuous casting and rolling production line.

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