Steelmaking

Basic research on recycling dephosphorization of converter slag after gasification dephosphorization

2020, 36(4): 1-5.

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In order to ensure the recycling effect of converter slag after gasification dephosphorization,the thermal experiment of gasification dephosphorization slag as feedstock for slag dephosphorization was carried out in the laboratory.The results showed that the gasification dephosphorization slag had the characteristics of high calcium oxide,high basicity,low P₂O₅ and high FeO.It could be directly used for secondary dephosphorization without going through the slagging process.When the dephosphorization of molten iron was carried out by gasification dephosphorization slag,the end point [P] content of molten iron increased with the increase of experimental temperature.The phosphorus mass fraction of the end point molten iron at 1 500 ℃ was only 0.067 %,and the corresponding dephosphorization rate was 40 %.Comparing the dephosphorization speed of the gasification dephosphorization slag and the preparation dephosphorization agent,it could be known that in the prereaction stage,the slag-forming rate of the gasification dephosphorization slag was fast,and the molten iron [P] content of the gasification dephosphorization slag was lower than that of the preparation dephosphorization agent.However,due to the phosphorus capacity,the end dephosphorization effect of the gasification dephosphorization slag was not as good as that of the dephosphorization agent.Therefore,it was recommended that the gasification dephosphorization slag can be used in combination with the newly formed slag agent in the industrial test to reduce the slag production while ensuring the dephosphorization effect.

Thermodynamics of the formation of non-metallic inclusions in the deoxidation process of tire cord steels

2020, 36(4): 6-11.

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Tire cord steel requires good drawing performance,and one of the main factors affecting its drawing performance is non-metallic inclusions in steel.The main source of non-metallic inclusions in steel is deoxidation reaction of molten steel.In order to control non-metallic inclusions in tire cord steel better,the deoxidation thermodynamics should be understood deeply.However,the already published deoxidation thermodynamics of pure iron cannot guide the industrial production practice,and the deoxidation thermodynamics of the molten steel of actual steel grades has not been systematized at present,which needs further study.In the current work,the deoxidation thermodynamics of tire cord steel was calculated and compared with that in pure iron.It was found that there are obvious differences between the deoxidization equilibrium curves under the composition of tire cord steel and that in pure iron.Since there are several alloy elements inevitably exist in the actual production process of tire cord steel,the deoxidization equilibrium curve under the composition of tire cord steel can more accurately guide the control of deoxidization and nonmetallic inclusions in the actual production process of tire cord steel than that under the condition of pure iron.

Thermodynamics and industrial practice of the formation of non-metallic inclusions during deoxidization of heavy rail steel

2020, 36(4): 12-18.

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In order to study the thermodynamics on deoxidization and the inclusion control of heavy rail steel,FactSage thermodynamic software was used,combining with the actual production,to analyze the complex deoxidization of U75V heavy rail steel and the formation of inclusions under corresponding conditions.The results show that in the production process of heavy rail steel,the dissolved oxygen content in steel decreased continuously with the deoxidization reaction and the movement of deoxidization equilibrium,and the composition of inclusions transformed from SiO₂-MnO to SiO₂-MnO-Al₂O₃ and CaO-SiO₂-Al₂O₃-MgO constantly,the final inclusion was composed of CaO-SiO₂-Al₂O₃-MgO.It was unreasonable to guide the actual production using the thermodynamics of pure iron since there was a large deviation between pure iron and commercial steel on the deoxidization thermodynamics,moreover,the deoxidization thermodynamics for actual molten steel was not yet systematic,and further research was needed.Inclusion controlling should also be considered during the deoxidization process,and it was necessary to ensure the deoxidization effect without affecting the removal efficiency of inclusions and preventing the formation of large size inclusions.

Study on nitrogen removal of CaO-SiO₂-Al₂O₃-TiO₂ slag

2020, 36(4): 19-24.

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The influence of the composition of CaO-SiO₂-Al₂O₃-TiO₂ slag on the slag denitrification ability at 1 600 ℃ was explored by the FactSage thermodynamic calculation software. The results show that the denitrification ability can be represented as individual elements TiO₂> SiO₂> Al₂O₃> CaO, under the condition of the same capacity of nitrogen, the basicity of slag increases with the increase of the content of TiO₂.The slag series with relatively good denitrification ability was analyzed when w(TiO₂) = 0,25%, 50%.The content of TiO₂ in CaO-SiO₂-Al₂O₃-TiO₂ slag can be adjusted according to the requirements of different steel grades for basicity of slag, so as to optimize the denitrification effect of slag. Compared with the actual data, the FactSage software was proved to be reliable in predicting the variation trend of nitrogen capacity of slag with different components.

Study on LF refining process of low carbon aluminum killed steel

2020, 36(4): 25-30.

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In order to optimize the LF refining process of low carbon Al-killed steel,the effects of LF light treatment,LF refining (without calcium treatment) and LF refining + calcium treatment on inclusions,product performance,cost and production process were investigated.The results show that the typical inclusions in hot coil samples with LF light treatment are aluminate + MnS composites,and the typical inclusions in hot coil samples with LF refining are aluminate + CaS composites.The oxygen content in hot coil samples are basically the same under different LF refining ways,and there is no significant difference in mechanical properties.LF light treatment leads to good cleanliness and low cost,but tends to cause stopper rising and nozzle clogging during continuous casting.It is concluded that LF refining (without calcium treatment) should be adopted in the production of low carbon Alkilled steel,and LF light treatment should be considered when the production is small or at the end of casting.

The vacuum decarburization process optimization study of high altitude RH refining equipment

2020, 36(4): 31-38.

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Thermodynamics and industrial practice of non-metallic inclusions of heavy rail steel during solidification and cooling

2020, 36(4): 39-47.

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U75V heavy rail steel was used in present work to investigated the transformation of inclusions during solidification and cooling of molten steel.Steel samples with varied chemical compositions were taken from blooms and molten steel of tundish,which was analyzed by the Aspex automatic scanning electron microscope,combined with thermodynamic calculation,the transformation mechanism of inclusions in the solidification and cooling process of heavy rail steel was obtained.The results show that inclusions in molten steel of tundish were mainly CaO-SiO₂-Al₂O₃-MgO type,which was uniform in chemical compositions.During solidification and cooling,not only the composition of inclusions changed,but also the heterogeneity of phase.The inclusions in blooms were CaO-SiO₂-Al₂O₃-MgO-CaS type with the content of CaO reduced in inclusions,while that of CaS increased,and the inclusions that showed a multiphase structure were mainly composed of phases such as CaS,MgO·Al₂O₃ and CaO-SiO₂-Al₂O₃-MgO,in which the MgO·Al₂O₃ phase located inside the CaO-SiO₂-Al₂O₃-MgO phase,and CaS wrapped outside.Thermodynamic calculation results are basically consistent with the experimental ones,and the difference in inclusion compositions may be attributed to the insufficient thermodynamic and kinetic conditions.

Research on numerical simulation optimization of special-shaped tundish

2020, 36(4): 48-53.

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The current study focuses on the flow and temperature filed for a special-shaped tundish applied in a steelmaking plant.The tundish were investigated with the help of numerical modelling to improve the flow and temperature field in tundish which assembles a turbulence inhibitor and several dams.The research results showed that the flow field in the prototype tundish are not favorable for temperature homogenuous,resulting in a large temperature differences between outflows.With the optimization of tundish,the dead zone volume is reduced to 7.52 % from 22.05 %,which is the dead zone volume from the prototype,demonstrating a significant improvement on the flow field，as well as the temperature distribution.In addition,the uniformity of flows were evaluated by calculating the standard deviation.The optimized tundish showed that an appropriate combination of inhibitor and dams makes homogeneous flow and temperature field in the tundish.

Study on the influence of cavity shape of the turbulence controller on the flow field of the four-flow long-pitch tundish

2020, 36(4): 54-59.

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Considering the four-flow long-pitch tundish of a certain steel mill，the effect of beam flow and the influence of the flow field in tundish of the far flow liquid steel update should be weighed when designing the shape of the inner cavity of the turbulence controller.The influence of different inner cavity shape of turbulence controller on the flow field in long-pitch tundish was explored with water model experiments and mathematical model experiment.This research demonstrated that，in terms of the balance beam effect and the renewal of the far flowing liquid steel, the quadrilateral turbulence controllers was more suitable for a particular four-flow long-pitch tundish than the circular annular and octagonal controllers.It is found that the law of beam strength was circular annular turbulence controller > octagonal turbulence controller > quadrilateral turbulence controller.In addition to the original beam function，the turbulence controller had the function of steel flow diversion.

Solidification microstructure simulation of C72DA high carbon steel billet

2020, 36(4): 60-64.

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In order to improve the internal quality of C72DA steel and reduce the center segregation of billet,the solidification structure of billet was simulated by ProCAST software,and the simulation results of solidification structure were compared with that of billet segregation.The results show that the variation of carbon segregation from billet surface to center is similar to that of average grain radius and maximum grain area obtained by simulation.It is concluded that carbon segregation can be improved by grain refinement.

Research on liquid steel breakout of intelligent prediction technology base on heat-force information fusion

2020, 36(4): 65-69.

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During the process of drawing steel through continuous casting machine,the characteristics of the billet shell and the temperature and friction between the billet shell and the mould was change when the billet shell was bonded,cracked and foreign body was involved in the leaking steel.An intelligent steel breakoutprediction system based on heat and force information fusion was established for thermocouple information sources,heat flux information sources,friction between mould and shell and friction information sources.The accuracy of breakout prediction system was increased from 71.43 % to 90.28 %.

Study on the effect of refining slag basicity on inclusions in spring steel

2020, 36(4): 70-74.

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In order to evaluate the influence of refining slag on inclusions in quantity,composition,size and morphology of spring steel,two different slag systems were designed to study the effect of slag basicity on total oxygen and inclusions by total oxygen analysis,slag sample analysis and inclusion analysis under EAF→LF→RH→CC process.The research shows that compared with low basicity slag (1.0),high basicity slag (1.7) has the advantage of deoxidization and desulfurization of molten steel,and the total oxygen is lower.The inclusions in steel are basically the same under different basicity conditions,which is mainly consist of MnS,CaO-SiO₂-Al₂O₃,Al₂O₃-MgO,CaS-MnS,TiS-MnS and other inclusions.The amount of MnS and CaO-SiO₂-Al₂O₃ inclusions in low basicity refining slag steel is significantly more than that in high basicity refining slag.The type A,B and D inclusions with high basicity slag are better controlled.Considering the inclusion control level,refining slag with basicity of 1.7 is more suitable.

Cause analysis and process optimization of longitudinal crack in medium carbon high manganese steel billet

2020, 36(4): 75-80.

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In view of the problem of the surface longitudinal cracks on the bloom of medium carbon high manganese steel,the crack morphology was observed by SEM,the composition of the crack micro area was analyzed by energy spectrum analyzer.The precipitation temperature of AlN and TiN was calculated by thermodynamic theory according to the steel composition,and the transformation of cooling process was simulated by Thermo-Calc soft ware to provide theoretical basis of analyzing the longitudinal crack of continuous casting bloom.During the optimization process,the liquid steel was titanium alloyed,and w(Ti)=0.040 % at the end of LF.The nitrogen mass fraction of molten steel reduced to 0.005 % ~ 0.008 % by vacuum treatment.The cooling water flow rate of wide and narrow sides of mould decreased from 850，700 L/min to 750，650 L/min,respectively.And the secondary cooling water volume changed from 0.20 L/kg to 0.17 L/kg.Through the above measures,the longitudinal crack of the continuous casting slab of medium carbon high manganese steel was eliminated.

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