Steelmaking

Analysis on flow optimization & cost control in steel-making system

2013, 29(2): 1-5. doi:

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In this thesis,steel-making system flow is hackled,parsed and optimized in detail from process flow,time flow,material flow and information flow and by optimization of the steelmaking system flow the optimization of structure and improvement of functions of steelmaking as well as an optimal compromise between products,quality and cost have been realized.

Research and practice on converter process of slag reduction

2013, 29(2): 6-8,18. doi:

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Steelmaking process of decreasing converter slag is developed for Shasteel by exploring the suitable intermediate deslagging time and blowing parameters. The blowing process is divided into two stages, dephosphorization and decarburization and upon completion of the dephosphorization process certain amount of slag is poured out and then the steel is refined again for decarburization with small amount of slag. After tapping, a small amount of decarburization slag remains in the converter for dephosphorizing of the next heat. Steelmaking using this process could reduce production cost by decreasing lime and dolomite consumption and improve the stability of steel composition by increasing the efficiency of dephosphorization. Industrial test results show that converter lime consumption is reduced to 17 kg/t steel from 26 kg/t, and dolomite consumption reduced from 13 kg/t to 9 kg/t, at the same time,the mass fraction of phosphorus could be controlled within 0.0080 %~0.0182 %，with the average content of 0.0126 %,at the end of blowing.

Composition optimization of LF refining slag in high cleanliness Al-killed steel

2013, 29(2): 9-13. doi:

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According to Iso-activity lines of aCaO and aAl2O3,Iso-temperature lines and Iso-sulfur capacity line of the slag system of CaO-SiO2-Al2O3 obtained by Factsage software and KTH model, the impacts of LF refining slag basicity, ratio of w(CaO)/w(Al2O3), and mannesmann index on slag melting point, sulfur capacity and Al2O3 inclusions absorption are studied in this paper; furthermore, the ideal slag of highpurity aluminum killed steel is w(CaO)=50 %～55 %，w(Al2O3)=22 %～26 %，w(SiO2)=10 %～12 %，w(MgO)=5 %～8 %. The field test of 40Cr steel shows that the mass fraction of T.O and sulfur can be controlled in below 15×10-6 and 90×10-6 respectively and its cleanness reaches domestic advanced level.

Optimization and research on refining slag of large tube billet

2013, 29(2): 14-18. doi:

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The refining slag series of large tube blank is studied by methods of chemical analysis,lithofacies analysis,SEM and simulative calculation.The results show that the percentage of original slag higher than 1 440 ℃is 60 % of the total melting temperature.The high proportion of 2CaO·SiO2and 3CaO·SiO2 in the slag leads to the viscosity of refine slag above 2 P·s.After the optimization and application of new slag series,the mass fraction of average total oxygen is reduced by 5×10-6,the mass fraction of average nitrogen reduced by 15×10-6,and the mass fraction of average sulfur reduced by 60 %after VD refining in the steel.The mass fraction of lowest sulphur is controlled to 0.003 %.

Quality control and cause analysis on central segregation of round bloom

2013, 29(2): 19-21. doi:

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In casting two different sectional round bloom,namely Φ300 mm and Φ500 mm blooms simultaneously at a 5 strand round bloom caster in the Steelmaking Plant of Chengde Jianlong Special steel Co.,Ltd.,due to misalignment of the axis of coil of the electromagnetic stirrer with the centerline of the mold for small sectional round bloom,the greater the effect of segregation on the internal carbon segregation index of the bloom will be.By application of a series technological measures such as stable drawing speed,low overheat casting,optimization of slectromagnetic stirring and secondary cooling water distribution the carbon segregation index and equiaxel crystal macrostructure have been improved and they are completely up to the standard.

Causes and control research on the edge crack defect of hot-rolled strip Q235B

2013, 29(2): 22-24,7. doi:

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Inspection and analysis of the edge crack defect of hotrolled strip Q235B show that the main reason for the edge crack is mismatching of various processing parameters and supercooling of the slab corner at the juncture of the sudden fluctuation of casting speed in the process of fast changing the tundish.The transverse corner cracks taking place at the wave hollows of the oscillation marks further deteriorates and finally evolves into edge cracking defects.By adoption of the optimized continuous casting process the transverse corner cracks of the slab can be effectively reduced and the edge cracks of the hot rolled strip can be eliminated as well.In the meanwhile the edge crack defects can be avoided in rolling the trimmed slab by grinding the corner defect of the slab.

Application practice of refining ZG06Cr13Ni4Mo steel for hydroturbine purpose by 120 t VOD process

2013, 29(2): 25-29,3. doi:

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According to the thermodynamic and kinetic theory of “decarbonization and chromium conservation” under vacuum condition some research has been done on the practice of refining ZG06Cr13Ni4Mo steel in a foundry plant of Shanghai.The results show that the critical value of carbon and endpoint of oxidation in the process of blow refining in a 120 t VOD can be precisely judged by observing the variation curve of the oxygen differential pressure electric potential measured with a solid oxygen concentration difference cell as well as variation of offgas temperature and thus effective control of “decarbonization and chromium conservation” under the vacuum condition can be realized.

Analysis of factors affecting desulphurization efficiency of CaO based composite desulphurization agent

2013, 29(2): 30-33. doi:

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The present paper analyzes factors affecting the efficiency of desulphurization as well as the effects of lime quality, grain size of powder, charging amount, temperature and titanium content of the hot metal on desulphurization. The results of use in a specific steelmaking plant show that the desulphurizatin rate reaches 95.1 % and consumption of desulphurization powder is cut down to 13.5 kg/t from 17 kg/t as soon as w(CaO) takes up 90 % and powder with grain size less than 0.15 mm runs up to 96 % of the total hot metal.

Prediction of oxyen blow rate in BP neural network based converter refining

2013, 29(2): 34-37,4. doi:

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In light of the dynamic blowing process of converter a BP neural network based prediction model is proposed for the purpose of determination of total blow oxygen and end blow oxygen in converter steelmaking.Critical influence factors for total blow oxygen and end blow oxygen prediction can be determined by correlation analysis.Fivenumber summary method is used to discriminate the data.BP neural network is improved by LM algorithm.Then,several neural network models with different topology structure are trained and compared with the history data,and the best network topology is selected.The performance of the best neural network model is evaluated.The results show that the hit rate to total blow oxygen predicted by model is 87.88 % with control precision among 800 m3,and the hit rate to end blow oxygen predicted by model is 91.99 % with control precision among 400 m3 respectively.

LF end-point temperature prediction of molten steel by GMDH neural

2013, 29(2): 38-41. doi:

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In light of the complexity of influencing factors of LF smelting endpoint temperature, the temperature prediction of molten steel is carried out by GMDH (Group Method of Data Handling) neural network with the selforganizing data mining principle as the core. The hit rate of temperature between ±5 ℃is 78.31 %. The hit rate of temperature between ±7.5 ℃is 92.77 %. The material thermal effect model is established.Through calculation of thermal effects of different materials charging into the molten steel, all materials added to the LF refining furnace are translated into an input factor. The temperature prediction of molten steel based on GMDH neural network is improved. The hit rate of temperature between ±5 ℃ reaches 88.72 % and the hit rate of temperature between ±7.5 ℃ is 98.44 %. The hit rate of temperature prediction based on GMDH neural network using material model is significantly increased and the temperature prediction has better adaptability for the changes of material structure caused by the smelting multiple steel.

Prediction model of dissolved aluminum content in deoxidization process of RH refining

2013, 29(2): 42-44. doi:

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Based on productive performance of RH refining in Tangsteel,a predicting model of dissolved aluminum content in Al-killing stage has been constructed with multiple linear regression analysis.The results show that after decarbonization in RH the higher the dissolved oxygen content in the liquid steel the lower the dissolved aluminum in the liquid steel after deoxidation; properly high temperature of the liquid steel is favorable for increase of the dissolved aluminum content in the liquid steel; and with the increase of the aluminum addition into the liquid steel in hot metal deoxidation the dissolved aluminum in liquid steel grows up.The on-site measured value of the dissolved aluminum in liquid steel basically fluctuates around the predicted value.The model can successfully predict the dissolved aluminum in liquid steel after Alkilling in RH refining in Tangshan Steel Corporation of Hebei Iron & Steel Group and thus this newly developed model is credible.

Analysis mineralogical phases of mold flux film from Tangsteel

2013, 29(2): 45-48,5. doi:

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The mold flux film collected from No.1 CC machine of the Plate Mill of Hebei Iron & Steel Group for casting steel grades Q345B and Q235B is observed and
then the constituents of mineralogical phases of the film are analyzed by Xray diffraction and the microstructure of the slag film is observed by a polarizing
microscope and micro mineralogical phase of the film and the stratification structure of the glass phase are analyzed and the effects of the chemical compositions
of the mold flux on the formation of the mineralogical phase of the flux are checked and thus theoretical evidence is provided for development and application of
the CC mold flux.

Precipitation and ferrite nucleation stimulation of titanium containing inclusions in X120 pipeline steel

2013, 29(2): 49-52,7. doi:

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The precipitation conditions of titanium containing non-metallic inclusions in X120 pipeline steel are calculated with thermodynamics. In term of calculation of the target content of titanium in the pipeline steel X120 ( w(Ti)=0.015%), when w(Al)=0.000 35 %～0.003 30 % Al₂O₃·TiO₂ is formed and when w(Al)>0.003 30 % Al₂O₃ occurs and pure MgO inclusion can be formed only if w(Mg) ＞1.62×10¹³,and composite inclusions 2MgO·TiO₂ can be formed if w(Mg)=0.0008%. No pure MgO inclusions can be found in the X120 pipeline steel, in other word in the pipeline steel such a few deoxidation products as 2MgO·Ti₂O₃、MgO·A1₂O₃、SiO₂、A1₂0₃、Ti₂O₃、MnO may exist and they may mix with the sulphides to form the composite inclusions. The Results of observation by SEM are in coincidence with that of the thermodynamic calculation. The ferrite nucleation stimulated by Ti containing inclusions is observed by SEM and results show that Ti containing incusions in X120 pipeline steel possesses very strong ability to stimulate the nucleation of ferrite.

Analysis of the surface longitudinal crack of billet for 40Mn2 steel

2013, 29(2): 53-56. doi:

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Through macroscopic test, fracture analysis, tensile test, gas content measurement and other methods the present paper analyzes the cause of the surface longitudinal
crack of 40Mn2 steel bloom. The result shows that the grain boundary strength is lowered by the high content of hydrogen and increase of stress on the surface of
bloom arising from climate and other factors in the process of cooling leads to bloom crack along the coarse columnar crystals and then further expansion to
the longitudinal cracks.

Effect of dynamic soft reduction model on the improvement in inner quality of slab

2013, 29(2): 57-60. doi:

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n order to solve the problem of poor inner quality of the continuous casting slab with 250 mm×1 600 mm cross section produced in Nanyang Hanye Special Steel
Co.,Ltd., dynamic soft reduction control model is developed by the nail shooting test on the slab. After the model is put into the production of continuous casting slab, the parameters of dynamic secondary cooling and soft reduction can be adjusted according to different process conditions for different steel grades. The model can effectively reduce the center segregation in the slab and improve the inner quality of the slab. Therefore the conformity ratio of the rolled steel plates in ultrasonic detection test can be greatly upgraded by application of the model.

Experimental research on effect of continuous casting cooling intensity on composition segregation and band microstructure of rolled steel

2013, 29(2): 61-65. doi:

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The effect of different cooling intensities in the secondary cooling zone on the band structure has been studied and analyzed by rolling the test steel CJ20CrMnTi in 200 mm×200 mm under the different cooling intensities and then analyzing the segregation of the test piece and inspecting and comparing the band structure of the rolled products. The result shows that:the average center carbon segregation index of slab decreases to 1.065 from 1.08 with increase of water ratio in secondary
cooling zone, thus the composition segregation of the slab is effectively improved, the uniformity of structure of the rolled products raised and the control grade of the structure of the rolled products lowered to grade 1.5 below from grade 3.0 and the rolling efficiency is improved and the gas consumption reduced and the economic efficiency of the enterprise remarkably raised.

Study on final solidification point of continuous casting Q345 Steel wide slab

2013, 29(2): 66-70. doi:

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A solidification heat transfer mathematical model of wide slab is established based on practical production conditions of Q345 steel wide slab in Echeng Steelmaking plant to determine final solidification point. Besides, it is tested and modified by pinshooting technique. The results show that the relative error between the results measured by pinshooting technique and the results calculated by solidification heat transfer mathematical model is within 1.3 %, so the results calculated by solidification heat transfer mathematical model can reflect final solidification point of Q345 steel wide slab truthfully. In typical speed of 1.15 m/min, the mushy zone of 200 mm thickness wide slab is 13.32~20.95 m far from mold liquid level. In typical speed of 0.95 m/min, the mushy zone of 250 mm thickness wide slab is 16.16~23.45 m far from mold liquid level. In typical speed of 0.80 m/min, the mushy zone of 300 mm thickness wide slab is 19.34~27.65 m far from mold liquid level. The final solidification point is very different at different casting speed and slab thickness. After continuous casting process optimization the qualified percentage for central segregation in Q345 steel wide slab within rating I increases from 85.4 % to 99.5 %.

Research on cyclic utilization of converter steelmaking dust in BOF

2013, 29(2): 71-74. doi:

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Based on the mechanism of slagging and temperature controlling in BOF steelmaking process, raw materials, such as sludge, dust ash and binders, are processed into dust pellets to replace the aluminum slagging agents for slag melting in the early smelting stage and to substitute the iron ore for temperature adjustment in the middle and late stage. It is found that compared with aluminum slagging agents and ores, when dust pellets are recycled in BOF steelmaking process, dephosphorization rate can reach 80.7 % and increase by 4.9 %. In addition, foaming and flowing properties of slag are very good, and the basicity of slag and iron loss are
almost the same. Valuable resources, such as iron, can be recycled. At the same time, environmental pollution can be reduced, and steelmaking byproduct resources can be recycled in the steelmaking process.

Process and practice of “one ladle” technology

2013, 29(2): 75-78. doi:

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The present paper describes typical types and features of “One Ladle Supply Technology” in Steelmaking Shop. Meanwhile, it briefly introduces actual application of “One Ladle Supply Technology” in China and suggests general selection principles of “One Ladle Supply Technology”.

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