Table of Content

05 June 2015, Volume 31 Issue 3

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Research of high catch carbon process of high carbon steel in converter smelting

2015, 31(3):  1-4. 

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Recarburizing after tapping in the ladle was widely applied to produce high carbon low phosphorus steel in Beiman Special Steel Co.,Ltd., and a lot of problems appeared in practice. Based on theoretical analysis and industrial experiments, the related technologies, such as slag formation, dephosphorization, the position of oxygen lance and end-point control, were optimized to reduce the effect of bad raw material. Such a high catch carbon technology was developed to produce high carbon steel in Beiman Special Steel Co.,Ltd. The industrial practice showed that the end-point carbon mass fraction rised from 0.12% to 0.29%, the consumption of deoxidizer decreased by averaged 0.21kg/t, the consumption of carburetant decreased by averaged 2.16kg/t, the cost per ton steel decreased by 30.76 yuan, and the rate of the eligible products rised by 3.5%.

Optimization of double slag process in BOF

2015, 31(3):  5-8. 

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The double slag process of BOF was optimized by balance calculation and research of dephosphorization law. Then the requirement of the tapping temperature was satisfied by raising the hot metal ratio from 84% to 88%. Moreover，results showed that w(MgO) of slag was best satisfy to 6%~8% with the basicity was 1.6~1.8 at the first deslagging and the final slag basicity was controlled at 3.5~ 4.0 , then the phosphorus mass fraction could be lower than 0.02% and the temperature of steel was higher than 1680℃ at BOF steelmaking end.

Application of aluminum killed steel casting residue in AOD furnace smelting process

2015, 31(3):  9-12. 

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The characteristics of AOD furnace smelting stainless steel process were introduced in the present paper, and the reasons of large consumption of smelting slag and reductant were expounded. In order to reduce the material consumption of AOD furnace，combining with high melting point and low alkalinity of aluminum killed steel casting residue, casting residue was used to AOD furnace smelting process of stainless steel through adiusting the smelting technology and industrial test. The results showed that the aluminum killed steel casting residue could replace part of lime in AOD furnace reduction period, which could effectively solve the problom of chromium oxidization caused by heat insufficient in AOD furnace smelting process. The best usage of casting residue was 20~30 kg/t through data analysis and contrast, which could reduce the lime 10~15 kg/t, ferrosilicon 4~6 kg/t, fluorite 3~5 kg/t, and cost of per ton steel about 35 Yuan. The process energy consumption has fallen dramatically.

Production of Al-killed low carbon and low silicon steel

2015, 31(3):  13-16. 

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Al-killed low carbon and low silicon steel has been produced by KR→BOF→CAS→RH→CCM process route. JNX06 steel satisfying the customer’s requirements could be produced by controlling sulfur content of molten iron in the converter, tapping and slag skimming, deoxidation alloying, CAS refining and slagging, RH vacuum, Ca treatment procedure, continous casting superheat control and stabilizing mould level. The mass fraction of silicon was controlled below 0.030%. The results under low power showed that the quality of casting was good, the level of center segregation of C-class was 1.0 and center porosity was 0.5.

Analysis and control of scar defects in thin slab continuous casting SPA-H steel

DONG Chang-zheng

2015, 31(3):  17-21. 

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Industrial optimization experiment on billet transverse corner of boron micro-alloyed steel

2015, 31(3):  22-26. 

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Typical cracks and microstructure were observed and analyzed by SEM, many precipitates were found along the grain which plays a significant role on the crack formation of boron micro-alloyed steels. High temperature mechanical properties of three boron micro-alloyed steels were tested by Gleeble-3800 thermal simulation testing machine and the actual slab temperature was measured in the continuous casting process. It shows that the external factors of transverse corner cracks is the deep oscillation mark and the straightening or bending process on low ductility temperature. According to the above research and analysis, the optimization scheme was concluded. The main optimization is adding titanium to nitrogen fixation after deoxidation by adding aluminum. The oscillation parameters was optimized as supplement. At last the crack rate of boron micro-alloyed steels was successful controlled from 10% to 1% .

Effect of roller EMS on slab quality and mechanical properties of linepipe plate

2015, 31(3):  27-30. 

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The slab internal quality and the mechanical properties of linepipe plate with and without in-strand roller type electromagnetic stirring (S-EMS) were studied. The results showed that the centerline segregation and center porosity of slab macroscopic structure were improved with the proper use of S-EMS. The central equiax crystal ratio was increased from 12% to 26%. The impact properties ( -20℃) and the drop weight tear（-15℃）were improved remarkably. The detrimental segregation bandings, coarse Widmannstatten and granular Bainite structures were greatly reduced. The ratio for KV2≥350J of rolled plate samples got to 100%, the qualified rate for the shear fracture area of drop weight tear test was increased 2.65%, and got to 100%.

Theoretical analysis and trial experiments on combined blown converter less slag dephosphorization steelmaking process

2015, 31(3):  31-35. 

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Thermodynamics and material balance analysis were adopted, based on which theoretical simulations were carried out, and the key point of the process was got. The low temperature and proper basicity of the dephosphorization stage was better for the phosphorus removal, and the higher the deslagging ratio was, the smaller quantity of lime was consumed, and the smaller the slag quantity generated. Results of the trial experiments showed that, the lime and dolomite quantity dropped by 25% and 36.67% respectively, and the average dephosphorization rate of 62.95% during the dephosphorization stage and 90.72% during the total process were got. By means of influencing factors analysis of dephosphorization rate, the control technology of dephosphorization stage was concluded that，the basicity of the slag was 1.8~2.0, the mass fraction of T.Fe was 16%~20%, and the temperature of the bath was 1400~1420℃. And the control technology of decarburization stage was concluded as, the basicity of the slag was 3.20~3.60, the mass fraction of T.Fe was 16%~20%, and the temperature of the bath was 1600~1640℃.

Effects of w(Ca)/ w(Al) on transformation of inclusions in the calcium treatment in 20Mn2 steel

2015, 31(3):  36-40. 

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w(Ca)/w(Al) is an essential parameter in assessment of calcium treatment and the amount of calcium fed into molten steel. FactSage software was employed to systematically study the factors including temperature, oxygen content and sulfur content which affect the process of calcium treatment, and the relevant effects were obtained. With different w(Ca)/w(Al) the precipitations of inclusions were analyzed in 20Mn2 steel, and it was shown that when the w(Ca)/w(Al) reached 0.10, liquefaction extent of inclusions was highest and temperature interval of liquid phase arrived at maximum value. In the case of w(Ca)/w(Al)=0.10, steel specimen was sampled and analyzed. It was indicated that inner compositions of inclusions were correlated with nucleation temperature and peripheries of inclusions were comprised of CaS formed during the cooling process. Meanwhile, number of inclusions declined and mean diameters of inclusions increased after calcium treatment.

Establishment of economic deoxidation platform technology for carbon steel

jimmy knancy

2015, 31(3):  41-44. 

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The traditional deoxidation mechanism of carbon steel was described in this paper, and the deoxidation costs of ferroaluminum and Si-Ca-Ba alloy were analysed and compared. In order to solve the problems such as too many inclusions forming using ferroaluminum deoxidation, bad oxygen removal effect using Si-Ca-Ba alloy deoxidation, and heavy submerged nozzle erosion problems, the deoxidization process of carburant and ferrosilicon was put forward, which could reduce the cost and improve the quality of molten steel. The deoxidation cost was reduced by 3.68 yuan/t, when the end point carbon mass fration was 0.04%~0.05%, the deoxidation cost was reduced by 3.33 yuan/t, when the end point carbon mass fration was 0.06%~0.10%. Meanwhile, the effective solution for rephosphorization and continuous castability which caused by the new technology was proposed.

Study and control of boron existing forms in boron-bearing steel

2015, 31(3):  45-49. 

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The crack rate of S355J-3-B steel slab produced by Nanjing Iron and Steel Co.，Ltd. was high in the production process. Based on the component of S355J-3-B steel, the existing forms of boron in steel S355J-3-B steel were investigated using the chemical analysis, raman spectrum and field-emission transmission electron microscope (TEM). The results of chemical analysis showed that when the total boron mass fraction was 15×10-6 and the acid soluble boron was 9×10-6 in S355J-3-B steel，BN precipitates were found using raman spectrum and TEM. The thermodynamic calculation indicated that aluminum should be added in liquid steel firstly for sufficient deoxidation in steelmaking; then titanium was added for nitrogen fixation; finally, boron was added into liquid steel. In the straightening stage of continuous casting process, the pinning effect caused by fine BN precipitates on austenite grain boundaries is the significant reason resulted in the occurrence of surface crack on the slab. However, it is favorable for improving the hot ductility of boron-bearing steel with titanium addition. The crack rate of S355J-3-B steel slab decreased from 10% to 3% with increasing the titanium content.

Mechanical properties prediction and chemical composition optimization of Q215B hot rolled strip

2015, 31(3):  50-53. 

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Through statistical analysis of chemical composition and mechanical properties of hot rolled strip Q215B, the regression model was established and the chemical composition was optimized. Practice production proved that the regression models was feasible to predict the performance, it reduced manganese alloy consumption and created the economic benefits of 12.22 RMB for per ton steel by the strength mode changed from carbon to manganese, realizes the low cost of steelmaking, the qualified rate of transverse cold bending increased nearly 30% with the new pretreatment process. Finally the low cost of steelmaking and the improvement of comprehensive properties were achieved.

Research on inclusions controlling for the high quality tube billet

2015, 31(3):  54-58. 

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In the consideration of problems in producing process, such as high oxidation of refining slag, the fluctuation of T.O content in molten steel and calcium yield rate, the inclusion control technology had been researched in the high quality tube steel. The refining slag and producing technology had been researched, the T.O content was reduced and stable. The calcium treatment technology had been confirmed based on the thermodynamic calculation and laboratory research. Industrial tests showed that T.O mass fraction was not more than 15×10-6, w（Cat）/w（Als）was not less than 0.07, w（Ca）/w（S）was not less than 1.9 when the research countermeasures were applied. The modification of inclusion was improved. Every type of inclusions was not more than 1.0 level and A+B+C+D was not more than 3.0 level. The inclusion control met the quality requirement of the steel.

Influence of titanium and zirconium comlex deoxidation on the inclusions and microstructure of steel

2015, 31(3):  59-62. 

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In this experiment，the titanium and zirconium were added to the steel，alone or composite addition. The morphology, composition and the size of inclusions was observed. The results showed that we could got a smaller size and a larger number of inclusion particles when titanium and zirconium were added. Inclusions mainly contained TixOy, Al2O3 and MnS when the titanium compound was added. And when added the zirconium, the inclusions mainly contained ZrxOy，SiO2，Al2O3，MnS. Added the titanium zirconium compound to steel could form the complex inclusions of ZrxOy, TixOy, SiO2, Al2O3, MnS. Tragranular acicular ferrite was formed when titanium zirconium compound added.

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2015, 31(3):  63-68. 

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For the high temperature thermodynamic properties, the differences between the casting steel and the rolled steel are very significant, and the differences between the different steel grades are also very obvious. In this research, based on the microscopic theory of solute segregation, and with the combination of the experimental test and calculation analyses, the high temperature thermodynamic properties of SS400 steel and 65Mn steel for casting condition had been researched. It is shown that, the equivalent thermal conductivity, the equivalent specific heat and the Poisson’s ratio are decided by the width of the corresponding solidification two-phase zone; the Young’s modulus of the casting steel could be fitted by the high temperature tensile test results; the coefficient of thermal expansion is decided by the liquid impenetrable temperature and the metal tissue types, for 65Mn steel, when solidifying, it forms γ-austenite directly, so its maximum coefficient of thermal expansion is bigger than SS400 steel, and reached 0.00036/℃.

Formation mechanism of slab corner transverse crack of the third generation automobile steel

2015, 31(3):  69-73. 

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In order to reveal formation mechanism of slab corner transverse crack of the third generation automobile steel, analogy analysis on the thermal expansion coefficient, thermoplasticity, phase change feature and the second phase precipitation behavior in the scope of the third brittle zone temperature had been carried out by using methods such as mathematical calculation, physical test, metallographic examination etc. The results show that precipitation of ferrite film and AlN on the austenitic grain boundary should be the internal reason for reducing steel high temperature ductility. Supercooling imposed on slab edge should be the external reason for promoting corner transverse crack. Besides, multiple phase change and precipitation of (Mn，Fe)3C in low temperature would increase the crack sensitivity of this steel at further. Based on this research, the controlling measures for corner transverse crack had been put forward and the whole process production for about 250t steel had been realized.

The application of the slag making and return-slag operation by limestone in converter

2015, 31(3):  74-78. 

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The technology of slag making and the return-slag operation by limestone was analyzed in this paper, which has been applied in Shijiazhuang Iron & Steel Co., Ltd., Hebei Iron and Steel Group and met the industrial requirements. The results showed that the technology could increase dephosphorizing rate, improve the quality of steel, and reduce smelting cost in converter steelmaking process. Contrast with conventional technology, the consumption of steel material of the new technology is dropped by 6 kg/t, slag is reduced by 25kg/t, the first hit-rate of temperature at steelmaking end-point is 11%, phosphorus content of endpoint is decreased by 0.003%, carbon content is increased by 0.06%, and the smelting cost is reduced by 19.7 yuan/t.