Steelmaking

Study and analysis on the CaO-Fe2O3-CaF2 dephosphorization agent of semi-steel

2018, 34(4): 1-7.

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This paper is based on a vanadium extraction converter to study the semi-steel dephosphorization process outside the furnace, in order to select a suitable dephosphorization agent for the semi-steel dephosphorization outside the furnace, so as to reduce the dephosphorization pressure of the converter and reduce the final phosphorus content to achieve ultra-low phosphorus steel production level. The vanadium-extracted semi-steel sample was tested in a laboratory tube furnace, and the most suitable amount of dephosphorizing agent for CaO-Fe2O3-CaF2 was 60 kg/t. Based on this, the proportion of the CaO-Fe2O3-CaF2 dephosphorizing agent was studied to obtain the optimal ratio: w(CaO)=30 %－45 %，w(Fe2O3)=40 %－55 %，w(CaF2)=10 %－15 %，and get the best dephosphorization rate of 79.1%. Finally, the dephosphorization process outside the semi-steel after field extraction of vanadium was designed and field tests were conducted to obtain an optimum dephosphorization rate of 61.4 %. Through the analysis of the optical basicity and phosphate capacity of dephosphorized slag, it is further verified that CaO-Fe2O3-CaF2 dephosphorization agent has a good dephosphorization effect, which provides a certain reference for production practice.

Application of skateboard type slag blocking technology in 240 t converter

2018, 34(4): 8-11.

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The technology of skateboard type slag blocking in converter was briefly described. Combined with the application of the 240 t converter slag blocking with slider system in Baotou Steel Rare-earth Steel Sheet Factory, the adaptability measures and actual results were introduced. The optimized process of skateboard type slag blocking effectively reduces the phenomenon of phosphorus reversion and the amount of slag in the tapping process, increases the yield of manganese and silicon alloy elements. The consumption of aluminum-iron alloy decreased by 0.39 kg/t and the consumption of ferrous charge decreased by 3.47 kg/t. The goal of optimizing steel quality and improving economic efficiency can be achieved.

Optimization and application of 100 t ladle refining slag system

2018, 34(4): 12-16.

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LF refining slag has an important role in LF refining process. Through the analysis of melting point，component activity，viscosity and sulfur distribution ratio, the refining slag of adsorbing inclusion ability and high desulphurization capacity had been designed. The main compositions of the refining slag were w(CaO)=55 %—59 %，w(Al2O3)=27 %—32 %，w(SiO2)=5 %—10 %，w(MgO)≤8 %，w(FeO+MnO)＜1 %. By material balance calculation, the slagging process had been devised and had been tested. The result showed that the composition of the slag can reach the target, and cleanliness of the product was obviously improved. The inclusion level of the product was all less than 1.0 grade, and the total oxygen mass fraction was between 0.0006 % and 0.0011 %，which was less than that of the old slag.

Study on control of height of the vortex during ladle final teeming by physical model

2018, 34(4): 17-23.

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For the problem of large residual steel caused by tall height of the vortex during teeming process of a 100 t ladle，based on the similarity criteria，a physical model with scale of 1︰3 was established, and water modeling experiments were carried out to investigate the influence of resting time, slag stopping balls and the argon blowing on starting and penetrating height of the vortex during ladle teeming. The results show that, when parameters of the ladle are given, both the starting and the penetrating height of the vortex first increase, and then decrease with increasing resting time. The use of a slag stopping balls, whose diameter is 60 mm and groove depth is 8 mm, could almost entirely eliminate the vortex and meet the requirement of the ladle steel flow. With the increase of argon flow, the vortex height decreases, and the starting and penetration height decrease by 58.8 % and 58.6 % respectively when the argon flow reaches 0.8 L/min.

Optimization of flow field in three flow asymmetrical tundish

2018, 34(4): 24-29.

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Taking the tundish of Zhejiang Qingshan Iron & Steel Co., Ltd. as the research object, the middle tundish is asymmetric three-flow, producing 200 mm×200 mm billets with a pulling speed of 0.95－1.5 m/min. The water model experiment was conducted in a 3︰5 ratio test, and mathematical simulation assisted observation was performed to observe the changes caused by the parameters of the retaining wall and the diversion hole on the flow field of the molten steel and the equalization of each flow to find the optimal design scheme. The experimental results show that the lag time of the right, middle and left water ports of the original tundish is 40 s, 17 s and 17 s respectively, the mean value is 24.7 s and the standard deviation is 13. The actual average residence time is 636.9 s, 519.4 s and 459.4 s respectively, the mean value is 490.8 s and the standard deviation is 90.28, the dead zone ratio is 23.9 %, and the consistency of the molten steel flow is poor. After the optimized U type retaining wall, the stagnation time of each nozzle is 33.8 s, 31.2 s and 29.7s respectively, the average value increases to 31.6 s, the standard deviation is reduced to 2.11, the actual residence time is 502.1 s, 532.7s and 517.1 s respectively, the average value increases to 517.3 s, the standard deviation is reduced to 15.3, and the flow consistency is greatly improved. The proportion of dead zone dropped to 19.8 %.

Analysis of CasterCrown technology principle of liquid core on-line inspection in continuous casting

2018, 34(4): 30-34.

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During the continuous casting process, accurately controlling the solidification process of slab, such as shell growth, surface temperature, shrinkage and solidification length, is the necessary condition to ensure slab quality, increase productivity and reduce production cost. The CasterCrown technology developed by EP Company is an on-line nondestructive testing of the solidification state of the continuous casting slab through mechanical scanning. The theoretical basis of CasterCrown detection technology was described in this paper. Based on the viscoelastic properties of solid-liquid coexistence zone in high temperature continuous casting slab, the constitutive equation of high temperature slab was deduced and the theoretical analysis of mechanical internal friction model was carried out. The mechanical properties of viscous internal friction in solidification region of the slab show that as the liquid fraction increases, the more obvious the anelasticity (strain falls behind the stress) and the larger the internal friction, and the internal friction can be characterized by the area of the stress-strain closed region. This paper introduces the system architecture and application of CasterCrown technology, which provides guidance and reference for the application of liquid core on-line inspection in continuous casting.

Experimental analysis of drainage sand behavior during conversion process during the change of ladle

2018, 34(4): 35-39.

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The flow behavior of the drained sand during the unsteady casting process was simulated by water model experiment, and the influence of the liquid level, the length of the long nozzle, the flowrate of lable, and the influence of the flow control device on the slag entrapment were studied respectively. The results show that the removal rate of sand was highest in the process of ladle changing when the optimum liquid surface height is 450 mm, and the optimum nozzle length is 180 mm,and the minimum lable flowrate is 6 m3/h. The reasonable flow control device can increase the removal rate of the drainage sand.

Investigation on surface quality of ML08Al cold heading steel continuous casting slab

2018, 34(4): 40-44.

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In order to solve the problems such as corner cracks, surface depressions and slag entrapment defects of cast billet during continuous casting of ML08Al cold heading steel produced by a steel mill in China, the theoretical analysis and field experiment methods were adopted. The results show that the surface quality of ML08Al cold heading steel continuous casting slab is related to multiple parameters of field production. By optimizing the water distribution in the secondary cold zone, the physicochemical properties of the mold flux, the composition of the steel, and the current mold electromagnetic stirring parameters can effectively reduce the surface defects of the ML08Al cold heading steel and its surface quality has been significantly improved.

Research and practice of increasing continuous casting heats for RH refining aluminum killed steel

2018, 34(4): 45-49.

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According to the actual situation of a steel mill, the process defect of Al killed steel smelting by RH refining furnace was introduced. Though the slag modification treatment of the molten steel after the converter，the oxidation property of steel slag was reduced, the fluidity of steel slag was improved and the adsorption capacity of the steel slag to inclusion was increased. The slag modification, decreasing adding aluminum amount and reinforced protective casting were adopted to reduce the content of inclusion in the molten steel sufficiently, improving the quality of the casting billet and obtaining good protective casting. After optimization, the continuous casting heats increased from 8 heats to 18 heats in a casting times, the purity of that molten steel was greatly improved and the grade of Al2O3 inclusion formation was reduced, so that the annual defect rate of rolling was reduced from 1.27 % to 0.49 % in 2017.

Reason analysis and solution on breakout warning in slab continuous casting

2018, 34(4): 50-54.

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In order to resolve the breakout warning in slab continuous casting of Guofeng Steel, Mould copper plate, mold flux, liquid level fluctuation of mold flux, stabilizing casting speed and replacing of the submerged entry nozzle were analyzed and optimized by the field survey analysis. By these measures, the average warning number of the two continuous casting machines was reduced to 8 times from 26 times per mouth, which greatly improved the production efficiency of casting machine.

Trial production of 10B33 cold heading wire rod

2018, 34(4): 55-58.

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The trial process of 10B33 cold heading steel wire rod in Handan Iron and Steel Co., Ltd was introduced. At the end of the smelting, a high catch carbon and re-blowing operation was adopted to reduce the oxygen content in the steel. During the refining process, the feeding timing of the aluminum wire was controlled to make the inclusions float up as early as possible. During the continuous casting process, the double-layer covering agent was used in tundish, and the tundish and immersed nozzle adopt integral type pouring to effectively control the secondary oxidation of molten steel. The quality of billet was improved effectively with the superheat of molten steel was controlled at 15～30 ℃ in tundish. During the rolling process, a controlled cooling process was used. The spinning temperature was between 880～890 ℃. The qualified 10B33 cold heading steel wire rods were successfully produced using the Morgan sixth generation reduction unit and the Steyr controlled cooling line.

Numerical simulation of shrinkage and sealing behavior during rolling of continuously cast slab

2018, 34(4): 59-65.

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In the production process of continuous casting slabs, there are often a large number of shrinkage holes inside the casting blanks. The spherical shrinkage pores are the most typical, shrinkage holes lead to internal defects, and the quality of the slabs is severely reduced. Therefore, the three-dimensional finite element model used in this paper was used to simulate the behavior of the shrinkage cavity during slab rolling, and the accuracy of the model simulation was verified by experiments. The results show that the three-dimensional finite element simulation results agree well with the experimental results, and the model can correctly predict the closing behavior of shrinkage pores during hot rolling. During the rolling process, the evolution characteristics of the spherical craters of different diameters are almost the same, and the closing process of the spherical craters with a large diameter is relatively fast; the farther the craters of the same diameter are away from the centerline of the thickness of the ties, the more distance from the surface of the cast slab. Nearly, the easier it is to close, the relative position in the rolling stock during closing of the shrinkage hole does not change.

Exploration on the properties of titanium inclusion in tire cord steel of different strength grades

2018, 34(4): 66-71.

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In order to achieve the effective control of titanium inclusion for the high strength tire cord steel，the properties of titanium inclusion in tire cord steel of different strength grades were explored by thermodynamic analysis combined with vacuum induction furnace experiment. The results are as follows: 1) The driving force of titanium inclusion precipitated in tire cord steel of different strength grades are different. The higher strength of the tire cord steel, the greater supersaturation of the titanium inclusion formed elements, thus the driving force of “nucleation-precipitation-grow up” becomes greater, and more helpful for the precipitation and grow up for titanium inclusion. 2) Titanium carbide and titanium nitride inclusions are existed simultaneously in the tire cord steel. The molar fraction of titanium carbide in titanium inclusion phase increased with the increasing of strength grade, and the color of titanium inclusions under the metallographic microscope are also changed. 3) The higher strength grade of tire cord steel, the larger average size of titanium inclusion precipitated during solidification, and the number of large titanium inclusions are also more. In order to effective control the precipitation of titanium inclusion in the super high strength grade tire cord steel, more strict measures of steelmaking and continuous casting process must be implemented.

The distribution of vanadium and phosphorus in modified steelmaking slag equilibrized with iron

2018, 34(4): 72-76.

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For the recovery of vanadium from V-bearing steelmaking slag，the paper focuses on the effect of binary basicity on the distribution of vanadium and phosphorus in steelmaking slag. The experimental results show that the basicity is greater than 1.8, phosphorus dissolved in dicalcium silicate, and vanadium occurs in dicalcium silicate and RO phases；basicity is between 1.3－1.5, most of phosphorus dissolved in the liquid phase, a small amount in the solid solution of orthosilicate, and vanadium concentrates in the spinel phase; when the basicity is 1, phosphorus exists in liquid phase, most of vanadium enriched in the spinel phase, a part dissolved in liquid phase.

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