2015年, 第22卷, 第Supplement 1期　刊出日期：2015-11-25

  

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Abstracts
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  Process and Quality Control during High Speed Casting of Low Carbon Conventional Slab

  Lin-ping LI, Xin-hua WANG, Xiao-xuan DENG , Chen-xi JI

  中国钢铁期刊网. 2015, 22(Supplement 1): 1-9.

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  Based on the achievement of 2.5 m/min casting speed on Shougang Jingtang (SGJT) No. 3 slab caster, effect of casting speed on the parameters closely related to the casting conditions was discussed elaborately by plant trial, mathematical simulation and experimental study respectively. The results showed that mold level fluctuation, surface velocity, average heat flux, bulging of broad face, temperature of copper plate, solidification crater end and frictional force entirely increased while the powder consumption rate, subsurface inclusions and depth of hook structure decreased with the increase of casting speed. As a consequence, flow control mold (FC mold) was more significant to control the mold level than submerged entry nozzle (SEN) and powder B was more appropriate for high speed casting than powder A. And further, it is highly recommended that high speed casting should be considered as a potential application to improve the surface quality of cold coils.
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  Briquette Smelting in Electric Arc Furnace to Recycle Wastes from Stainless Steel Production

  Qi-xing YANG , An-jun XU , Peng XUE, Dong-feng HE , Jian-li LI , Bo BJ.RKMAN

  中国钢铁期刊网. 2015, 22(Supplement 1): 10-16.

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  Wastes from stainless steel production were briquetted together with carbon for smelt-reduction in the electric arc furnace, EAF, to achieve an internal recycling. A laboratory induction furnace was used to simulate the EAF. With a close simulation of the smelting, disintegration of the briquettes heated under load and recovery of metals from briquettes melted together with stainless steel and slag former were investigated. The influences of test conditions on carbon reduction of oxides in the briquettes were also examined. The briquettes endured heating at 1 186 °C under load of 3.5 kg and could be charged to the melt in small quantity without causing serious splashing. For a high metal recovery, it was necessary to charge the briquettes together with slag former. Small local zones of smelt-reduction with high carbon concentration could thus be formed during the charger heating. Silicon content in the metal near to the briquettes should be minimised to achieve a high degree of carbon reduction. Based on results obtained from this study, suggestions were made on smooth operations of smelt-reduction of the briquettes by using EAF or induction furnace with large scales.
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  Characteristics and Evolution of Inclusion Induced Surface Defects of Cold Rolled IF Sheet

  Hui-xiang YU, , Chen-xi JI, Bin CHEN, Chang WANG, Ying-hua ZHANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 17-23.

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  Cold rolled IF sheet has a high requirement for surface quality. Nowadays, more than half of surface defects in cold rolled sheet are caused by non-metallic inclusions generated in steelmaking and casting process. Three types of surface defects as sliver, peeling and hole were found in industrial samples. To investigate the evolution process of inclusion induced surface defects, hot rolling and cold rolling of industrial slab samples were carried out in pilot mill, then surface defects after cold rolling were analyzed with scanning electron microscope equipped with energy dispersive spectrometer (SEM-EDS). The results show that, the inclusions which create surface defects are mainly from deoxidation products and entrapped mold powder. Surface defects like pockmark, peeling, dent and scratch in cold rolled IF sheet are determined by position, size and property of the inclusions. Subcutaneous big size inclusions can lead to peeling and dent, while surface inclusion particles would lead to pockmark and scratch or sliver. To improve surface quality of cold rolled sheet, some measures should be adopted to further decrease and remove macro inclusions, and avoid hard inclusions to be bare to the slab surface.
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  Numerical Simulation of Gas-powder Flow in a Slot-plug Mixing Chamber

  Jian-an ZHOU, Kang WEI, Zhi-qiang LI , Zhong-qiu LIU , Xue-kai JIANG, Hong-wei NI

  中国钢铁期刊网. 2015, 22(Supplement 1): 24-29.

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  The slot plug is an important functional element for bottom-injection technology of powders and greatly influences the smooth operation of this technology. The mixing chamber is an important part of the slot plug, and its diffusion angle strongly affects the transmitting stability of powders. The two-fluid model and the two-phase k–ε turbulence model were used to describe the two-phase flow of CaC2 powders in a mixing chamber and to study how the angle of the conical section affects the pressure in the mixing chamber. In addition, the concentration and velocity distribution of the CaC2 powders were analyzed. The results show that, if the angle of the conical section is 45°, the gas-powder transmission pressure is stable, and the powder concentrates mainly around the central axis of the mixing chamber. If the angle of the conical section is 45° or 90°, the powder moves around the outlet and then passes smoothly through the slits.
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  Modelling of Bubble Aggregation, Breakage and Transport in Slab Continuous Casting Mold

  Lin-min LI, Zhong-qiu LIU, Bao-kuan LI

  中国钢铁期刊网. 2015, 22(Supplement 1): 30-35.

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  The bubble-liquid flow, especially the aggregation and breakage behavior, plays a significant role in the slab continuous casting process. A 1/4th water model was employed to investigate the two-phase flow characteristics and the bubble size distribution. A mathematical model based on the Euler-Euler approach was developed to analyze the bubble aggregation and breakage in the bubbly flow. The population balance model (PBM) was applied to calculate bubble size distribution, and the simulation was implemented through the MUSIG (multiple size group) model. The numerical predictions were verified by the water model experiment. The results show that the PBM is a useful approach for analyzing bubble size distribution and can be taken into industrial applications of gas-liquid two phase flow inside the continuous casting mold. The ratio of big bubbles and bubble mean diameter in the upper recirculation zone are found to decrease with the increment of water flow rate and increase with the increment of gas flow rate. The bubble aggregation and breakage behavior, bubble size distribution and the effect of gas bubbles on flow field in the continuous casting mold are revealed. The numerical results are compared with the experiment and they show good agreement.
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  Influence of Inclusions on Impact Properties of J55 Steel

  Hai-bo LI, Dong-wei ZHAO , Guo-sen ZHU, Chun-lin BAO , Jian YANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 36-41.

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  J55 steels are mainly used in the field of petroleum casing due to their excellent mechanical properties. Microstructure of J55 can improve its impact properties without losing strength. The characteristics of MnS inclusions including composition, morphology, size, mumber and area with different S content and Ca/S ratio in plates were studied utilizing SEM-EDS (scanning electron microscopy-energy dispersive spectrometry) and ASPEX. The effects of inclusions characteristics and molten steel compositions on impact properties were also investigated. The results demonstrate that inclusions affecting impact properties are mainly massive string typed MnS, especially those with size larger than 90 μm. Moreover, the number density and area density of MnS inclusions also have effect on the impact properties. The impact properties of steel are obviously improved by controlling S content to less than 0.004 0 mass% or Ca/S ratio more than 0.5 in plates, which ensures that the generation of larger size MnS inclusions is effectively inhibited and the number of MnS inclusions is reduced.
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  Controlling Transverse Cracks of Slab Based on Edge Control Technology

  Dong-feng HE, Sheng CHANG, Hong-bing WANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 42-47.

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  With the wide application of the micro alloy technology in recent years, the problem of slab surface transverse crack has become more severe. Based on the analysis of the J steelworks’ X80 steel slab transverse crack defects and the forming factors, the effect of slab edge control technology on transversal cracks was studied by numerical simulation. The results show that under the current wide-scope water spraying for 1 600 mm slab section size, the slab transverse temperature gradient was very high. Therefore, the temperature of the slab straightening segment could not avoid the third brittle zone completely, leading to frequent transverse cracks. To solve the problem, an optimization scheme of middle-scope water spray was proposed. After the optimization, the slab surface temperatures became more uniform, and the slab temperatures of the straightening segment increased than the third brittle zone, thus reducing the transverse cracks effectively. By changing the water spraying scope and cooling water volume, the edge control technology achieved the expected edge and corner temperatures, solved the problem of slab transverse cracks, and improved the slab quality.
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  Mathematical Simulation on Slag Entrainment in Bottom-blowing Gas Ladle with Immersed Cylinder

  De-hui ZHANG, Ming-gang SHEN, Chao WU, Qing-hua QI, Qing XU, Zhen-shan ZHANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 48-52.

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  A flow field mathematical model of the molten steel in a 150 t bottom blowing gas ladle has been established. The ladle blowing argon process was simulated by mixture multiphase model. The flow of the liquid steel and the phenomenon of slag entrainment on the surface of the liquid steel in bottom blowing gas ladle with immersed cylinder were studied. On the basis of the effects of the gas flow rate and the way of blowing on the flow state of the top slag and mixing of molten steel, the critical gas flow rate with the immersed cylinder was determined. The results show that the flow distribution of the liquid steel tends to be uniform, the liquid surface velocity decreases, the critical gas flow of slag entrainment increases and the mixing time is shortened in the ladle when an immersed cylinder is applied.
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  Continuous Casting of High-Al Steel in Shougang Jingtang Steel Works

  Chen-xi JI , Yang CUI, Zhi ZENG, Zhi-hong TIAN, Chang-liang ZHAO , Guo-sen ZHU

  中国钢铁期刊网. 2015, 22(Supplement 1): 53-56.

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  Reaction between mold flux and liquid high aluminum steel is considerably strong. It changes the physical property of the mold powder greatly and leads to a larger fluctuation of heat flux in the mold. Transverse depression and longitudinal cracks were often found on the slab surface. Three casting trials were carried out to investigate the effects of mold powder and slab width on castability and surface quality of high aluminum steels. The result shows that the SiO2 content of liquid mold powder decreases while Al2O3 content increases during the casting process. It was found that the degree of slag-metal reaction, addition and consumption of mold powder determined the final equilibrium content of SiO2 and Al2O3. Under the same process condition, it takes more time for the mold powder content to reach equilibrium when casting wide slabs than narrow ones. Considering the sticking and slab surface quality, mold powder A with high melting point and high viscosity is suitable for casting 1 200 mm-width slab and mold powder B with low melting point and low viscosity is suitable for casting 1 900 mm-width one.
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  Theoretical Study and Thermal Simulation of Titanium Removal in Combined Blown Converters

  Wei WU, Bing NI, Zhuang-zhuang LIU, Yong YANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 57-62.

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  Titanium removal in a basic oxygen furnace (BOF) converter process was simulated by an experiment in a 500-kg intermediate frequency induction furnace with top- and bottom-blowing functions, and the reaction mechanism of titanium oxidation was investigated. The results showed that the average end point mass percent of titanium in the hot metal was 0.008 2% and the rate of titanium removal was 71.3%. The rate of titanium removal decreased as the temperature of the hot metal increased, whereas it increased with the oxygen supply to the molten pool. The ratio between titanium and manganese is similar to that between titanium and silicon in the hot metal at the end point. However, the titanium content is not associated with carbon oxidation at the end point. The titanium distribution ratio between the slag and hot metal ranges from 0.6 to 1.6, and it increases with the (FeO) content in slag, but decreases as the temperature of the hot metal increases. The experimental results correspond with the theoretical analysis, which conclude that the titanium oxidation reaction is more likely to occur at lower temperatures.
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  Mathematical Simulation of Behavior of Carbon and Oxygen in RH Decarburization

  Peng-huan LI, Qiao-jun WU, Wen-hao HU, Jian-song YE

  中国钢铁期刊网. 2015, 22(Supplement 1): 63-67.

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  A mathematical model for RH decarburization was developed on the basis of the principle of carbon and oxygen balance. In the simulation, a physical description of the different reaction sites associated with the different mechanisms was considered. Furthermore, the oxygen transfer between top slag and molten steel was also considered. The calculated results of the model were in good agreement with the operation data of the two different plants. The model was applied to analyze the effect of KTB starting time on the RH decarburization rate for ultra-low carbon steel production using slag reforming or LF refining. According to the results, the RH decarburization rate especially the inner site decarburization rate is controlled by the KTB starting time. In actual operation, late KTB starting time should be avoided.
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  End Temperature Prediction of Molten Steel in RH Based on Case-based Reasoning with Optimized Case Base

  Kai FENG, , Dong-feng HE, , An-jun XU, , Hong-bing WANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 68-74.

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  Data redundancy issue of case-based reasoning (CBR) method can negatively influence calculation efficiency and prediction accuracy as the production data accumulate when predicting end temperature in Ruhrstahl Heraeus (RH) refining. A case base optimization method was proposed here to resolve the issue. The correlation between different cases in the original case base was analyzed by using similarity, and case base sets were designed in three different principles. Same testing data were used to examine all the cases in the case base set and the optimized case base was obtained via integrated comparison. Results from production data indicated that the case base set with minimum similarity provided optimal case base. Not only was the calculation efficiency enhanced, but the prediction accuracy improved. The research result has practical value to the application of CBR in RH refining in steelmaking industry.
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  Plasticity Steel for Automobiles

  Kang-wei LI , Chang-ling ZHUANG , Jian-hua LIU, Shao-bo SHEN , Yi-long JI, Zhi-biao HAN

  中国钢铁期刊网. 2015, 22(Supplement 1): 75-79.

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  The technologies for producing twinning induced plasticity (TWIP) blank in large scale with argon oxygen refining (AOD)-ingot casting-electroslag remelting (ESR) processes were studied. It was found that it was difficult to refine the low carbon Fe-25Mn-3Al-3Si TWIP steel using hot metal of high Mn content in AOD refining by a technology of decarburization and manganese retaining. However, it is practicable to perform decarburization and manganese retaining with the hot metal of lower Mn content in the early stage of AOD refining and do alloying with electrolytic manganese in the late stage. To overcome the problem of castability of TWIP steel, high superheat casting process was applied in ingot casting process, and the solidification structure of TWIP ingot was not compact and even, mainly composed of rough and long columnar and central random oriental dendrite. Due to the Ar protection and low current remelting processes applied in ESR procedure, the solidification structure was significantly improved and the inclusions were well controlled after ESR.
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  Optimization on Bottom Blowing System of a 210 t Converter

  Wen-jie WU , Hui-xiang YU, Xin-hua WANG, Hai-bo LI , Ke LIU

  中国钢铁期刊网. 2015, 22(Supplement 1): 80-86.

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  Bottom blowing has a significant influence on the stirring of molten steel in a combined blown converter. The effects of flow rate and configuration of bottom blowing tuyeres on the flow of molten steel inside the converter were studied with Eulerian multiphase model by using commercial software Fluent6.3, then the bottom blowing system was optimized based on the numerical simulation. The results show that the shape of the flow field of gas-steel phase zone is like an inverted cone, forming a strong center circulation and a weak circulation near the wall on both sides of the gas column because of bottom blowing. The average velocity of molten steel increases with the increase of bottom blowing flow rate. The flow pattern of molten steel changes little when the pitch circle diameter of bottom blowing tuyeres configuration changes. The molten steel has a good dynamic condition when the bottom blowing tuyeres are distributed at 0.55D (D is the diameter of the converter bottom) of the converter bottom. The simulation results were verified by industrial experiments.
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  Castability of Aluminum- and Sulfur-bearing Free-cutting Steel

  Yin-tao GUO, Qian WANG, Gu-jun CHEN, Sheng-ping HE

  中国钢铁期刊网. 2015, 22(Supplement 1): 87-92.

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  Submerged entry nozzle (SEN) blockage is one of the main problems during continuous casting of Al and S-containing steel, which has a negative effect on the smooth production and product quality. The blockage deposits mainly consisted of MgO·Al2O3 spinel, calcium sulfide, or (and) high-melting-point calcium aluminate. To understand completely the formation behavior of non-metallic inclusions and provide an optimization direction for improving castability, thermodynamic discussions on the generation characteristic of non-metallic inclusions before liquid steel flow through SEN were conducted. In addition, an industrial trial comprising of 10 heats made on five casting sequences was performed, including not only Al- and S-containing free-cutting steel, but also a medium-carbon Al-killed steel and a high-carbon Al-deoxidized steel. It was found that inclusions transferred into the MgO·Al2O3 spinel from pure Al2O3 and complex inclusions during vacuum degassing (VD) treatment. Two kinds of MgO·Al2O3 spinel inclusions were observed in the VD-treated steel. One is fine homogeneous inclusion of 1–2 μm in diameter, and the other is 10 μm-sized heterogeneous inclusions, which consisted of an Al2O3 core surrounded by a spinel coating. It was suggested that the former was generated from the mutual combination of fine MgO and Al2O3 particles produced from the erosion of the refractory materials during the VD process, and the latter was considered to be generated from the local reduction of large residual Al2O3 particles by soluble [Mg] provided by the decomposition of MgO in the ladle line during VD treatment. It was also discovered that CaS mainly results from steel-slag desulfurization during soft stirring.
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  Effect of Final EMS on Shrinkage Cavity of Bloom

  Qing-tao GUO, Ming-hong SHA , Ji-xiang JIA , Xiao-lei ZHU , Huan ZOU, Li-hua CAI

  中国钢铁期刊网. 2015, 22(Supplement 1): 93-97.

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  Final EMS parameters in the continuous bloom casting have been optimized by experimental and simulated researches. Simulation results show that the temperature gradient in the molten melt can be decreased and simultaneous solidification can be obtained with the final EMS. When the current is 600 A and frequency is 6 Hz, the maximum temperature gap between the inside and the brim of the melt bottom is 1.79 °C, which is 49.3% of that without EMS. Processing parameters are rectified based on the research results, the number of the shrinkage cavities is limited and the maximum diameter of the cavity is decreased.
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  Study and Application of Advanced Secondary Control Model for Continuous Casting at Baosteel

  An-gui HOU,, Qun-liang ZHANG , Guo-dong XU , Mao-fa JIANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 98-103.

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  A dynamic secondary cooling control model was developed to improve the quality of slab casting by combining the thermal transition computation method and proportional integral derivative (PID) controlling technology in continuous casting. The calculation principles, characteristics, and controlling parameters of the dynamic secondary cooling control model are described. The model automatically adjusts the secondary cooling flow according to slab casting parameters and maintains the slab surface temperature close to the target value. The reliability and usefulness of the secondary cooling control system are improved by quickly adjusting and stabilizing the secondary cooling flow. Online monitoring of temperature shows that the model is precise, and the surface cracks and central segregation were found to improve in the slabs. The model has been successfully applied to several continuous casters at Baosteel.
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  Effect of Deoxidation Process on Distribution Characteristics of Inclusions in Silicon Steel Slabs

  Zhen LI, , Cheng-jun LIU , Qun SUN , Mao-fa JIANG

  中国钢铁期刊网. 2015, 22(Supplement 1): 104-110.

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  The cleanness and usability of silicon steel are seriously affected by the type, number, size of the non-metallic inclusions. The evolution behaviors of the type, number, and size of inclusions in the non-oriented silicon steel slabs, which were subjected to different deoxidation processes (Si or Al deoxidation), were systematically investigated by using industrial testing and sampling analysis. The results indicate that the number and size of the inclusions are over larger during the starting-cast stage, and the reasonable cutting length for the first casting slab is 6 m. During steady-casting stage, the main types of the inclusions in Al deoxidization slab are Al2O3, Al2O3-MnS, Al2O3-MgO, Al2O3-AlN and their complex inclusions, and the main types of the inclusions in Si deoxidization slab are Al2O3, SiO2, Al2O3-SiO2 and a small amount of Al2O3-MnS, Al2O3-MgO complex inclusions. The number density and the occupation area fraction of inclusions in Al deoxidization slab are less than that in Si deoxidization slab. However, the stability of slab cleanliness in Al deoxidization process condition is inferior to that in Si deoxidization process condition.