2013年, 第20卷, 第2期　刊出日期：2013-02-15

  

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工艺
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  Reduction Kinetics of Vanadium Titano-Magnetite Carbon Composite Pellets Adding Catalysts Under High Temperature

  ZHANG Jian-liang,XING Xiang-dong,CAO Ming-ming,JIAO Ke-xin,WANG Chun-long,REN Shan

  中国钢铁期刊网. 2013, 20(2): 1-07.

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  Experiments were carried out by adding CaF2 and NaF as catalysts in an Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from 1473 to 1673 K. The scanning electron microscope (SEM) was used to characterize the microstructure of product. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39 kJ/mol without adding any catalysts. Adding CaF2 or NaF of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95 and 15.79 kJ/mol, respectively. In addition, temperature was an important factor influencing on reaction rate.
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  Reduction Behavior With CO Under Micro-Fluidized Bed Conditions

  LIN Yin-he,GUO Zhan-cheng,TANG Hui-qing

  中国钢铁期刊网. 2013, 20(2): 8-13.

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  To process optimization and improve the degree of reduction, a two-step experiment was designed. The experiment was carried out in the micro-fluidized bed. The reactor in the micro-fluidized bed is operated as a differential reactor to ensure an equal temperature and residence time with the reactor volume. The experiment used Brazilian iron ore and reducing gas of CO. The operating temperature was 400 to 800 ℃ and the residence time was between 10 and 60 min. In correspondence with experiment, microscopic technique was applied too. The test shows that temperature and residence time of the pre-reduction stage have an important effect on the degree of reduction. By using two-step experiment, the maximum value of reduction degree increases by 44.1% compared with the maximum value of traditional reduction experiment. Microscopic analysis shows that the specific surface area, surface morphology and texture of reduced iron ore after pre-reduction stage have an important effect on the degree of final reduction too.
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  Inclusion Composition Control During LF Refining for SPCC Using FactSage Combined With Industrial Trials

  CHENG Zi-jian,,GUO Jing,CHENG Shu-sen

  中国钢铁期刊网. 2013, 20(2): 14-20.

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  Steel plate cold common (SPCC) is a Al-killed steel with Ca-treatment. The control of Al2O3 inclusion into low melting point liquid region is beneficial for inclusion removal, cast-ability promotion and defects reduction during rolling. Thus it is essential to understand steel-inclusion equilibrium since inclusion composition is determined by composition of liquid steel directly through steel-inclusion reaction. Thermodynamic calculation software FactSage is performed to understand how to control inclusion composition during ladle furnace (LF) refining, and industrial trials are carried out to verify calculated results. Firstly, target region for controlling CaO-Al2O3-MgO ternary inclusion is analyzed on the basis of the ternary phase diagram and the relationship between activities related to pure solid and activities related to pure liquid was fixed by thermodynamic analysis in order to obtain reliable activities for components of inclusions in the target region by FactSage. In addition, inclusions in steel samples are detected by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). It is found that most of Al2O3 inclusions are modified into lower melting point region but a number of them are still located in high melting point region at the end of LF refining after Ca-treatment. Moreover, the composition of liquid steel equilibrating with liquid CaO-Al2O3-MgO inclusion is obtained by steel-inclusion equilibrium calculation when w［Al］s is approximating 0.03% as: a［O］ is 1.0×10-6 to 4.0×10-6, w［Ca］ is 20×10-6 to 50×10-6 and w［Mg］ is 0.1×10-6 to 3.0×10-6. At last, stability diagrams of various calcium aluminates and CaS are established and they show that liquid calcium aluminate inclusions form when w［Ca］ is more than 20×10-6, but CaS precipitation is difficult to prevent because sufficiently low w［S］ (＜0.003%) is required.
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  Effect of Basicity on Deoxidation Capability of Refining Slag

  DENG Zhi-yin,ZHU Miao-yong,ZHONG Bao-jun,DAI Yong-gang

  中国钢铁期刊网. 2013, 20(2): 21-26.

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  Mass action concentration (activity) calculation model was used to analyze the variation rule of mass action concentrations of slag compositions with basicity changing, and the effect of basicity on deoxidation capability and control of spinel and globular inclusions was investigated theoretically. From the calculation and experimental results, it was found that with the increase of basicity, the mass action concentration of Al2O3 and SiO2 decreases, while the mass action concentration of FeO and MgO increases at first and then decreases.Slag basicity below 3 to 4 would help to control spinel inclusions formation, and higher basicity improves formation of globular inclusions. Slag with basicity under 2 can effectively control the formation of globular inclusions. Deoxidation capability of slag increases with the increase of basicity, and slag with basicity about 4 could almost reach the maximum deoxidation capability. In order to smelt low oxygen steel with globular inclusions controlled, refining slag basicity should be controlled at about 4.
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  Multi-Objective Load Distribution Optimization for Hot Strip Mills

  JIA Shu-jin,,LI Wei-gang,,LIU Xiang-hua,DU Bin,

  中国钢铁期刊网. 2013, 20(2): 27-32.

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  Load distribution is a key technology in hot strip rolling process, which directly influences strip product quality. A multi-objective load distribution model, which takes into account the rolling force margin balance, roll wear ratio and strip shape control, is presented. To avoid the selection of weight coefficients encountered in single objective optimization, a multi-objective differential evolutionary algorithm, called MaximinDE, is proposed to solve this model. The experimental results based on practical production data indicate that MaximinDE can obtain a good pareto-optimal solution set, which consists of a series of alternative solutions to load distribution. Decision-makers can select a trade-off solution from the pareto-optimal solution set based on their experience or the importance of objectives. In comparison with the empirical load distribution solution, the trade-off solution can achieve a better performance, which demonstrates the effectiveness of the multi-objective load distribution optimization. Moreover, the conflicting relationship among different objectives can be also found, which is another advantage of multi-objective load distribution optimization.
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  Surface Temperature Change of U75V 60 kg/m HeavyRail During Heat Treatment

  KANG Hao,WU Di,ZHAO Xian-ming

  中国钢铁期刊网. 2013, 20(2): 33-37.

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  The U75V 60 kg/m heavy rail samples were heated to 900 ℃ in a resistance furnace for a fixed duration of 50 min. Under this condition, the samples were austenitized totally. Then, the samples were dragged out of furnace and cooled for 25 s in the open air. After that, the samples entered into the air spraying channel, and were cooled from the top and both sides by compressed air. During this period, main technical parameters were changed such as the distance between spray nozzles and surface of rail head, air pressure, air spraying time and air temperature. So under laboratory condition, optimal heat-treating parameters of U75V 60 kg/m heavy rail were determined as the distance between spray nozzles and surface of rail head of 15 mm, air pressure of 0.26 MPa, cooling time of 80 s, and air temperature of 28 ℃. The surface temperature at different positions of heavy rail was measured before and after heat treatment, and the temperature changing law was determined. The self tempering occurred on the surface of rail head after heat treatment, and the tempering temperature became the largest (about 3 min) after heat treatment, separately 528, 524 and 536 ℃ at the center, top fillet and bottom fillet of rail head. The heavy rail was cooled in open air after heat treatment; during this period, the temperature gap on the surface of heavy rail became smaller and smaller, and was reduced to zero when being cooled for 20 min.
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  Effect of Asynchronous Adjustments of Clamping Cylinders on Triangular Crack of Slab Castings Under Application of Soft Reduction

  LIU Ke,CHANG Yun-he,HAN Zhan-guang,ZHANG Jia-quan

  中国钢铁期刊网. 2013, 20(2): 38-47.

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  Soft reduction is known to be one of the best ways to improve the internal quality of slab castings such as center segregation, center porosity, centerline or triangular zone cracks, which is based on a proper adoption of the amount of reduction upon the given final solidification zone through roll gap adjustments. The synchronization of the clamping cylinders for roll gap adjustments should be very important to the application of soft reduction, including the synchronization of the clamping cylinders adjustments in the same and different segments. The synchronization of clamping cylinders adjustments is mainly affected by the adjustable accuracy of the four position-controlled clamping cylinders mounted in the upper frames of the segments according to a predetermined transformation relationship between the signals of displacement sensors and aimed roll gap, which, however, is also influenced by the installation accuracy, the precision of displacement sensors, the deformation of the segment frames and/or its bearing pedestals. Due to the actual asynchronous adjustments of the four clamping cylinders, the dynamic soft reduction operation is normally applied at non-ideal mechanical conditions. Here 7 possible situations of asynchronous adjustments of the local segments which may induce gap deviation have been presented. The roll gap deviation in the soft reduction region of a slab casting has been studied by a 3-D visco-elastic plastic FEM model, through which the additional inter-roll bulging, the related triangular cracks induced by one kind of the possible asynchronous adjustment situation and the effectiveness of soft reduction have been analyzed. A critical tolerance for the gap adjustments has been proposed for better contribution of soft reduction to the internal quality of slabs.
材料
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  Fatigue Property of Hot Rolled and Cold Rolled Strips

  LI Sheng-li,LI Na,PENG Xing-dong,LU Xiang-yu,LI Ji-guang

  中国钢铁期刊网. 2013, 20(2): 48-51.

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  Tension-tension fatigue properties of hot rolled and cold rolled strips with same contents and sizes were measured by using group test method at room temperature in air. The results showed that the fatigue properties of the hot rolled strips were obviously higher than those of the cold rolled strips. The hot rolled strips with similar or higher tensile strength exhibited superior fatigue property over the cold rolled strips. Fracture morphologies observed using scanning electronic microscope (SEM) showed that the hot rolled strips exhibited larger fracture areas, indicating a slightly lower plasticity, and more even fracture microstructure and stable properties. It is feasible and reliable to replace cold rolled strips with hot rolled strips.
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  Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters

  LUO Fang,,Lupoi Rocco,Cockburn Andrew,Sparkes Martin,O′neill William,YAO Jian-hua

  中国钢铁期刊网. 2013, 20(2): 52-57.

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  Stellite 6 powders were deposited on low carbon steel using SLD (supersonic laser deposition) under optimized parameters. The structure, line scan of elements and porosity of coating were examined and analyzed using SEM (scanning electron microscope), OM (optical microscope) and XRD (X-ray diffraction). The adhesion strength between coating and substrate was tested by PAT-ADHESION/TENSILE and E900STM adhesive. The results showed the deposition characteristics of optimized coating with N2 at a pressure of 3.0 MPa, a temperature of 450 ℃ and a laser power of 1.5 kW were compared with those of Stellite 6 coating deposited by the HVOF (high velocity oxygen fuel).
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  Thermodynamics and Magnetostriction of Fe-Co-B-Si-Nb-C Bulk Metallic Glasses

  GAO Zhen,NI Xiao-jun,GUO Jin-hua,LI De-ren,LU Zhi-chao,ZHOU Shao-xiong

  中国钢铁期刊网. 2013, 20(2): 58-61.

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  Fe-Co-B-Si-Nb-C glassy alloy with the addition of C was prepared by arc melting and copper suck-casting. The thermodynamics and soft magnetic properties were investigated. The casted amorphous alloys were heat-treated at different temperatures. The differential scanning calorimeter (DSC) results and thermal expansion show complete thermodynamics of crystallization. Its magnetostriction properties were studied by capacitance method. Saturation magnetostriction increases to 38×10-6. The amorphous alloy exhibits good soft magnetic properties with low coercivity and high saturation magnetic induction. The results show that minor addition of C is beneficial to enhance the saturation magnetostriction , and do not deteriorate the ability of forming amorphous.
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  Effect of Martensite Morphology on Impact Toughness of Ultra-High Strength 25CrMo48V Steel Seamless Tube Quenched at Different Temperatures

  ZHANG Chuan-you,WANG Qing-feng,,KONG Jin-li,XIE Guo-zhu, WANG Ming-zhi,ZHANG Fu-cheng,

  中国钢铁期刊网. 2013, 20(2): 62-67.

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  A 25CrMo48V steel for ultra-deep oil/gas well casings was quenched at 900-1200 ℃ and tempered at 650 ℃. The lath martensitic structures were characterized by optical microscope (OM), field emission scanning electron microscopy (FESEM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM), and the transverse impact energy at 0 ℃ was measured from the as-quenched and tempered specimens. The results show that with the quenching temperature decreased, the prior austenite grain, martensitic packet and block are refined, while the lath width seems to remain unchanged. The enhancement of impact toughness with the decreasing quenching temperature can be attributed to refinement of the martensitic structure with high-angle boundaries, and the block is the minimum structure unit controlling impact toughness. The transverse impact energy ［ECVN (0 ℃) ≥100 J］ required for seamless casings with ultra-high strength (Rp0.2≥932 MPa) has been finally achieved with the experimental steel quenched at 900-1000 ℃ and tempered at 650 ℃.
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  Warm Deformation of Low Carbon Steel Using Forward Extrusion-Equal Channel Angular Pressing Technique

  B Eghbali,M Shaban

  中国钢铁期刊网. 2013, 20(2): 68-71.

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  A combination of extrusion and equal channel angular pressing (ECAP) was used to deform a plain low carbon steel. This process consists of two successive deformations by extrusion and ECAP in a single die (Ex-ECAP). Cylindrical samples were heated to predefined temperatures (650 and 850 ℃) and then pressed through a die channel with crosshead speed of 10 mm/s. Microstructure and resultant mechanical properties of processed material were studied. The results showed that pressing temperature has a significant effect on the resultant microstructure. While at 650 ℃, the cold worked structure with elongated ferrite grains were obtained, and at 850 ℃ the microstructure consisted of elongated ferrite grains and very fine grains at their boundaries as a consequence of continuous dynamic recrystallization (CDRX) of ferrite phase. Also at 850 ℃, a particular microstructure consisted of cold worked ferrite and static recrystallized grains on shear bands was obtained.
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  Corrosion Resistance on High Strength Bainitic Steel and 09CuPCrNi After Wet-Dry Cyclic Conditions

  WANG Zhi-fen,YIN Fu-xing,WU Li-xin,SUN Yi-qiang,ZHANG Wan-lin

  中国钢铁期刊网. 2013, 20(2): 72-78.

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  The accelerated wet-dry cyclic corrosion tests have been carried out of a high strength bainitic steel and 09CuPCrNi. The results indicated that the corrosion resistance of 09CuPCrNi was better than that of the bainitic steel based on the mass loss measurements. The morphology and composition of the rusting products have been investigated in order to realize the mechanism of rust formation on the two steels. The rust scale on both steels was composed of a dense inner layer and a loose outer layer. The inner layer grew thicker and denser as the test proceeding. Both of inner and outer layers were mainly composed of magnetite (Fe3O4) and maghemite (γ-Fe2O3) with a small amount of lepidocrocite (γ-FeOOH) and akaganeite (β-FeOOH). The rust phase of γ-Fe2O3 was detected in a higher amount of the inner layer, resulting in a much denser inner layer. The inner rust layer of 09CuPCrNi being denser and thicker than that of the high strength bainitic steel was attributed to the alloying elements such as copper, chromium and phosphorus enriched in it. The protective inner rust layer plays an important role in the corrosion resistance of the steel.