2011年, 第18卷, 第8期　刊出日期：2011-08-15

  

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工艺
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  Investigation on Pulverized Coal Combustion Behavior by Non-Isothermic Integral Thermogravimetry Method

  QI Cheng-lin,ZHANG Jian-liang,LIN Xiang-hai,LIU Qin-yuan,WANG Xiao-liu

  中国钢铁期刊网. 2011, 18(8): 1-8.

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  The combustion process of pulverized coal was investigated by non-isothermic integral thermogravimetry. The thermogravimetry curves were fitted by the Coats-Redferm approximation function, and kinetic parameters and characteristic temperatures were obtained. The optimal mixing ratio and particle size can be ascertained. The characteristic temperature of pulverized coal can be obtained from the thermogravimetry curve, and the combustion of coal can be divided into homogeneous and heterogeneous combustion according to the differential thermal analysis curve. The activation energy of a single type of coal ranking from low to high is as follows: bituminous coal, meager-lean coal, and anthracite. In the first mixing method, with more low-price meager-lean coal B replacing high-price anthracite A, the activation energy slightly decreases; with more bituminous coal replacing meager-lean coal, total tendency makes a declining of activation. In the later mixing method, with an increase in particle size, a declining activation energy can be seen in total tendency.
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  Iron Extraction From Oolitic Iron Ore by a Deep Reduction Process

  LI Ke-qing,NI Wen,ZHU Ming,ZHENG Mei-juan,LI Yuan

  中国钢铁期刊网. 2011, 18(8): 9-13.

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  A laboratory experiment was carried out to extract iron from oolitic iron ore by a deep reduction and magnetic separation technique. The raw coal with fixed carbon of 66.54% was used as the reductant. The iron was successfully extracted from the oolitic iron ore which otherwise is nearly impossible to be separated due to its extremely fine-grain and mosaic nature. The results showed that an iron recovery rate of 90.78% and an iron content of 92.53% of iron concentrate could be obtained by such a technique. The optimized roast temperature is 1200 ℃ and time is 60 min. The subsequent magnetic separation was performed by using a magnetic field intensity of 111 kA·m-1 and a grinding fineness less than 45 μm of 96.19% for the sintered product.
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  High-Temperature Oxidation Behavior of Vanadium, Titanium-Bearing Magnetite Pellet

  HAN Gui-hong,JIANG Tao,ZHANG Yuan-bo,HUANG Yan-fang,LI Guang-hui

  中国钢铁期刊网. 2011, 18(8): 14-19.

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  By means of isothermal oxidation and chemical analysis, great importance was attached to the parameters that made effects on the oxidation degree of vanadium, titanium-bearing magnetite pellet in high-temperature processing (1073-1323 K). Based on the experimental data, oxidation kinetics of pellet was analyzed according to shrinking unreacted-core model subsequently. Experiment results display that the oxidation degree of pellet increases with increasing of oxidation time, oxidation temperature and oxygen content, as well as shrinking of pellet diameter. Under the condition of oxidation time 20 min, oxidation temperature 1223 K, oxygen content 15%, and pellet diameter 12 mm, oxidation degree of pellet reaches 92.92%. The analysis of oxidation kinetics indicates that oxidation process of pellet is controlled by chemical reaction with activation energy 68.64 kJ/mol at a relatively lower temperature (1073-1173 K). Oxidation process of pellet is mixed-controlled by chemistry reaction and diffusion with activation energy 39.66 kJ/mol in the temperature range of 1173-1273 K. When oxidation temperature is higher than 1273 K, the limited link of oxidation reaction is the diffusion control with the activation energy 20.85 kJ/mol. These results can serve as a reference to the production of vanadium, titanium-bearing magnetite pellet.
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  Low Temperature Reduction Degradation Characteristics of Sinter, Pellet and Lump Ore

  WU Sheng-li,LIU Xiao-qin,ZHOU Qi,XU Jian,LIU Cheng-song

  中国钢铁期刊网. 2011, 18(8): 20-24.

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  The reduction degradation characteristics of typical sinter, pellet and lump ore were tested with the reducing gas conditions simulating two kinds of iron-making processes. The results show that, in the same condition of gas composition and temperature, the reduction degradation degree (RDI＜3.15 mm) of sinter is high, RDI＜3.15 mm of lump ore is low and RDI＜3.15 mm of pellet is in the middle level. With two kinds of gas composition simulating different iron-making processes, the reduction degradation indices (RDI) of three kinds of iron ores all present the tendency of “inverted V-shape” in the temperature range from 450 to 650 ℃, and the RDI reach the maximum value at 550 ℃. The reduction degradation degrees of iron ores are extended when mixing the gas with hydrogen to increase the reduction potential, and the influence extent is discrepant for different iron ores. Colligating the increase amplitude of grains in small size fraction, the influence of reducing gas on lump ore is the greatest, the influence on sinter is the second, and the sensitivity of pellet on the reducing gas properties change is relatively small. As for the degradation form, lump ore and sinter both present the degradation of cracking, and the distribution of small grains generated from the cracking is in the range from 0.5 to 6.3 mm uniformly. The lump ore presents surface cracking, while sinter presents integral cracking. The pellet presents the degradation of surface stripping, and the proportion of grains smaller than 0.5 mm is the highest, which is up to 90% in the grains smaller than 3.15 mm.
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  BP Neural Network of Continuous Casting Technological Parameters and Secondary Dendrite Arm Spacing of Spring Steel

  JIANG Li-hong,WANG Ai-guo,TIAN Nai-yuan,ZHANG Wei-cun4,FAN Qiao-li4

  中国钢铁期刊网. 2011, 18(8): 25-29.

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  The continuous casting technological parameters have a great influence on the secondary dendrite arm spacing of the slab, which determines the segregation behavior of materials. Therefore, the identification of technological parameters of continuous casting process directly impacts the property of slab. The relationships between continuous casting technological parameters and cooling rate of slab for spring steel were built using BP neural network model, based on which, the relevant secondary dendrite arm spacing was calculated. The simulation calculation was also carried out using the industrial data. The simulation results show that compared with that of the traditional method, the absolute error of calculation result obtained with BP neural network model reduced from 0.015 to 0.0005, and the relative error reduced from 6.76% to 0.22%. BP neural network model had a more precise accuracy in the optimization of continuous casting technological parameters.
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  Numerical Simulation Analysis of Influence Factors to Shearing Force of Rolling Shear

  MA Li-feng,WANG Jian-mei,HUANG Qing-xue,SHUANG Yuan-hua

  中国钢铁期刊网. 2011, 18(8): 30-36.

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  The calculation results show that relative cut-in depth at the moment of maximum shearing force decreases with the increase of steel plate thickness; along with blade clearance increasing, shearing force would increase slightly compared with the slide pressure of blade carrier; shearing force increases significantly with the increasing blunt end radius; shearing force displays a bit decrement with the decreasing platen force, while the pressure on slide plate of blade carrier increases substantially; shearing force increases a bit with the increasing shear velocity and decreases when nip angle increases while the horizontal component force of shearing force along the direction of plate width increases rapidly. The above results have important reference and actual using value for studying calculation of mechanical parameters of rolling shear and its structural design.
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  Multi-Period Optimal Distribution Model of Energy Medium and Its Application

  ZHANG Qi,TI Wei,CAI Jiu-ju,DU Tao,WANG Ai-hua

  中国钢铁期刊网. 2011, 18(8): 37-41.

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  A mathematical model of optimal energy medium distribution in steelmaking process is formulated. In this model, three kinds of important energy mediums including byproduct gases, steam and electricity are considered, and the objective function accounts for both the change of generation and consumption of the byproduct gases and the demand of low (or middle) pressure steam and electricity for each period to maximize the benefit of products cost and minimize the consumption of energy. The results indicate that the optimal distribution scheme of byproduct gases, middle pressure steam, low pressure steam and electricity is achieved and case study shows that 6% of operation cost is reduced by using the proposed model comparing with the previous model.
材料
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  A Methodology to Predict Fatigue Life of Cast Iron:Uniform Material Law for Cast Iron

  Sinan Korkmaz

  中国钢铁期刊网. 2011, 18(8): 42-45.

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  Mechanical, physical and manufacturing properties of cast iron make it attractive for many fields of application, such as cranks and cylinder holds. As in design of all metals, fatigue life prediction is an intrinsic part of the design process of structural sections that are made of cast iron. A methodology to predict high-cycle fatigue life of cast iron is proposed. Stress amplitude-strain amplitude, strain amplitude-number of loading cycles relationships of cast iron are investigated. Also, fatigue life prediction in terms of Smith, Watson and Topper parameter is carried out using the proposed method. Results indicate that the analytical outcomes of the proposed methodology are in good accordance with the experimental data for the two studied types of cast iron: EN-GJS-400 and EN-GJS-600.
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  Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

  ZHENG Dong-sheng,ZHU Fu-xian,LI Yan-mei,CHEN Bing-zhang

  中国钢铁期刊网. 2011, 18(8): 46-52.

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  The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstructure containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ, Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37.2% and 28384 MPa·%, respectively) for the steel plate processed by cooling pattern Ⅲ.
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  A New Route for Identification of Precipitates on Austenite Grain Boundary in an Nb-V-Ti Microalloyed Steel

  SHA Qing-yun,HUANG Guo-jian,GUAN Ju,MA Xiao-jun,LI Da-hang

  中国钢铁期刊网. 2011, 18(8): 53-57.

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  The precipitates on austenite grain boundaries in an Nb-V-Ti microalloyed steel have been investigated by transmission electron microscope (TEM) examination of carbon extraction replica. The replica was prepared from specimen etched with saturated picric solution rather than Nital which is conventionally used. Then particles on both grain boundaries and triple point of grain boundaries were clearly observed and identified as (Nb,Ti)(C,N) particles. In case of conventional way, it is difficult to determine the location of particles with respect to austenite grain boundaries. The number of particles observed in new way developed was greatly reduced compared with that found in replica prepared by the conventional way, which may be caused by the dissolution of partial precipitates during the etching with longer time and at higher temperature involved in new way. Despite this, the new way developed provides an effective way to determine the precipitate particles on austenite grain boundaries.
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  Effect of Sulfur Content and Sulfide Shape on Fracture Ductility in Case Hardening Steel

  XIAO Guo-hua,DONG Han,WANG Mao-qiu,HUI Wei-jun

  中国钢铁期刊网. 2011, 18(8): 58-64.

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  The effects of sulfur content and calcium addition on smooth axisymmetric tensile fracture ductility of case hardening steel DIN 18CrNiMo7-6 have been investigated. The quantitative metallographic analysis of sulfide inclusions and the correlations between sulfide inclusions and fracture ductility were examined. Sulfide inclusions were found to have deleterious effect on fracture ductility, whereas the effect can be offset to some extent by calcium-treatment due to less easily deforming of sulfides during hot-working. The product (AA·λAW) of sulfide inclusion area fraction (AA) and its area-weighted aspect ratio (λAW) can be used as a parameter to describe the effect of sulfide inclusions on fracture true strain.
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  Effect of Heat Treatment on Microstructure, Mechanical Properties and Fracture Behaviour of Ship and Dual Phase Steels

  Fatih Hayat,Hüseyin Uzun

  中国钢铁期刊网. 2011, 18(8): 65-72.

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  Grade A (GA) and high strength steel DH36 ship steels possessing different chemical compositions were used, and strength properties of GA steel and DH36 steel were compared. Additionally, 4 types of dual phase (DP) steels with different martensite volume fractions (MVFs) were produced from GA steel by means of heat treatment and they were compared with other steels through conducting microstructure, microhardness, tensile and impact tests. The fracture surfaces of specimens (DH36, GA and DP steels) exposed to tensile and Charpy impact tests were investigated by scanning electron microscope. Furthermore, it was found that the specimens quenched from 800 and 900 ℃ had better strength than DH36 steel. The tensile test results indicated that the tensile strength of DP steel water quenched from 900 ℃ was 3 times that of GA steel and twice that of DH36 steel.
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  Mechanical Properties and Retained Austenite Transformation Mechanism of TRIP-Aided Polygonal Ferrite Matrix Seamless Steel Tube

  ZHANG Ming-ya,ZHU Fu-xian,ZHENG Dong-sheng

  中国钢铁期刊网. 2011, 18(8): 73-78.

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  Through the comparison of microstructure for polygonal ferrite (PF) matrix transformation induced plasticity (TRIP) seamless steel tube at different positions before and after tensile rupture, the transformation behavior of retained austenite (RA) was studied. The results showed that there were no yield points in tensile process and the splendid elongation and tensile strength were contributed by the uniform ferrite/bainite grains and the transformation of RA. The stability of RA was to some extent in inverse proportion with the ability of transformation induced plasticity. The coarse retained austenite located in ferrite and ferrite/bainite laths were all transformed into martensite during the tensile process.