2013年, 第20卷, 第6期　刊出日期：2013-06-15

  

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工艺
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  Influence of O2 Content in Circulating Flue Gas on Iron Ore Sintering

  FAN Xiao-hui,YU Zhi-yuan,GAN Min,LI Wen-qi,JI Zhi-yun

  中国钢铁期刊网. 2013, 20(6): 1-6.

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  Circulating flue gas can reduce the emission of flue gas, and furthermore, it can reuse the waste heat effectively in the sintering process. Compared with conventional sintering, O2 that gets through the sintering bed decreases because of substituting circulating gas for air. The influences of O2 content on sintering process are studied through simulating the flue gas circulation sintering with artificial gas. It shows that, with the reducing of O2 content in circulating gas, the combustion speed of fuel decreases and incomplete combustion degree increases, which makes the flame front fall behind the heat front and reduces the heat utilization efficiency of fuel. The ultimate result is that the temperature of sintering bed decreases and the liquid phase reduces. In addition, the reducing atmosphere is strengthened because of flue gas circulation, which makes the magnetite increase yet calcium ferrite reduce gradually. Because the content of calcium ferrite with good strength reduces, the sinter yield and tumble strength decrease. To ensure the sinter index, the favorable O2 content of circulating flue gas is no less than 15%.
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  Melting Characteristics of Recycling Slag in Decarburization Converter and Its Application Effects

  WU Wei,MENG Hua-dong,LIU Liu

  中国钢铁期刊网. 2013, 20(6): 7-12.

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  The steel slag in the decarburization converter is treated by the little water-spreading (LWS) and the heat-stewed (HS) methods, which is used as the furnace burden of the dephosphorization converter. The slag characteristics by the LWS and the HS methods and its application effects as the furnace burden are researched. The results show the moisture content in the HS slag is higher than that of the LWS slag. There is higher total iron content in the HS and the LWS slags and almost same melting point. The dicalcium silicate content in the LWS slag is higher than that in the HS slag. The tricalcium silicate in the LWS slag is lower than that in the HS slag. There are a lot of calcium ferrite in the LWS and the HS slags, which is beneficial to dephosphorization and slag melting. The LWS and the HS slags are added to dephosphorization converter each charge by 3 or 6 t. The results show that the saving lime is 0. 7-1. 0 t for each charge. The petrographic constitute of final slag for the dephosphorization converter by adding the LWS and the HS slags is dicalcium silicate, RO phase and glass phase. There are a little calcium ferrite phase in the LWS slag, which is helpful to dephosphorization. So there are better dephosphorization effects for the LWS and HS slags.
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  Actuator Efficiency Adaptive Flatness Control Model and Its Application in 1250 mm Reversible Cold Strip Mill

  WANG Peng-fei,PENG Yan,LIU Hong-min,ZHANG Dian-hua,WANG Jun-sheng

  中国钢铁期刊网. 2013, 20(6): 13-20.

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  The existing research of the flatness control for strip cold rolling mainly focuses on the calculation of the optimum adjustment of individual flatness actuator in accordance with the flatness deviation, which is used for general flatness control. As the basis of flatness control system, the efficiencies of flatness actuators provide a quantitative description to the law of flatness control. Therefore, the determination of actuator efficiency factors is crucial in flatness control. The strategies of closed loop feedback flatness control and rolling force feed-forward control were established respectively based on actuator efficiency factors. For the purpose of obtaining accurate efficiency factors matrixes of flatness actuators, a self-learning model of actuator efficiency factors was established. The precision of actuator efficiency factors can be improved continuously by the input of correlative measured flatness data. Meanwhile, the self-learning model of actuator efficiency factors permits the application of this flatness control for all possible types of actuators and every stand type. The application results show that the self-learning model is capable of obtaining good flatness.
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  Effects of B2O3 and CaF2 on Melting Temperatures of CaO-SiO2-Fe2O3 System Fluxes

  WANG Hong-ming,YANG Li-li,LI Gui-rong,ZHU Xiang,ZHU Hua,,ZHAO Yu-tao

  中国钢铁期刊网. 2013, 20(6): 21-24.

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  Fluorite is widely employed as fluxing agent in metallurgy flux, which inevitably leads to serious fluorine pollution. B2O3 is employed as fluxing agent of CaO-SiO2-Fe2O3 steelmaking fluxes to substitute for CaF2. The effects of B2O3 and CaF2 on the melting properties of this system were investigated. The melting temperatures of fluxes including softening temperature (Ts), hemispherical temperature (Th), and flow temperature (Tf) were measured using the hemisphere method. The results indicate that the fluxing effect of B2O3 is more significant than that of CaF2. When the addition amount of B2O3 (mass percent) exceeds 6%, the melting temperatures of fluxes including Ts, Th and Tf are decreased lower than 1300 ℃. The basicity of fluxes has a significant effect on the melting temperature, and the melting temperatures of the fluxes increase with the increase of fluxes basicity. However, when B2O3 is used as fluxing agent, the melting temperature changes little with the basicity increasing from 2. 5 to 5. 0. These characteristics are suitable for steelmaking process. Moreover, Fe2O3 has an important fluxing effect on this CaO-based steelmaking fluxes. This indicates that the fluxes system is suitable for steelmaking process.
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  Improvement of Hole-Expansion Property for Medium Carbo Steels by Ultra Fast Cooling After Hot Strip Rolling

  WANG Bin,LIU Zhen-yu,ZHOU Xiao-guang,WANG Guo-dong

  中国钢铁期刊网. 2013, 20(6): 25-32.

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  The improvement of hole-expansion properties for medium carbon steels by ultra fast cooling (UFC) after hot strip rolling was investigated. It was found that finely dispersed spherical cementite could be formed after ultra fast cooling, coiling and annealing treatment. Tensile strength of the steel after annealing was measured to be about 440 MPa. During hole-expansion test, cracks were observed in the edge region around the punched hole because necking or cracking took place when tangential elongation exceeded the forming limit. Cracks were mainly formed by the coalescence of micro-voids. Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could increase elongation values of the tested sheets by suppressing the combination of the adjacent micro-voids, resulting in the improved hole-expansion property.
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  Burden Distribution Calculation of Bell-Less Top of Blast Furnace Based on Multi-Radar Data

  ZHU Qiao,,L Cheng-long,,YIN Yi-xin,,CHEN Xian-zhong,

  中国钢铁期刊网. 2013, 20(6): 33-37.

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  The burden distribution real-time estimation problem of multi-loop charging based on the real multi-radar data is resolved. Firstly, an iterative algorithm is introduced to calculate the radial coordinate of the pile-top. Then, based on the multi-radar data, the burden profile is estimated by a cubic-curve equation at the end of the multi-loop charging. Furthermore, the burden profile before the next multi-loop charging is calculated based on multi-radar data by considering the impact of burden descent. On the basis of these burden profiles, a more accurate thickness ratio of ore to coke (RO/C) at the radial direction of blast furnace can be obtained. Finally, an example is given to calculate the burden profiles and RO/C by using the real multi-radar data sampled from Baosteel, which shows the effectiveness of the method introduced.
材料
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  Effect of Niobium on Dynamic Recrystallization Behavior of 5%Ni Steel

  LEI Xiao-rong,DING Qing-feng,,CHEN Yuan-yuan,RUI Xiao-long,LI Shu-rui,WANG Qing-feng

  中国钢铁期刊网. 2013, 20(6): 38-44.

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  The single-pass hot compressions of two 5%Ni steels with and without niobium addition at different temperatures of 800-1150 ℃ and strain rates of 0. 01-1 s-1 were performed by using a Gleeble-3500 thermal simulator and the effect of niobium on the dynamic recrystallization (DRX) behavior was analyzed. The results showed that the niobium addition of 0. 04% can retard DRX in 5%Ni steel significantly by increasing the activation energy for DRX from 394 to 462 kJ/mol. The critical strain required for starting DRX in 5%Ni steel was increased by 0. 04-0. 10 with niobium addition when the steel was deformed at a strain rate of 0. 01 s-1 and temperatures varied from 950 to 1000 ℃. The critical temperature required for starting DRX in 5%Ni steel was also increased from 1000 to 1050 ℃ with niobium addition when the steel was deformed at a strain rate of 0. 1 s-1. Such a retarded DRX occurring in Nb-added 5%Ni steel can be attributed to the pinning effect of precipitates containing niobium.
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  Improvement of Impact Toughness and Creep Properties in Reduced Activation Ferritic Steels by Consumable Electrode Remelting

  KANG Wen-yi,ZHANG Chi,FAN Nian-qing,XIA Zhi-xin,,WANG Ping-huai,CHEN Ji-ming

  中国钢铁期刊网. 2013, 20(6): 45-51.

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  The effect of smelting processes on mechanical properties and microstructure of reduced activation ferritic steels was studied. Creep properties and impact toughness of reduced activation ferritic steels were obviously improved by vacuum induction melting followed by consumable electrode remelting process in comparison with the conventional vacuum induction melting process. The difference of impact toughness and creep properties between both steels mainly depended on the aspect ratio and mean size of precipitates. Decreasing the aspect ratio of carbides makes development of a shear band more difficult, which could increase impact energy and creep resistance.
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  Thermal Fatigue Behavior and Cracking Characteristics of High Si-Mo Nodular Cast Iron for Exhaust Manifolds

  YANG Yun-long,,CAO Zhan-yi,LIAN Zhen-song,YU Hai-xia

  中国钢铁期刊网. 2013, 20(6): 52-57.

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  The thermal fatigue cracking behavior of high Si-Mo nodular cast iron (NCI) is investigated by means of optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectroscope (EDS), in order to find a new material used in exhaust manifolds in First Automotive Works (FAW). Nodular cast irons with silicon content about 4. 7%, in combination with up to 1. 1% molybdenum, were produced by Jilin University and FAW. The repeated heating/cooling test was performed under cyclic heating at various maximum heating temperatures (Tmax) ranging from 800 to 900 ℃. Experimental results indicate that the thermal fatigue cracking resistance of high Si-Mo NCI decreases with increasing the maximum heating temperature. The periods for crack initiation are 24-36, 40-50 and 70-90 times associated with heating temperature of 900, 850 and 800 ℃, respectively, when the holding time is about 10 min at Tmax. When thermal fatigue cracking occurs, the cracking always initiates at the bigger surface of specimen. The major positions of cracks propagation are generally at the eutectic oxide boundary region and the region of the graphite disappearance. At the same time, the oxidation may accelerate crack initiation and propagation. On the other hand, micro-crack number varied from large to little because of shielding effect. As exhaust manifolds, the reasonable working temperature of high Si-Mo NCI is no more than 840 ℃ by test and analysis.
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  Microstructure and Mechanical Properties of Nodular Cast Iron Produced by Melted Metal Die Forging Process

  LI Nan,XING Shu-ming,BAO Pei-wei

  中国钢铁期刊网. 2013, 20(6): 58-62.

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  The microstructure and mechanical properties of nodular cast iron produced by the melted metal die forging process (MMDF for short) were experimentally researched. The main obtained results are: the nodular cast iron produced by this process can be machined as easy as traditional one only if holding at the remained temperature for 4 h; its strength and plasticity are obviously higher than those of traditional ones; the graphite size arrived at grade 8, and the graphite spheroidizing arrived at grade 1 or 2, but a streamline molded distribution of the graphite slightly appeared. Both of the strength and plasticity increased with the pressure when the pressure holding time was larger than its critical value. A new way to produce high properties nodular cast iron was provided.
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  δ/δ Grain Boundary Movement in Fe-0. 2%C-0. 8%Cr During Solidification Process

  YUE Xu-dong,LI Qing-chun,CHEN Shu-ying,CHANG Guo-wei

  中国钢铁期刊网. 2013, 20(6): 63-67.

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  The moving process of δ/δ grain boundary during the solidification process of Fe-0. 2%C-0. 8%Cr has been observed in-situ with confocal scanning laser microscope (CSLM), and the establishment of δ/δ grain boundary, the moving mode, the moving speed and the influence of correlative factor were explored in detail. The results showed that the clear grain cannot be formed when δ phase merged during solidification process of the steel if the actual cooling rate was 0. 045 ℃·s-1. The δ/δ grain boundary with shape of flat will be formed if there is no essential conjunction between δ phase in a long period of time. The movement of δ grain boundary cross point drives other δ/δ grain boundaries to move. The moving process is not stable, and the moving rate variation ranges from 0. 12 to 1. 65 μm ·s-1. Temperature of the system is the chief factor for influencing the moving rate of δ/δ grain boundary during the solidification. When the temperature fluctuation of system appears, the solidified grain boundary is re-melted, which results in the catastrophic fluctuation of moving rate for δ/δ grain boundary. When the solidification process reaches its end, the average moving rate of δ/δ grain boundary is quicker than that of L/δ interface. The coarsening rate of crystal grain in the melt is slower than that of solidified solid phase crystal grain.
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  Strain Hardening and Strain Rate Sensitivity Behaviors of Advanced High Strength Steels

  F Ozturk,A Polat,S Toros,R C Picu

  中国钢铁期刊网. 2013, 20(6): 68-74.

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  The mechanical properties of commercial dual phase (DP), transformation induced plasticity (TRIP), and high strength low alloy (HSLA-340) steel sheets are investigated and compared at various strain rates ranging from 0. 0017 to 0. 17 s-1 at ambient temperature. TRIP steel outperforms the other two materials, having comparable ductility and twice as large strength relative to DP steel. TRIP has larger strength and much larger ductility than HSLA-340. The exceuent ductility of TRIP800 is due to its high strain hardening capability, which promotes stable plastic deformation. It is observed that the strain hardening rate in TRIP800 does not decrease to zero at failure, as common in most materials in which failure is preceded by necking.
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  Effects of Rolling Parameters on Texture and Formability of High Strength Ultra-Low Carbon BH Steel

  CHEN Yin-li,SU Lan,ZHAO Ai-min,KUAI Zhen,LI Ben-hai,LIU Guang-ming

  中国钢铁期刊网. 2013, 20(6): 75-81.

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  The effects of hot rolling and cold rolling parameters on texture and r (plastic strain ratio) value of high strength ultra low carbon bake hardening (ULC-BH) steels are studied with orientation distribution function (ODF) structural analysis method. After hot rolling, the high strength ULC-BH steel sheet has weak γ-fiber with uniform orientation distributions, and weak α-fiber, of which {445}<110> component forms a high intensity peak at coiling temperature of 750 ℃. After cold rolling, both {111}<110>-{111}<112> intensity on the γ-fiber and {111}-{112}<110> intensity on the α-fiber enhanced. As a result of substitutional solute elements Mn and P being added to the steel, strong {112}<110> deformation texture component is observed on α-fiber, especially at 80% cold rolling reduction, and this leads to the strong {111}<112> recrystallization texture after annealing. The increase of cold rolling reduction shifts the maximum intensity on the γ-fiber from {111}<112> to {111}<113>. After annealing, a very strong γ-fiber is obtained, with intensity peak at {111}<112> component when cold rolling reduction reaches 80%. Increasing coiling temperature and cold rolling reduction improve γ-fiber intensity and r value, resulting in good deep drawability.
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  Corrosion of Alloy Steel in 30% Ethylene Glycol Solution and CrO2-4 Under Hydrodynamic Condition

  M Niknejad Khomami,I Danaee,A A Attar,M Peykari

  中国钢铁期刊网. 2013, 20(6): 82-87.

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  The electrochemical behavior of steel alloy in 30% ethylene glycol-water solution at different solution rotating speeds was investigated by polarization curves and AC impedance measurements. The results obtained showed that corrosion rate did not change significantly at different rotating speeds. The effect of chromate as the inhibitor was studied and high inhibition efficiency was obtained. It was found that surface passivation occurred in the presence of the inhibitor. The inhibiting effect of the chromate was explained on the basis of the competitive adsorption between the inorganic anions and the aggressive Cl- and the adsorption isotherm basically obeys the Langmuir adsorption isotherm. Thermodynamic parameters for inhibitor adsorption were determined and results reveal that the adsorption process is spontaneous.
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  Elemental Partitioning Characteristics of Equilibrium Phases in Inconel 718 Alloy at 600-1100 ℃

  WEI Xian-ping,,ZHENG Wen-jie,SONG Zhi-gang,LEI Ting,YONG Qi-long,XIE Qing-cheng

  中国钢铁期刊网. 2013, 20(6): 88-94.

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  The optimization of heat treatment and chemical composition for Inconel 718 alloy has been investigated uninterruptedly because of its excellent mechanical properties and metallurgical workability. The species, chemical compositions and content of equilibrium phases of Inconel 718 alloy in the temperature range of 600-1100 ℃ were calculated by using thermodynamic software “Thermo-Calc” and the latest relevant datebase of Ni-base superalloys. A concept of elemental partitioning fraction was used to study the partitioning characteristics of alloying elements in each equilibrium phase at different temperatures, such as Ni, Cr, Fe, Nb, Mo, Al, Ti and C, and some calculation results were confirmed under a scanning transmission electron microscope (STEM). The results showed that the elemental partitioning characteristics with the change of temperature revealed the selective partitioning characteristic of alloying elements in equilibrium phases at different temperatures, such as Nb was mainly distributed in δ and γ′ phase, C in carbides, Al and Ti in γ′ phase and Cr, Mo in Laves phase. At the same time, the effect of the change of component and quantity for each precipitated phase on matrix phase can be helpfully understood, which provided a theoretic foundation to optimize the chemical composition and heat treatment in different environments for Inconel 718 alloy.