2007年, 第14卷, 第6期　刊出日期：2007-12-15

  

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Metallurgy and Metal Working
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  “Redistribution” Effect of Lumpy Zone for Gas Flow in BF

  ZHU Qingtian;CHENG Shusen

  中国钢铁期刊网. 2007, 14(6): 1-0.

  摘要 ( )   可视化   收藏

  The gas flow from tuyere to raceway zone by blasting involves three distributional zones, such as dripping, cohesive, and lumpy zone. The gas flow distribution in lumpy zone directly affects the gas utilization ration and smooth operation in the blast furnace. However, the furnace closeness brings about great difficulty in the study of hightemperature gas flow. The charging and blasting system affecting the gas flow and whether the top gas flow distribution could reflect its inner condition as well as the furnace state, such as hanging or scaffolding, which have become the main problems for the research on gas flow. Recently, several researches overseas studied gas flow distribution using the numerical simulation method; however, such a research was rare amongst the natives. In this study, the flow model of gas in cohesive and lumpy zone was established using the numerical simulation software and the gas flow distributions with uniform distribution of burden permeability, scaffolding of wall, and nonuniform charge level were analyzed. As a result, the effects of cohesive zone and lower parts on the gas flow are very limited and the charge level largely affects the distribution of top gas flow. Therefore, it was found that the distribution of top gas flow could hardly reflect the inner gas flow. The process is called “redistribution” effect, which means that the gas flow after passing through the raceway, dripping, and cohesive zone is distributed when it flows into the lumpy zone.
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  Numerical Simulation of Continuous Tension Leveling Process of Thin Strip Steel and Its Application

  LI Shengzhi;YIN Yuande;XU Jie;HOU Junming;Jaehong YOON

  中国钢铁期刊网. 2007, 14(6): 8-0.

  摘要 ( )   可视化   收藏

  Coldrolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of setup and manipulating are more difficult. With the aid of FE code MSCMARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anticambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were done with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the crosssection of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anticambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.
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  Numerical Simulation of Heat Transfer and Deformation of Initial Shell in Soft Contact Continuous Casting Mold Under High Frequency Electromagnetic Field

  NA Xianzhao;XUE Min;ZHANG Xingzhong;GAN Yong

  中国钢铁期刊网. 2007, 14(6): 14-0.

  摘要 ( )   可视化   收藏

  Heat transfer and deformation of initial solidification shell in soft contact continuous casting mold under high frequency electromagnetic field were analyzed using numerical simulation method; the relative electromagnetic parameters were obtained from the previous studies. Owing to the induction heating of a high frequency electromagnetic field (20 kHz), the thickness of initial solidification shell decreases, and the temperature of strand surface and slit copper mold increases when compared with the case without the electromagnetic filed. The viscosity of flux decreases because of the induction heating of the high frequency electromagnetic field, and the dimension of the flux channel increases with electromagnetic pressure; thus, the deformation behavior of initial solidification shell was different before and after the action of high frequency electromagnetic field. Furthermore, the abatement mechanism of oscillation marks under high frequency electromagnetic field was explained.
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  Affecting Factors and Improving Measures for Converter Gas Recovery

  中国钢铁期刊网. 2007, 14(6): 22-0.

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  To change the undesirable present situation of recovering and using converter gas in steel plants in China, the basic approaches to improving the converter gas recovery rate were analyzed theoretically along with the change curves of the converter gas component content, based on the converter gas recovery system of Baosteel No2 steelmaking plant. The effects of converter device, raw material, air imbibed quantity, recovery restricted condition, and intensity of oxygen blowing on the converter gas recovery rate were studied. Among these, the effects of the air imbibed quantity, recovery restricted condition, and intensity of oxygen blowing are remarkable. Comprehensive measures were put forward for improving the converter gas recovery from the point of devices, etc, and good results were achieved.
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  High Efficient Technology of Steelmaking With Low Silicon Hot Metal on Large Converter

  JIANG Xiaofang;WANG Minglin;YANG Wenyuan;GAN Yong;WANG Yingjun;YU Zuda

  中国钢铁期刊网. 2007, 14(6): 27-0.

  摘要 ( )   可视化   收藏

  To resolve the difficulty in slag formation during steelmaking with low silicon hot metal and to increase productivity, a new 5hole lance was developed by increasing oxygen flow from 50 000 m3/h to 60 000 m3/h. Synthetic slag was added to adjust the slag composition. The problems such as difficulty in dephosphorization and slag adhesion to oxygen lance and hood were settled. Steel production and metal yield were increased and the nozzle life was prolonged through these techniques.
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  Oxidation of Silicon and Boron in Boron Containing Molten Iron

  YANG Zhongdong;LIU Sulan;LI Zhefu;XUE Xiangxin

  中国钢铁期刊网. 2007, 14(6): 32-0.

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  A new process of directly smelting boron steel from boroncontaining pig iron has been established. The starting material boroncontaining pig iron was obtained from ludwigite ore, which is very abundant in the eastern area of Liaoning Province of China. The experiment was performed in a mediumfrequency induction furnace, and Fe2O3 powder was used as the oxidizing agent. The effects of temperature, addition of Fe2O3, basicity, stirring, and composition of melt on the oxidation of silicon and boron were investigated respectively. The results showed that silicon and boron were oxidized simultaneously and their oxidation ratio exceeded 90% at 1 400 ℃. The favorable oxidation temperature of silicon was about 1 300-1 350 ℃. High oxygen potential of slag and strong stirring enhanced the oxidation of silicon and boron.
Material
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  Design of TRIP Steel With High Welding and Galvanizing Performance in Light of Thermodynamics and Kinetics

  LI Lin;DE COOMAN B C;LIU Rendong;VLEUGELS J;ZHANG Mei;SHI Wen

  中国钢铁期刊网. 2007, 14(6): 37-0.

  摘要 ( )   可视化   收藏

  A new type of transformation induced plasticity (TRIP) steel with not only high strength and high ductility but also superior welding and galvanizing properties was designed and developed recently. Low carbon and low silicon content were preliminarily selected with the aim of meeting the requirements of superior quality in both welding and galvanizing. Phosphorus was chosen as one of the alloying elements, because it could reduce carbon activity in cementite and increase the stability of austenite. In addition, the possibility of phosphorus segregating at grain boundary was also discussed by thermodynamics as well as kinetics. Phase diagram was estimated at high temperature and the composition of the steel was then selected in the hyperperitectic range to avoid problems, which might occur in sheet steel continuous casting. Phase diagram in the intercritical temperature was estimated for the steel to obtain the starting temperature of fast cooling. For understanding the minimum rate of fast cooling, pearlite growth kinetics was calculated with selfdeveloped diffusion coefficients of elements in grain boundary. Overaging temperature was determined through the calculation of T0 temperature by both equilibrium and paraequilibrium assumptions, which was different from the current determination, which is only based on an equilibrium estimation.
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  Prediction of Rolling Load, Recrystallization Kinetics, and Microstructure During Hot Strip Rolling

  XU Yunbo;YU Yongmei;LIU Xianghua;WANG Guodong

  中国钢铁期刊网. 2007, 14(6): 42-0.

  摘要 ( )   可视化   收藏

  The recrystallization kinetics and grain size models were developed for the CMn and niobiumcontaining steels to describe the metallurgical phenomenon such as softening, grain growth, and strain accumulation. Based on the recrystallization kinetics equations, the mean flow stress and the rolling load of each pass were predicted and the optimum rolling schedule was proposed for hot strip rolling. The austenite grain refinement is associated with the addition of niobium, the decrease of starting temperature of finish rolling, and the reduction of finished thickness. The mean flow stress curve with a continuous rising characteristic can be usually observed in the finish rolling of niobiumcontaining steel, which is formed as a result of the heavy incomplete softening and strain accumulation. The predicted rolling loads are in good agreement with the measured ones.
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  Numerical Simulation on Carburizing and Quenching of Gear Ring

  SONG Guangsheng;LIU Xianghua;WANG Guodong;XU Xiangqiu

  中国钢铁期刊网. 2007, 14(6): 47-0.

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  The carburizing process of the gear ring was simulated by taking into account the practical carburizing and quenching techniques of the gear ring and by solving the diffusion equation. The carbon content distribution in the carburized layer was obtained. Based on the results, the quenching process of the gear ring was then simulated using the metallic thermodynamics and FEM; it was found that the carburization remarkably affects the quenching process. Microstructures and stress distributions of the gear ring in the quenching process were simulated, and the results are confirmed by experiments.
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  Effect of Boron on Delayed Fracture Resistance of MediumCarbon High Strength Spring Steel

  NIE Yihong;HUI Weijun;FU Wantang;WENG Yuqing

  中国钢铁期刊网. 2007, 14(6): 53-0.

  摘要 ( )   可视化   收藏

  The delayed fracture behavior of mediumcarbon high strength spring steel containing different amounts of boron (0000 5%, 0001 6%) was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron content from 0000 5% to 0001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350 ℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initiation area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3(C, B) phase.
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  Physical Simulation and Experimental Examination of εCu Particles Dissolution Evolution During Welding of Copper Precipitation Strengthening Steel

  WANG Qingfeng;SHANG Chengjia;CHEN Dawei;CAI Jianwei;CHEN Weichang;

  中国钢铁期刊网. 2007, 14(6): 58-0.

  摘要 ( )   可视化   收藏

  The kinetics of εCu particles dissolution in the matrix during welding of a copperprecipitation strengthening steel was determined by a combination of GleebleTM physical simulation, TEM examination and hardness measurement. The εCu particles underwent a coarsening and part dissolution and then complete dissolution reaction as the peak temperature increased from 750 to 1 000 ℃, which resulted in the decrease in the number density of εCu particles and hardness in the heataffected zone (HAZ). The results can be used to understand the evolution of this transformation and a softening behavior of the HAZ during welding of this type of steel.
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  Effects of Applied Stresses on Martensite Transformation in AISI4340 Steel

  ZHAO Hongzhuang;Seokjae LEE;Youngkook LEE;LIU Xianghua;WANG Guodong

  中国钢铁期刊网. 2007, 14(6): 63-0.

  摘要 ( )   可视化   收藏

  This study aims at the experimental analysis of the transformation induced plasticity (TRIP) phenomenon. Experiments are conducted in which martensite is allowed to grow under the influence of a series of externally applied stresses. The magnitude of the applied stresses is less than 67% of the yield strength of austenite σγ(Ts). Since there is no obvious difference between the transformation plasticity under tension and the compression for the lower applied stresses, only compressive stresses are applied. The results confirm that the transformation plasticity is proportional to the applied stress if the latter does not exceed 67% of σγ(Ts). The TRIPstrain, the kinetics, and their dependence on the applied stresses are studied. The comparison between calculated results and experimental results shows that the model accurately describes the phenomenon.
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  Microstructure Variation and Hardness Diminution During Low Cycle Fatigue of 55NiCrMoV7 Steel

  ZHANG Zhanping;QI Yuhong;DELAGNES Denis;BERNHART Gérard

  中国钢铁期刊网. 2007, 14(6): 68-0.

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  The influence of temperature and hardness level on the cyclic behavior of 55NiCrMoV7 steel, and the microstructure variation and hardness diminution during low cycle fatigue behavior were investigated. By means of SEM and XRD, the modality of carbides and the fullwidth halfmaximum (FWHM) of martensite (211) [M(211)] of Xray diffraction spectrum in fatigue specimen were studied. The results showed that the cyclic stress response behavior generally showed an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. The fatigue behavior of the steel is closely related to the hardness level. The hardness diminution and the variation of halfwidth M(211) are remarkably influenced by the interaction between the cyclic plastic deformation and the thermal loading when the fatigue temperature exceeds the tempering temperature of the steel.
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  Improvement of Mechanical Properties of CrNiMoCuTi Stainless Steel With Addition of Vanadium

  S M Abbasi;A Shokuhfar

  中国钢铁期刊网. 2007, 14(6): 74-0.

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  The effect of vanadium (V) addition on the mechanical properties of a CrNiMoCuTi stainless steel was studied and its influence on microstructural changes was also investigated. Results indicate that the structure of the solutiontreated specimens mainly comprises of austenitemartensite, and adding V leads to the formation of a considerable amount of ferrite. Under this condition, austenite phase is not mechanically stable, and transforms to martensite by plastic deformation. The addition of 05% - 10% (in mass percent) of V increases the hardness and the strength of the 80% cold rolled and aged steel, without any effect on ductility. Improvement in mechanical properties is presumably attributed to the formation of a small amount of ferrite in the primary structure, and the formation of certain precipitates is accelerated by the addition of V during aging. By contrast, excessive V decreases the strength and ductility simultaneously. This is due to the strong effect of ferrite formation compared to the beneficial effect of precipitation. The loss of ductility caused by adding higher amount of V is due to the formation of ferrite phases which in turn are suitable nucleation sites for crack propagation.