2014年, 第21卷, 第9期　刊出日期：2014-09-15

  

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Metallurgy and Metal Working
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  Numerical Analysis of Fluctuation Behavior of Steel/Slag Interface in Continuous Casting Mold with Static Magnetic Field

  An-yuan DENG,Lin XU,En-gang WANG,Ji-cheng HE

  中国钢铁期刊网. 2014, 21(9): 809-816.

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  Utilizing ANSYS CFX commercial software and volume fraction of fluid (VOF) model, fluctuation behavior of steel/slag interface was numerically simulated in continuous casting mold with static magnetic field, and the influence of metal jet characteristics on the behavior of steel/slag interface was investigated. The results indicated that the behavior of steel/slag interface is similar at different process parameters, which is closely related to the characteristic of the flow field. The steel/slag interface has an obvious trough characteristic, which can be divided into three zones: frontal valley zone, back valley zone and horizontal zone; as the magnetic flux density increases, the fluctuation of liquid level increases firstly and then decreases, and a reasonable magnetic flux density can make steel/slag interface obtain a relatively flat interface, which can prevent slag from being entrapped into liquid steel. For a thin slab continuous casting process, when the casting speed is 4 m/min, a reasonable magnetic flux density is about 0.5 T, and the interfacial fluctuation is weaker. No matter the position of magnetic field is horizontal or vertical, for different operating parameters, there is a corresponding reasonable magnetic field position where the steel/slag interface fluctuation can be properly controlled and slag entrapment can be prevented.
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  Study and Application of Camber Control Model of Intermediate Slab in Rough Rolling

  Hai-yu WANG,Quan YANG,Xiao-chen WANG,Feng HE,Yu-feng CHEN

  中国钢铁期刊网. 2014, 21(9): 817-822.

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  In order to solve the camber problem of intermediate slab in a domestic conventional hot rolling mill, a three-dimensional elastic-plastic dynamic model was built through finite element method to quantitatively calculate the influence of lateral flow factors in different entry thicknesses, reductions, reduction ratios differences on both sides and width factors. Thus, the extending difference at outlet of intermediate slab in length was transformed into thickness difference on both sides by the results, and then the tilting value of roll gap reduction to control the camber was calculated. Based on the above results, the camber control model of intermediate slab in rough rolling was established. The practical application on the rough rolling mill obtained a decent control effect, and it proved that this model had a high accuracy.
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  Principle of Multi-roller Straightening Process and Quantitative Resolutions of Straightening Strategies

  Jing YIN,,Jun ZHAO,Shi-yan WANG,Xian-song WAN,Yue-lin LI

  中国钢铁期刊网. 2014, 21(9): 823-829.

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  The multi-roller straightening process of section steel is analyzed by the springback theory of small curvature plane bending. The theoretical analysis results prove the curvature unification in straightening process and clearly reveal the principle of the multi-roller straightening process. The principle can be described as: the initial curvatures are reduced by several times anti-bending; meanwhile the initial curvature differences are diminished and the residual curvatures are unified; finally, the member after curvature unification is straightened by the last anti-bending. With the plastic region ratios becoming larger, the initial curvatures are more easily unified in straightening process. Based on the plastic region ratios and the required number of roller systems for unifying the initial curvatures, the large deformation straightening strategy and the small deformation straightening strategy are redefined. The new definition provides an important theoretical basis for setting reliable reduction rules. Through the theoretical analysis results, a new straightener design philosophy is proposed to improve the straightening quality and further increase the adjustment precision as well as the flexibility of the last roller system. The adjustable end roller emerges as the times required, achieving a good effect in practical application.
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  Modeling and Analysis of Interstand Tension Control in 6-high Tandem Cold Rolling Mill

  Xin ZHANG,Shu-zong CHEN,Hao-yu ZHANG,Xi-wen ZHANG,Dian-hua ZHANG,Jie SUN

  中国钢铁期刊网. 2014, 21(9): 830-836.

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  The interstand tension control is one of the most important ways to meet tight tolerances for strip product quality during tandem cold rolling process. Using coordinate analysis and parabolic approximation for the mass flow balance principle, the strip velocities eliminating the use of forward slips and backward slips were calculated. In order to reduce the effect of roll eccentricity on the tension measurement, a filter based on bilinear transformation was designed. Applying a first-order Taylor series approximation, the transfer function matrix model of interstand tension stress was derived. The actual measurements on-site and the final calculation results showed that the established model had high calculation accuracy and was beneficial for interstand tension control of tandem cold rolling process.
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  Spatial Vibration and Its Numerical Analytical Method of Four-high Rolling Mills

  Yong-jiang ZHENG,Guang-xian SHEN,Yi-geng LI,Ming LI,Hong-min LIU

  中国钢铁期刊网. 2014, 21(9): 837-843.

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  The rolls in contemporary four-high mills cannot be maintained parallel during the rolling process. Therefore, four-high rolling mill vibrations take place in six degree of freedom (DOF) leading to spatial behaviors involving vertical, horizontal, axial, torsional, cross and swinging vibration modes resulting in complex relative motions between the rolls.Two numerical methods, modified Riccati-transfer matrix method (Riccati-TMM) and finite element method (FEM), are presented to analyze a spatial vibration characteristic of two four-high rolling mills with different stability. The natural frequency and mode shape of four-high rolling mills are obtained, and the clearance has a great effect on natural frequency and mode shape. In addition, field testing experiment is also conducted to measure natural frequency by power spectrum analysis of rolling mill vibration. Experimental results basically agree with those calculated by Riccati-TMM and FEM, which means that the Riccati-TMM and the FEM can be used for analysis of spatial vibration of four-high rolling mill. Meanwhile, the spatial vibration shows more compound vibration behaviors and the negative effect of horizontal, vertical, cross and swinging vibration modes are effectively controlled after redesign of rolling mill. These advantages have a great significance for the rolling mill to be operated with a much higher rolling speed and improved yield of products.
Material
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  Texture, Grain Boundary Characterization and Segregation of Phosphorus in an Annealed Interstitial Free Steel

  Xin-li SONG,Kun PENG,Ze-xi YUAN,Juan JIA,Jing LIU,Li-xia FAN

  中国钢铁期刊网. 2014, 21(9): 844-848.

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  The {111}∥ND plane texture, grain boundary characterization and grain boundary segregation of phosphorus are investigated for the phosphorus added high strength interstitial free (IF) steel annealed at 810 ℃ for 60 s to 180 s. The results show that the maximum volume fraction of {111}∥ND plane texture is about 85% and the grain boundary segregation peak of phosphorus is about 14 at.% for the steel annealed at 810 ℃ for 120 s. The Σ3 and other low-ΣCSL (coincident site lattice) boundaries are lowest for the steel annealed for 120 s. Segregation of phosphorus is also found at low angle grain boundaries.
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  Sintering Behavior of Porous Titanium Fiber Materials

  Shi-feng LIU,Zheng-ping XI,Hui-ping TANG,Xin YANG,Zhao-hui ZHANG,Quan-ming LIU

  中国钢铁期刊网. 2014, 21(9): 849-854.

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  The porous titanium fiber materials with open porosity were successfully prepared by the vacuum sintering technology. The morphology characteristics of sintering neck of porous titanium fiber materials were investigated by scanning electron microscopy (SEM). The results show that the formation and growth of sintering neck of porous titanium fiber material approximately follow the rule that the primary mechanism is grain boundary diffusion and subsidiary mechanisms are other diffusion mechanisms during the sintering process. The formation and growth of the sintering neck depend mainly on the sintering temperature and slightly on the soaking time. The sintering system of porous titanium fiber material was determined and the equation of the sintering neck′s length was established.
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  Migration of δ/γ Interface in Low Carbon Steels during Continuous Cooling

  Qing-chun LI,Yong-feng QI,Shu XU,Chao WANG,Guo-wei CHANG

  中国钢铁期刊网. 2014, 21(9): 855-861.

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  The δ-ferrite to γ-austenite phase transformation process of low carbon steel was observed in-situ under a confocal scanning laser microscope and the influence of manganese and chromium on the migration of δ/γ interphase boundary during the δ to γ phase transformation was studied. It was found that the δ/γ interphase boundary becomes unstable with the decrease of temperature, from planar to curved morphology during the δ to γ phase transformation of Fe-0.08C steel and Fe-0.08C-0.8Mn steel. But in Fe-0.08C-0.8Cr steel, the δ/γ interphase boundaries are stable with planar morphology during the whole δ-ferrite to γ-austenite transformation. The destabilization of δ/γ interphase boundary in Fe-0.08C and Fe-0.08C-0.8Mn steels results from high degree of supercooling and sub-boundaries in γ, respectively. The stabilization of δ/γ interphase boundary in Fe-0.08C-0.8Cr steel results from the slow diffusion rate of carbon atom induced by the addition of chromium.
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  Healing Behavior of Micropores in Powder Metallurgy 316L Stainless Steel during Hot Forging and Heat Treatment

  Ying KAN,,Shi-hong ZHANG,Li-wen ZHANG,Ming CHENG,Hong-wu SONG,Hong-wei LU

  中国钢铁期刊网. 2014, 21(9): 862-868.

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  The healing behavior of micropores in powder metallurgy (P/M) 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a result of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense materials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelerating the recrystallization according to the difference of deformation temperatures.
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  Experimental and Simulation Studies on Fabricating GCr15/40Cr Bimetallic Compound Rollers Using Electroslag Surfacing with Liquid Metal Method

  Lei RAO,Shuang-jun WANG,Jian-hua ZHAO,Mao-peng GENG,Gang DING

  中国钢铁期刊网. 2014, 21(9): 869-877.

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  Electroslag surfacing with liquid metal (ESSLM) is an excellent method for producing high-quality bimetallic compound rollers. The quality of each compound roller is primarily determined by the metallurgical quality of the combined interface. A GCr15/40Cr compound roller is produced using an ESSLM non-consumable electrode electroslag heating method. The temperature and electric fields produced by the ESSLM system are calculated. As the roller core moves downward in the mold, it passes through five sections: the preheating section, the rapid heating section, the temperature homogenizing section, the bimetal fusing section and the cooling section which listed from the top to bottom of the mold, respectively. The temperature distribution and the degree of the surface temperature fluctuation in the roller core are different for each section. Near the combined interface, four layers are found from the roller core to the cladding layer: the remelting layer, the fusion layer, the interface solidification layer and the chilling layer, respectively. Among these, the fusion and interface solidification layers are the key transition zones that greatly influence the combination quality. The surface temperature of the roller core prior to cladding is mainly determined by the drawing velocity, and the thickness of the transition layer increases as the drawing velocity decreases. A transition layer that is too thick or too thin will reduce the mechanical properties at the combined interface. Therefore, the drawing velocity should be limited to a moderate range to produce a satisfactory bimetallic compound roller.
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  Influence of Mo on Growth and Coarsening of Nanometer-sized Carbides in Low-alloy Ferritic Steels Containing Ti

  Bin-hao HU,Qing-wu CAI,Hui-bin WU

  中国钢铁期刊网. 2014, 21(9): 878-885.

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  By optical microscopy, transmission electron microscopy and energy dispersive spectroscopy, the changes with aging time in size, composition and distribution of nanometer-sized (Ti,Mo)C precipitated in Ti-Mo low-alloy ferritc steel have been studied in comparison with that of nanometer-sized TiC precipitated in Ti low-alloy ferritc steel. It was found that the growth rate of (Ti,Mo)C in Ti-Mo steel was less than that of TiC in Ti steel. Nanometer-sized carbides formed at 650 ℃ (or 550 ℃) for 55 h were at transitional stage from growth to coarsening. When aging time reaches 55 h, the coarsening rates of nanometer-sized carbides in Ti and Ti-Mo steel tend to be the same and invariable. The influence of Mo on growth and coarsening of nanometer-sized carbides tends to decrease with increasing aging time, and Mo contents in nanometer-sized carbides with the same size at different aging time were different.
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  Formation of AlN Nano Particles Precipitated in St-14 Low Carbon Steel by Micro and Nanoscopic Observations

  Amirsalar Khandan,Ebrahim Karamian,Mojdeh Faghih,Allain Bataille

  中国钢铁期刊网. 2014, 21(9): 886-890.

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  In low carbon steels, dissolution and precipitation of the second phases such as carbides and nitrides during annealing cycles can affect the final structure and properties of the materials. The interaction of above processes depends on parameters such as reheating temperature, heating rate, annealing temperature, soaking time and finishing temperature in hot rolling stage before cold rolling. The effects of heating rate and annealing temperature on the microstructure and hardness were investigated. Two heating rates for annealing temperatures of 550, 610 and 720 ℃ were applied on cold-rolled specimens and St-14 low carbon steel, which were immediately quenched after isothermal annealing. The intercept method was used to measure average grain sizes. However, resulted microstructures are different for the two heating rates. While pancaked structures were observed in specimens annealed with low heating rate, in samples annealed with high heating rate, equiaxed microstructures were observed. Vickers micro-hardness values decreased at all temperatures, which were more significant at higher temperatures. At longer annealing time, signs of increase of hardness values were detected. All results and observations consistently suggest that a precipitation process has occurred concurrently with restoration processes during annealing. In addition, the energy dispersive spectroscopy analysis resulted from transmission electron microscopic micrographs have proved that the nano particles precipitated in grain boundaries are AlN.
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  Surface Nanocrystallization of Nb-Ti Stabilized 439M Ferritic Stainless Steel

  Yao-chun ZHANG,Chao CHEN,,Cheng-jia SHANG,Dong-yang LI

  中国钢铁期刊网. 2014, 21(9): 891-896.

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  A new nanocrystallization process was designed, which included punching the surface coating to generate dislocation network or cells and recovery treatment to turn the dislocation cells into nano-sized grains. The effort was made to increase the service life of Nb-Ti stabilized 439M stainless steel surface with medium passive ability, particularly to enhance the outmost surface layer by nanocrystallization for improving resistances to corrosion. Electrochemical properties, electron work functions (EWFs), nano-mechanical properties of the nanocrystallized surfaces were investigated. It was demonstrated that the nanocrystallized 439M stainless steel surface exhibited improved resistance to corrosion in 0.5 mol/L H2SO4 solution. However, the nanocrystallized 439M stainless steel surface exhibited decreased resistance to corrosion in 3.5% NaCl solution.