钢铁研究学报(英文版)
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2014 Vol. 21 No. 2
Published: 2014-02-15
135
Yan LIU,Zi-mu ZHANG,Sano MASAMICHI,Jun ZHANG,Pin SHAO,Ting-an ZHANG
Improvement of Impeller Blade Structure for Gas Injection Refining under Mechanical Stirring
The impeller blade structure for gas injection refining under mechanical stirring has been explored by water model experiments. A sloped swept-back blade impeller is proposed for the purpose. The central part of the impeller is disk- or plate-shaped, and the blades are fitted to the side of the disk or plate. In addition, a disk is put on the top side of the impeller blades. The impeller can strengthen the radial and downward flow between the blades and weaken the swirl flow in the zone above the impeller. These effects on flow phenomena are favorable for disintegration and wide dispersion of bubbles which are injected from a nozzle attached to the center of the underside of the impeller. In addition, the sloped swept-back impeller requires less power consumption. The impeller shaft should be placed away from the vessel center so as to disperse the injected bubbles widely in the bath under mechanical stirring even with unidirectional impeller rotation and without installing baffles. The number of gas holes in the nozzle and the direction of gas injection have a little effect on the bubble disintegration and dispersion in the bath. Highly efficient gas injection refining can be established under the conditions of proper impeller size, larger nozzle immersion depth, larger eccentricity and rotation speed of the impeller. The sloped swept-back blade impeller can decrease the power consumption and yet improve the bubble disintegration and wide dispersion in the bath.
2014 Vol. 21 (2): 135-143 [
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144
Yong ZHANG,Jue TANG,Man-sheng CHU,Yang LIU,Shuang-yin CHEN,Xiang-xin XUE
Optimization of BF Slag for High Cr2O3 Vanadium-titanium Magnetite
In order to clarify the slag system of high Cr2O3 vanadium-titanium magnetite smelting in BF (blast furnace), the melting properties of slag samples prepared by analytically pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high Cr2O3 vanadium-titanium magnetite was obtained, which contained 10% MgO, 8% TiO2 and 15% Al2O3, with the binary basicity being 115. In addition, the effects of basicity, MgO, TiO2 and Al2O3 on slag melting properties were investigated by single factor test, and the results showed that, with increasing the basicity or TiO2 content, melting temperature (Tm) increased, whereas initial viscosity (η0) and high-temperature viscosity (ηh) decreased. With increasing the MgO content, Tm decreased firstly and then increased. With increasing the Al2O3 content, Tm increased, and η0 and ηh decreased firstly and then increased.
2014 Vol. 21 (2): 144-150 [
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151
Jian-liang ZHANG,Guang-wei WANG,Jiu-gang SHAO,Hai-bin ZUO
Comprehensive Mathematical Model and Optimum Process Parameters of Nitrogen Free Blast Furnace
According to different energy utilization in different regions, blast furnace is divided into raceway zone, bottom heat exchange zone (BHZ), thermal reserve zone (TRZ), and top heat exchange zone (THZ), and a mathematical model of nitrogen free blast furnace (NF-BF) is established. The optimum process parameters of two kinds of nitrogen free blast furnaces are calculated by the new mathematical model. The results show that for the nitrogen free blast furnace with a single row of tuyeres, the optimum process parameters are coke ratio of 220 kg/t, coal ratio of 193 kg/t, and volume of recycling top gas of 577 m3/t; for two rows of tuyeres, the process parameters are coke ratio of 202 kg/t, coal ratio of 211 kg/t, volume of recycling top gas in upper area of 296 m3/t, and volume of recycling top gas in lower area of 295 m3/t. Energy balances are reached in different regions. Theoretical combustion temperature (TCT) in raceway zone is largely affected by different processes, and a lower TCT should be adopted for the single row of tuyeres, but for two rows of tuyeres, a higher TCT should be maintained. Compared with traditional blast furnace, in NF-BF, the emission of CO2 would be reduced by 4591% and 4902% for a single row of tuyeres and two rows of tuyeres, respectively, and combined with CO2 sequestration technology, zero emission of CO2 could be realized.
2014 Vol. 21 (2): 151-158 [
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159
De-wei LI,Zhi-jian SU,Katsukiyo MARUKAWA,Ji-cheng HE
Simulation on Effect of Divergent Angle of Submerged Entry Nozzle on Flow and Temperature Fields in Round Billet Mold in Electromagnetic Swirling Continuous Casting Process
A new process for swirling flow generation in the submerged entry nozzle (SEN) in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow by Lorentz force. The flow and temperature fields in the SEN and round billet mold with electromagnetic swirling were numerically simulated and then verified by the electromagnetic swirling model experiment of low melting point alloy. The effects of divergent angle of the SEN on the flow and temperature fields in mold with electromagnetic swirling were investigated. The electromagnetic swirling flow generator (EMSFG) could effectively induce swirling flow of molten steel in the SEN, which consequently improved greatly the flow and temperature fields in the mold. Below the nozzle outlet in mold, with the increase of divergent angle, the stream of bulk flow diverged more widely, the high temperature zone shifted up, and the temperature field became more uniform. Above the nozzle outlet in mold, with 350 A electromagnetic swirling, when the divergent angle of the SEN increased, the upward flow velocity and the meniscus temperature first increased and then decreased. With a divergent angle of 60°, the upward flow velocity and meniscus temperature reaced the largest value.
2014 Vol. 21 (2): 159-165 [
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166
Jing GUO,Shu-sen CHENG,Zi-jian CHENG,
Characteristics of Deoxidation and Desulfurization during LF Refining Al-killed Steel by Highly Basic and Low Oxidizing Slag
Steel and slag samples were taken at the start and the end of LF refining for steel plate cold common (SPCC), in the compact strip production (CSP) process, and at the same time, the temperature and oxygen activity a［O］ were measured by using an oxygen sensor. Furthermore, inclusions in steel samples were monitored by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). It was confirmed that a［O］ in liquid steel was in equilibrium with inclusion rather than with top slag during LF refining. Desulfurization was related to deoxidation since a［O］ at slag-steel interface was clarified to be very close to that in liquid steel under the specific condition in LF with intense stirring by argon blowing and refined by highly basic low oxidizing slag for Al-killed steel. Sulfur partition ratio (LS) was very sensitive to a［O］. Since a［O］ increased rapidly with temperature rise, it not only offset promotion to desulfurization reaction with temperature rise but decreased LS. For Al-killed steel, the modification of Al2O3 for lowering the activity of Al2O3 in inclusion was believed to be favorable for both deoxidation and desulfurization during LF refining.
2014 Vol. 21 (2): 166-173 [
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174
Mao-xiang CHU,,An-na WANG,Rong-fen GONG,,Mo SHA
Multi-class Classification Methods of Enhanced LS-TWSVM for Strip Steel Surface Defects
Considering strip steel surface defect samples, a multi-class classification method was proposed based on enhanced least squares twin support vector machines (ELS-TWSVMs) and binary tree. Firstly, pruning region samples center method with adjustable pruning scale was used to prune data samples. This method could reduce classifier′s training time and testing time. Secondly, ELS-TWSVM was proposed to classify the data samples. By introducing error variable contribution parameter and weight parameter, ELS-TWSVM could restrain the impact of noise samples and have better classification accuracy. Finally, multi-class classification algorithms of ELS-TWSVM were proposed by combining ELS-TWSVM and complete binary tree. Some experiments were made on two-dimensional datasets and strip steel surface defect datasets. The experiments showed that the multi-class classification methods of ELS-TWSVM had higher classification speed and accuracy for the datasets with large-scale, unbalanced and noise samples.
2014 Vol. 21 (2): 174-180 [
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181
Fei HE,,Dong-feng HE,,An-jun XU,,Hong-bing WANG,Nai-yuan TIAN,
Hybrid Model of Molten Steel Temperature Prediction Based on Ladle Heat Status and Artificial Neural Network
Aiming at the characteristics of the practical steelmaking process, a hybrid model based on ladle heat status and artificial neural network has been proposed to predict molten steel temperature. The hybrid model could overcome the difficulty of accurate prediction using a single mathematical model, and solve the problem of lacking the consideration of the influence of ladle heat status on the steel temperature in an intelligent model. By using the hybrid model method, forward and backward prediction models for molten steel temperature in steelmaking process are established and are used in a steelmaking plant. The forward model, starting from the end-point of BOF, predicts the temperature in argon-blowing station, starting temperature in LF, end temperature in LF and tundish temperature forwards, with the production process evolving. The backward model, starting from the required tundish temperature, calculates target end temperature in LF, target starting temperature in LF, target temperature in argon-blowing station and target BOF end-point temperature backwards. Actual application results show that the models have better prediction accuracy and are satisfying for the process of practical production.
2014 Vol. 21 (2): 181-190 [
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191
Zhun-li TAN,Kai-kai WANG,Gu-hui GAO,Xiao-lu GUI,Bing-zhe BAI,,Yu-qing WENG
Mechanical Properties of Steels Treated by Q-P-T Process Incorporating Carbide-free-bainite/martensite Multiphase Microstructure
Quenching-partitioning-tempering (Q-P-T) process were applied to a quenched carbide-free bainite/martensite (CFB/M) multiphase steel 40Mn2Si2Cr and its effect on the mechanical properties was studied. The results showed that the partitioning time of Q-P-T treatment can be increased greatly to 90 min or even longer. The tensile strength, elongation and product of strength and elongation (PSE) of the experimental steel can achieve 1650 MPa, about 20% and over 33 GPa·%, respectively. The significant increase of partitioning time and excellent mechanical properties could be related to the CFB microstructure introduced in the quenching process during the Q-P-T treatment.
2014 Vol. 21 (2): 191-196 [
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197
Li-juan ZHU,,Zheng-wei GU,Hong XU,Yi L,Jiang CHAO
Modeling of Microstructure Evolution in 22MnB5 Steel during Hot Stamping
Automobile manufacturers have been increasingly adopting hot-stamped parts for use in newly designed vehicles to improve crash worthiness and fuel efficiency. However, the simulation of hot stamping is rather complex and challenging, and further research still needs to be done on hot stamping hardening mechanism. The microstructure evolution and hardening mechanisms during hot stamping of 22MnB5 steel were thoroughly investigated, using information provided in the literatures as well as experimental results. New models were developed to predict the grain growth during heating and the flow stress of a manganese boron steel (22MnB5) with high hardenability by the Gleeble simulation experimental results. The deformed austenite decomposition during stamping and quenching was emphatically quantified based on the transformation thermodynamic and kinetic theories, and the relationship of microstructure to properties was analyzed. The results showed that the optimal process to obtain homogeneous and small lath martensite is heating at 900-950 ℃ for 5 min and then quenching at 50 ℃/s with a pressing time about 8 s.
2014 Vol. 21 (2): 197-201 [
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202
Xiao-meng ZHANG,Lian-qi WEI,Peng LIU,Sen WANG,Shu-feng YE,Yun-fa CHEN
Influence of Protective Coating at High Temperature on Surface Quality of Stainless Steel
A ceramic matrix coating for minimizing steel loss of stainless steel at high temperatures was prepared by handled air-spraying technique, and the influence of coating on surface quality of stainless steel was mainly investigated in laboratory. Experimental results showed that the protective coating reduced the oxidation of stainless steel by more than 91% and minimized high-temperature scaling and also enhanced steel surface quality. The scales of coated specimen were removed completely and the scales of uncoated specimen were partly residual on the surface after cooling process. Mn-rich and Fe-rich zones were found in the oxides. The Cr2O3 found in scales came from the underlying stainless steel and formed a Cr-rich layer along the spalled surface.
2014 Vol. 21 (2): 202-207 [
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208
Jie SHI,Jun HU,,Chang WANG,Cun-yu WANG,Han DONG,Wen-quan CAO
Ultrafine Grained Duplex Structure Developed by ART-annealing in Cold Rolled Medium-Mn Steels
The microstructural evolutions of the cold rolled Fe-01C-5Mn steel during intercritical annealing were examined using combined advanced techniques. It was demonstrated that intercritical annealing results in an ultrafine granular ferrite and austenite duplex structure in cold rolled 01C-5Mn steel. The strong partitioning of manganese and carbon elements from ferrite to austenite was found during intercritical annealing by scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD). Strong effects of boundary characters on the austenite formation were indicated by austenite fast nucleation and growth in the high angle boundaries but sluggish nucleation and growth in the low angle boundaries. The ultrafine grained duplex structure in 01C-5Mn was resulted from the the sluggish Mn-diffusion and the extra high Gibbs free energy of ferrite phase. Based on the analysis of the microstructure evolution, it was pointed out that the intercritical annealing of the medium-Mn steels could be applied to fabricate an ultrafine duplex grained microstructure, which would be a promising approach to develop the 3rd generation austomobile steels with excellent combination of strength and ductility.
2014 Vol. 21 (2): 208-214 [
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215
Sheng LIU,Hui-bin WU,Xiao LI,Hai-tao JIANG,Di TANG
Characterizing the Structure Evolution of Tertiary Scale during Simulated Coiling by EBSD
An oxide scale formed at 900 ℃ for 60 s in dry air was subjected to the simulated coiling processed with different coiling temperatures. The phase transformation behavior, especially the orientation distribution of the oxide scale, was analyzed using electron backscattered diffraction (EBSD) technique. When cooling from the coiling temperature of 650 ℃, the scale consists of Fe3O4 layer, FeO layer and Fe3O4 seam. The Fe3O4 precipitates are observed in the FeO grains of the scale formed with the coiling temperature of 550 and 450 ℃. With the coiling temperature of 350 ℃, the decomposition of FeO is suppressed due to the low temperature. The Fe3O4 grains, which are decomposed from FeO, has the same orientation as the parent FeO grains. Moreover, the FeO grains, of which the growth direction is parallel to <001>, is easier to decompose into Fe3O4 than the grains with other orientations.
2014 Vol. 21 (2): 215-221 [
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222
Yong-quan HE,Tao JIA,Xiao-jiang LIU,Guang-ming CAO,Zhen-yu LIU,Jun LI,
Hot-dip Galvanizing of Carbon Steel after Cold Rolling with Oxide Scale and Hydrogen Descaling
A new processing method for producing hot-dip galvanized steel is designed and tested, in which pickling is skipped. Hot-rolled low carbon steel sheets are rolled with oxide scale in an experimental mill at room temperature, prior to annealing under a 20% hydrogen reducing atmosphere and galvanizing on a hot-dip galvanizing simulator. Micro-cracks formed in the oxide scale during cold rolling roughen the steel surface and enlarge the specific surface. Through-thickness cracks provide transport channels for hydrogen, and hence the reduction of oxide scale is enhanced. When the sheet is dipped in the zinc bath, cracks are submerged by liquated zinc and the defects are not distinct after hot-dip galvanizing. The overlay coating occludes with rough surface of the sheet, whereby a superior coating adherence is realized.
2014 Vol. 21 (2): 222-226 [
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227
Lin-na DUAN,,Yu CHEN,Qing-you LIU,Shu-jun JIA,Cheng-chang JIA
Microstructures and Mechanical Properties of X100 Pipeline Steel Strip
Dynamic CCT (continuous cooling transformation) curves and effects of microstructures and M/A islands of X100 hot rolled strip on mechanical properties were studied by means of a thermal simulator, a scanning electron microscope (SEM), a transmission electron microscope (TEM), a digital micro-hardness tester and Image-Pro Plus analysis software. The results show that high contents of C and Mo can make transformation lines of acicular ferrite and bainite shift rightward. High Mo tested strip has higher strength and micro-hardness and lower toughness than the other one because lath bainite appears instead of quasi-polygonal ferrite. Tested strip with granular bainite, lath bainite and M/A islands has better mechanical properties and in the microstructures lath bainite content is around 365% and M/A islands are fine and disperse in the matrix.
2014 Vol. 21 (2): 227-232 [
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233
Qing-yun SHA,Da-hang LI,Gui-yan LI
Dynamic and Static Recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel
The dynamic recrystallization (DRX) and static recrystallization (SRX) behaviour of coarse-grained austenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1150 ℃ at a strain rate of 01-5 s-1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine-grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained austenite is mainly retarded by coarse grain size and Nb in solution during rough rolling.
2014 Vol. 21 (2): 233-239 [
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240
Erdem Atar,zgür Alpaslan,,zgür elik,Hüseyin imenolu
Tribological Properties of CrN Coated H13 Grade Tool Steel
The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were deposited by the arc physical vapor deposition (PVD) before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by following the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.
2014 Vol. 21 (2): 240-245 [
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246
Masoud RAKHSHKHORSHID,Sayyed-Amin TEIMOURI SENDESI
Bayesian Regularization Neural Networks for Prediction of Austenite Formation Temperatures (Ac1 and Ac3)
A neural network with a feed forward topology and Bayesian regularization training algorithm is used to predict the austenite formation temperatures (Ac1 and Ac3) by considering the percentage of alloying elements in chemical composition of steel. The data base used here involves a large variety of different steel types such as structural steels, stainless steels, rail steels, spring steels, high temperature creep resisting steels and tool steels. Scatter diagrams and mean relative error (MRE) statistical criteria are used to compare the performance of developed neural network with the results of Andrew′s empirical equations and a feed forward neural network with “gradient descent with momentum” training algorithm. The results showed that Bayesian regularization neural network has the best performance. Also, due to the satisfactory results of the developed neural network, it was used to investigate the effect of the chemical composition on Ac1 and Ac3 temperatures. Results are in accordance with materials science theories.
2014 Vol. 21 (2): 246-251 [
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252
Mohsen Askari-Paykani,Mehrdad Shayan,Morteza Shamanian
Weldability of Ferritic Ductile Cast Iron Using Full Factorial Design of Experiment
The weldability of a ferritic ductile cast iron was investigated as a function of different consumables and welding conditions. A 23 full factorial experimental design was used to analyze the effect of factors and their interactions on ultimate tensile strength of weldments. The shielded metal arc welding (SMAW) process was used with two types of consumables (E7018 and ENi-CI) under eight different conditions using as-cast samples. The microstructural evolution and fracture mechanisms were investigated by optical microscopy and scanning electron microscopy (SEM), respectively. The hardness, tensile and impact tests were also performed to determine the weld quality. Based on experiment design, preheat, consumable, cooling condition, preheat-cooling and preheat-consumable interactions were significant factors. Preheat is the most effective factor and in the case of E7018, preheat and cooling conditions were the most sensible factors. It was found that buttering was the most appropriate welding method for ferritic ductile cast iron.
2014 Vol. 21 (2): 252-263 [
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264
Jian-tao WANG,Wei HAN,He-li LUO,Shang-ping LI
Hot Deformation Behavior of Ni3Al-based Alloy MX246A
The hot deformation behavior of homogenized Ni3Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1150-1225 ℃ and strain rate range of 0001-01 s-1. Microstructural observation revealed striped secondary γ′ phase which was vertical to compression axis, and precipitation of fine ternary γ′ phase. The amount of striped secondary γ′ phase reduced and that of fine ternary γ′ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controlled by dynamic recovery mechanism.
2014 Vol. 21 (2): 264-268 [
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269
Ai-hua CHEN,Hai-rong GUO,Hua-long LI,Toshihiko EMI
Formation of Edge Crack in 14%Si Non-oriented Electrical Steel during Hot Rolling
Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 14%Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were found to be coarse as-cast microstructure, grain boundary oxidation in reheating furnace, lack of dynamic recrystallization during hot rolling and increase of temperature, resulting in reduced hot ductility in strip edge region. Countermeasures against the edge crack are proposed accordingly. Lowering reheating temperature and reducing holding time reduced oxidation and decarburization. Hot charging temperature was increased to decrease reheating temperature. And using an edger can refine microstructure in strip edge region. Finally, edge heater can be added to increase edge region formability by inducing dynamic recrystallization and ductility by increasing temperature.
2014 Vol. 21 (2): 269-274 [
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