钢铁研究学报(英文版)
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2017 Vol. 24 No. 10
Published: 2017-10-15
979
Shan Ren*,Fu-qiang Guo,Qi Zhao,Jie Yang,Lu Yao,Ming Kong
Sintering flue gas desulfurization with different carbon materials modified by microwave irradiation
Modification of metallurgical coke, biomass char and semi-coke was carried out using a microwave device with power of 450-850 W and irradiation time of 6-12 min. The desulfurization rates of three carbon materials before and after modification were tested. The effects of microwave power and irradiation time on the pore texture and surface chemical characteristics of the three carbon materials were examined by SEM, BET and Fourier transform infrared spectroscopy (FTIR). The results showed that the specific surface area, total pore volume and pore diameter of biomass char and semi-coke after irradiation decreased slightly. Noteworthily, the pore diameter turned small and the acidic functional groups on their surface decomposed, thereby the basicity of carbon surface increased by microwave modification. The optimal promotion of desulfurization rate of three carbon materials was semi-coke irradiated at 850 W for 9 min and the sulfur dioxide adsorption rate was up to 45%.
2017 Vol. 24 (10): 979-984 [
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985
Tao Xu,Guang-wei Wang,*,Jian-liang Zhang,Teng-fei Song,Run-sheng Xu
Non-isothermal study of gasification process of coal char and biomass char in CO2 condition
Non-isothermal method was used to study gasification characteristics of three coal chars and one biomass char. Four chars were made from anthracite coal (A), bituminous coal (B), lignite coal (L), and wood refuse (W), respectively. The gasification process was studied by random pore model (RPM), unreacted core model (URCM) and volumetric model (VM). With an increase in metamorphic grade, the gasification reactivity of coal char decreased, and the gasification reactivity of biomass char was close to that of low metamorphic coal char. With an increase in heating rate, the gasification of all samples moved towards high temperature zone, and the whole gasification time decreased. It was concluded from kinetics analysis that the above-mentioned three models could be used to describe the gasification process of coal char, and the RPM fitted the best among the three models. In the RPM, the activation energies of gasification were 1939, 2253 and 2028 kJ/mol for anthracite coal char, bituminous coal char and lignite coal char, respectively. The gasification process of biomass char could be described by the URCM and VM, while the URCM performed better. The activation energy of gasification of wood refuse char calculated by the URCM was 2820 kJ/mol.
2017 Vol. 24 (10): 985-990 [
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991
Chao Geng,,Hua-jun Wang,*,Wen-tao Hu,Li Li,Cheng-shuai Shi
Recovery of iron and copper from copper tailings by coal-based direct reduction and magnetic separation
A technique comprising coal-based direct reduction followed by magnetic separation was presented to recover iron and copper from copper slag flotation tailings. Optimal process parameters, such as reductant and additive ratios, reduction temperature, and reduction time, were experimentally determined and found to be as follows: a limestone ratio of 25%, a bitumite ratio of 30%, and reduction roasting at 1473 K for 90 min. Under these conditions, copper-bearing iron powders (CIP) with an iron content of 9011% and copper content of 086%, indicating iron and copper recoveries of 8725% and 8344% respectively, were effectively obtained. Scanning electron microscopy and energy dispersive spectroscopy of the CIP revealed that some tiny copper particles were embedded in metal iron and some copper formed alloy with iron, which was difficult to achieve the separation of these two metals. Thus, the copper went into magnetic products by magnetic separation. Adding copper into the steel can produce weathering steel. Therefore, the CIP can be used as an inexpensive raw material for weathering steel.
2017 Vol. 24 (10): 991-997 [
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998
Wei Wang,,Ming Deng,,Run-sheng Xu,,Wei-bo Xu,,Ze-lin Ouyang,,Xiao-bo Huang,,Zheng-liang Xue,
Three-dimensional structure and micro-mechanical properties of iron ore sinter
A new analysis method based on serial sectioning and three-dimensional (3D) reconstruction was developed to characterize the mineral microstructure of iron ore sinter. Through the 3D reconstruction of two types of iron ore sinters, the morphology and distribution of minerals in three-dimensional space were analyzed, and the volume fraction of minerals in a 3D image was calculated based on their pixel points. In addition, the microhardness of minerals was measured with a Vickers hardness tester. Notably, different mineral compositions and distributions are obtained in these two sinters. The calcium ferrite in Sinter 1 is dendritic with many interconnected pores, and these grains are crisscrossed and interwoven; the calcium ferrite in Sinter 2 is strip shaped and interweaves with magnetite, silicate and columnar pores. The calculated mineral contents based on a two-dimensional region are clearly different among various layers. Quantitative analysis shows that Sinter 1 contains a greater amount of calcium ferrite and hematite, whereas Sinter 2 contains more magnetite and silicate. The microhardness of minerals from highest to lowest is hematite, calcium ferrite, magnetite and silicate. Thus, Sinter 1 has a greater tumbler strength than Sinter 2.
2017 Vol. 24 (10): 998-1006 [
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1007
Cong-cong Yang,,De-qing Zhu,Ben-jing Shi,Jian Pan,Li-ming Lu,Xiao-bo Li,Ya-ping Mo
Comparison of sintering performance of typical specular hematite ores with distinct size distributions
The sintering performance of three typical specular hematite ores (coarse SO-A, intermediate SO-B and ultrafine SO-C) was compared in an industrial ore blend through pilot-scale sinter pot tests. The effect of particle size of specular hematite ores on their granulation and sintering performance was revealed. Compared with the coarse SO-A fine and ultrafine SO-C concentrate, the intermediate SO-B showed inferior granulation and sintering performance characterized with poorer bed permeability and productivity, lower sinter strength and higher fuel rates. A new material preparation method was hence proposed and verified at both pilot and industrial scales. The proposed method by mixing SO-B with a high amount of goethite-type iron ore fines was found to be an effective way in improving the granulation and assimilative characteristics of ore blend comprising 31% intermediate SO-B, leading to improved sinter productivity and lowered fuel rates. The metallurgical properties and microstructure of sinters were also investigated. The sinters obtained through the proposed preparation method were generally stronger and more reducible on account of better sinter structure with more relict hematite ultimately connected with needle-like silico-ferrite of calcium and aluminum and lower porosity.
2017 Vol. 24 (10): 1007-1015 [
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1016
Xun-fu Wang,,Qi-jie Zhai
Corrosion mechanism research and microstructure analysis of Baosteel No3 blast furnace hearth
Baosteel No3 blast furnace hearth was divided into tuyere area, taphole area, taphole upper side wall and taphole lower side wall according to different working situations. Through chemical composition analysis, scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry and other means, chemical composition and microstructure of different parts of hearth carbon brick were analyzed and markedly different corrosion mechanisms of these areas were found. Zn element in form of ZnO mainly deposited on the hot side of carbon brick. There was no obvious evidence that Zn permeates into carbon bricks and erodes them. Except for taphole area, K, Na, and Fe contents from hot side to cold side gradually rise and fall, resulting in the decrease of apparent porosity, the increase of density and the higher thermal conductivity compared with those of new carbon brick. The higher content of Fe in carbon brick leads to more serious erosion because Fe has greatly changed the physical properties of carbon brick. In the taphole area, the contents of Si and Al present obvious concentration gradient because of the mechanical souring of molten iron and slag. The SiO2 and Al2O3 particles that have different expansion factors with carbon brick damaged the carbon substrate because of temperature fluctuation. The graphitized carbon found on H4 where is the most serious corrosion site means that the carbon brick ever directly contacts with molten iron.
2017 Vol. 24 (10): 1016-1022 [
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1023
Ting-feng Song,Xiao-song Jiang,Zhen-yi Shao,,De-feng Mo,De-gui Zhu,Min-hao Zhu,Christina H. Young,Zhi-ping Luo
Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys
Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature. Titanium alloy TC4 (Ti-6Al-4V) and 4J29 Kovar alloy (Fe-29Ni-17Co) were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min, under a pressure of 3466 MPa. Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction(XRD) and energy dispersive spectroscopy (EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis. Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength. Results of EDS and XRD indicated that (Fe, Co, Ni)-Ti, TiNi, Ti2Ni, TiNi2, Fe2Ti, Ti17Mn3 and Al6Ti19 were formed at the interface. When the bonding temperature was raised from 700 to 850°C, the voids of interface were reduced and intermetallic layers were widened. Maximum tensile strength of joints at 535 MPa was recorded by the sintering process at 850°C for 120 min. Fracture surface of the joint indicated brittle nature, and failure took place through interface of intermetallic compounds. Based on the mechanical properties and microstructure of the diffusion-bonded joints, diffusion mechanisms between Ti-6Al-4V titanium and Fe-29Ni-17Co Kovar alloys were analyzed in terms of elemental diffusion, nucleation and growth of grains, plastic deformation and formation of intermetallic compounds near the interface.
2017 Vol. 24 (10): 1023-1031 [
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1032
Zhi-feng Li,Yong-quan He,Guang-ming Cao,Jun-jian Tang,Xiang-jun Zhang,Zhen-yu Liu
Effects of Al contents on microstructure and properties of hot-dip Zn-Al alloy coatings on hydrogen reduced hot-rolled steel without acid pickling
A new hot-dip galvanizing method was employed on hot-rolled low carbon steel. The effects of Al contents on microstructure, micro-hardness and corrosion resistance of Zn-Al alloy coatings were systematically investigated. Phase composition, microstructure and element distribution in Zn-Al alloy coatings were analyzed using X-ray diffraction (XRD) and electron probe micro analysis (EPMA), respectively. It is found that Al content (06-60 wt%) in galvanizing zinc affects surface quality and adhesion between coatings and matrix in the newly developed method. In addition, with increasing Al content, micro-hardness significantly increased due to the increase in Zn-Al eutectoid phases. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) also revealed that increase in Al plays a noticeable role in improving the corrosion resistance of Zn-Al alloy coatings.
2017 Vol. 24 (10): 1032-1040 [
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1041
Lin-kai Guo,Lei Wang,Dong-hui Yang
Scaling laws and mechanical properties of nanoporous copper
Through molecular dynamics simulations, the mechanical behavior of nanoporous copper under impact loading was investigated with relative densities ranging from 7791% to 9836%, focusing on deformation mechanism, the scaling laws and influence of ligament sizes. Results show that the classical Gibson-Ashby′s scaling laws should be modified for prediction of both the Young′s modulus and yield stress. A proportional relationship is established between cell wall thickness and yield stress, and new modified scaling equations are built for nanoporous copper with consideration on both relative mass density and size effects of ligaments. The size effect can be explained by larger surface area/volume ratio of samples with thinner ligament size and limited dislocation source activation due to narrow space between larger numbers of voids.
2017 Vol. 24 (10): 1041-1047 [
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1048
Meng-xuan Guo,Kai-xiang Gao,Wu-rong Wang,Xi-cheng Wei
Microstructural evolution of Al-Si coating and its influence on high tempera-ture tribological behavior of ultra-high strength steel against H13 steel
Al-Si coated ultra-high strength steel (UHSS) has been commonly applied in hot stamping process. The influence of austenitizing temperature on microstructure of Al-Si coating of UHSS during hot stamping process and its tribological behavior against H13 steel under elevated temperature were simulatively investigated. The austenitizing temperature of Al-Si coated UHSS and its microstructual evolution were confirmed and analyzed by differential scanning calorimetry and scanning electron microscopy. A novel approach to tribological testing by replicating hot stamping process temperature history was presented. Results show that the hard and stable phases Fe2Al5+FeAl2 formed on Al-Si coating surface after exposure to 930°C for 5 min, which was found to be correlated to the tribological behavior of coating. The friction coefficient of coated steel was more stable and higher than that of uncoated one. The main wear mechanism of Al-Si coated UHSS was adhesion wear, while abrasive wear was dominant for the uncoated UHSS.
2017 Vol. 24 (10): 1048-1058 [
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1059
Zhen-xue Shi,Shi-zhong Liu,Xiao-dai Yue,Li-jie Hu,Wan-peng Yang,Xiao-guang Wang,Jia-rong Li
Effect of cellular recrystallization on tensile properties of a nickel-based single crystal superalloy containing Re and Ru
A nickel-based single crystal superalloy containing Re and Ru was cast in a directional solidification furnace. The single crystal specimens after standard heat treatment were grit blasted with different pressures and then heat treated at 1100°C for 4 h under vacuum condition. The evolution of recrystallized microstructure and its effect on the tensile properties at 850 and 980°C were investigated. After heat treatment, the cellular microstructure was observed, and the thickness of the cellular recrystallization zone increases with the increase in grit blasting pressure. The appearance of the cellular structure undermines the tensile properties. Both the tensile strength and elongation decrease with increasing the thickness of the cellular structure. The recrystallized grain boundaries can act as the channels for the crack initiation and propagation during tensile test. The low bearing capacity of recrystallized layers and the local stress concentration resulting from the notch effect of cracking were the main reasons for the decrease of tensile properties.
2017 Vol. 24 (10): 1059-1064 [
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1065
Feng-ming Song,Lin-xiu Du
Erosion corrosion of low-alloy wear-resistant steels in alkaline slurry
Erosion corrosion causes significant problems in various industrial environments through a synergistic effect which results in much greater weight loss than the sum of the weight losses in the individual processes. The erosion-corrosion behavior of three low-alloy steels was investigated in a simulated concrete slurry using the rotation method. The key influencing factors and mechanism of material degradation were analyzed. The experimental results indicate that the weight loss increases with the linear velocity according to a nearly exponential relationship (W=KVn), where n is 140-214. This weight loss is mainly caused by erosion in the alkaline slurry, and steels with higher tensile strengths show higher erosion-corrosion resistance. The formation of many platelets and ring cracks and their removal from the sample surface during erosion corrosion in the slurry are thought to constitute the mechanism responsible for this weight loss. These platelets and ring cracks are formed by solid particles striking the sample surface. Craters are initially produced and subsequently disappear as they grow and come in contact with each other. Fewer craters were observed on the surfaces of samples that exhibited higher weight loss. The surface of the material became work-hardened because of the effect of the particles striking and scratching, and a deformed layer was produced on the surface for steels of lower strengths, leading to deeper and more abundant gouges.
2017 Vol. 24 (10): 1065-1072 [
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钢铁研究学报(英文版)
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