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2015年, 第22卷, 第12期 刊出日期:2015-12-15
  

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    Metallurgy and Metal Working
  • Wen YANG,,Ying ZHANG,Lifeng ZHANG,,Haojian DUAN,Li WANG
    中国钢铁期刊网. 2015, 22(12): 1069-1077.
    摘要 ( )   可视化   收藏
    Population density function (PDF), which can eliminate the arbitrariness caused by the choice of the number and the size of bins compared to the wellused histograms, was introduced to analyze the amount of inclusions. The population evolution of oxide inclusions in forms of PDF in Tistabilized ultralow carbon steels after deoxidation during industrial RH refining and continuous casting processes was analyzed using an automated SEMEDS system. It was found that after deoxidation till the early stage of casting, the alumina inclusions exhibited a lognormal PDF distribution, and three factors including the existence of a large amount of alumina clusters, the generation of alumina from the reduction of AlTiO inclusions and the reoxidation of molten steel were estimated as the reasons. The shape parameter σ was high after deoxidation and then decreased after Ti treatment, indicating that in a short period after deoxidation, the size of alumina inclusions was widely distributed. After Ti treatment, the distribution of inclusion size was more concentrated. The scale parameter m decreased with time during the whole refining process, indicating that the proportion of large inclusions decreased during refining. Contrarily, the AlTiO inclusions presented a fractal PDF distribution except at the end of casting with fractal dimension D of 43, and the constant of proportionality C decreased with time during RH refining and increased during casting process. The reoxidation of steel by slag entrapped from ladle was considered as the reason for the lognormal PDF behavior of AlTiO inclusions at the end of casting.
  • Wenlong ZHAN,,Keng WU,Zhijun HE,Qihang LIU,Xiaojuan WU
    中国钢铁期刊网. 2015, 22(12): 1078-1084.
    摘要 ( )   可视化   收藏
    Fuel consumption in the COREX3000 process run in Baosteel is currently higher than the design index. Therefore, mass and heat balance equations for the COREX process were established using the basic principles included in the Rist operating diagram for blast furnace (BF) as a reference. Thermodynamic calculations were then used to modify the Rist operating diagram so that it was suitable for the COREX process. The modified Rist operating diagram was then applied for the evaluation of metallization rate (MR) and fuel structure to reduce the energy consumption in the COREX process. The modified Rist operating diagram for the shaft furnace (SF) provided a nearly ideal value for the restriction point W when the metallization rate was increased, while the point P on the operating line for the melter gasifier (MG) moved upward due to reduction in the heat required in hearth. The feasibility of reducing the energy consumption during the COREX process by changing the fuel structure was also demonstrated.
  • Xiangning MENG,Rengan LIN,Jie YANG,Xiaojing ZUO,Miaoyong ZHU
    中国钢铁期刊网. 2015, 22(12): 1085-1090.
    摘要 ( )   可视化   收藏
    The meniscus shell plays an important role in slab quality and process operation for continuously cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscillation and liquid steel flow to generate disturbance of casting. The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermophysical properties and flow rate of steel to shed light on the formation of initial defects. The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending. The formed crack may also expand and propagate due to the following secondary cooling and straightening behavior. The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the nonuniform thickness of solidifying shell. The interdendrite bridging is also likely to be formed to produce other internal defects, such as air hole and solute enrichment in the residual molten steel located in the bridging area.
  • Jifang XU,Lijuan SU,Dong CHEN,Jieyu ZHANG,Yao CHEN
    中国钢铁期刊网. 2015, 22(12): 1091-1097.
    摘要 ( )   可视化   收藏
    The viscosities for the selected CaOMgOSiO2 and CaOMgOAl2O3SiO2 slags were measured by rotating cylinder method in a wide temperature range from 1608 K to 1823 K. The effects of temperature, slag basicity and Al2O3 content were studied. The results indicated that the viscosity decreased with increasing the slag basicity at the same temperature. And the viscosities of the slag initially increased linearly with increasing Al2O3 content in the slags and then decreased as the Al2O3 content in the slags continued to increase. Al2O3 addition has a more significant effect on the viscosity than slag basicity in the selected slags. Based on the experimental data and the fraction of solid phases calculated by the thermodynamic software, the effect of solid phases on slag viscosity was evaluated. The results indicated that the relationship between the relative viscosity and the volume fraction of solid phases estimated from the slag composition can be reasonable by allowing the inverse maximum fraction of solid particles to vary.
  • Zhiguo LUO,,Heng ZHOU,,Tao ZHANG,,Yang YOU,,Haifeng LI,,Zongshu ZOU,
    中国钢铁期刊网. 2015, 22(12): 1098-1106.
    摘要 ( )   可视化   收藏
    Based on the principles of the discrete element method (DEM), a scaleddown model was established to analyze burden descending behavior, including asymmetric phenomena, throughout an entire COREX shaft furnace (SF). The applicability of the DEM model was validated by determining its accordance with a previous experiment. The effects of discharge rate and abnormal conditions on solid flow were described in terms of solid flow pattern and microscopic analysis. Results confirmed that the solid flow of the COREX SF can be divided into four different flow regions; the largest normal force exists at the top of the manmade dead zone, and the weak force network exists in the funnel flow region. The basic solid flow profile was identified as a clear Flat→U→W type. Increasing the discharge rate decreased the quasistagnant zone size, but did not affect the macroscopic motion of particles or the shape of patterns above the bustle. For asymmetric conditions, in which particles were discharged at different rates, the solid flow patterns were asymmetric. Under an abnormal condition where no particles were discharged from the left outlet, a sizeable stagnant zone was formed opposite to the working outlet, and “motionless” particles located in the left stagnant zone showed potential to increase the period of static contacts and sticking effect.
  • Xuling CHEN,Yunsong HUANG,Min GAN,Xiaohui FAN,Zhiyuan YU,Lishun YUAN
    中国钢铁期刊网. 2015, 22(12): 1107-1112.
    摘要 ( )   可视化   收藏
    The influence of H2O (g) content in circulating flue gas on sintering was studied by simulating the flue gas circulating sintering. The results show that the burning speed of solid fuel and the heat transfer rate during sintering process are improved when the H2O (g) content increases from 0 to 6%, which accelerates the sintering speed. However, when the H2O (g) content exceeds 6%, the overwet zone in sinter bed is thickened, which deteriorates the permeability of sintering bed. In addition, the magnetite content in sinter increases, while the acicular calcium ferrite content decreases. Accordingly, the sinter yield and tumble index decrease with excessive H2O (g) content. To guarantee the yield and quality of sinter, the favourable H2O (g) content in circulating flue gas should be controlled to be less than 6%.
  • Material
  • Jian YANG,Shengen ZHANG,Bo LIU,Dean PAN,Chunli WU,Alex A. VOLINSKY
    中国钢铁期刊网. 2015, 22(12): 1113-1117.
    摘要 ( )   可视化   收藏
    The effect of TiO2 addition to the stainless steel slag glassceramics was studied. Different mass percentages of TiO2 were added to four samples of the parent glass made from stainless steel slag and cullet. The temperatures of nucleation and crystallization were determined by differential scanning calorimetry (DSC). According to Xray diffraction (XRD) and scanning electron microscopy (SEM) analysis, adding TiO2 refined grains and restricted the formation of the akermanite phase by capturing Ca2+ to form the perovskite phase. Diopside was the main crystal phase of the glassceramics. The bending strength and Vickers hardness increased with the addition of TiO2. The optimal amount of TiO2 was 7 mass%, and the highest bending strength and Vickers hardness were 1446 MPa and 626 GPa, respectively.
  • Qiang LI,Yuexiu QIU,,Bo LI,Dongliang ZHAO,Deen SUN,Dehui LI
    中国钢铁期刊网. 2015, 22(12): 1118-1125.
    摘要 ( )   可视化   收藏
    CrAlVN coatings are of good intrinsic mechanical and tribological properties but lack of strength. Silicon can provide nitride coating high strength and excellent oxidation resistance. Logically, the combination of CrAlVN and Si should provide a good candidate for dry machining. The effect of silicon content on CrAlSiVN coating′s mechanical, tribological properties and oxidation resistance was investigated. The coatings were deposited on cemented tungsten carbide and Si wafer (100) substrates in an inline magnetron sputtering system. Grazing incidence Xray diffractometer, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, electron probe microanalyzer, Xray photoelectron spectroscopy and Auger electron spectroscopy were employed to characterize the microstructure and chemistry. Nanoindentation and ballondisc tribotester were used in characterization of the mechanical and tribological properties. Incorporating with silicon, the CrAlVN coating was strengthened (hardness: 212 GPa up to 387 GPa); even after 2 h exposure to 700 ℃ in air, the hardness still maintains at 110 GPa.
  • Silian CHEN,Jun HU,,Xiaodan ZHANG,Han DONG,Wenquan CAO
    中国钢铁期刊网. 2015, 22(12): 1126-1130.
    摘要 ( )   可视化   收藏
    A mediumMn steel (02C5Mn) was processed by intercritical annealing at different temperatures (625 ℃ and 650 ℃). An ultrafinegrained microduplex structure consisting of alternating austenite and ferrite laths was developed by austenite reverse transformation (ART) during intercritical annealing after forging and hot rolling. Ultrahigh ductility with a total elongation higher than 30% was achieved in the temperature range from -196 ℃ to 200 ℃, and high impact toughness no less than 200 J at -40 ℃ was obtained. Based on the analysis of microstructure and mechanical properties, it was found that the enhanced ductility was determined by the phase transformation effect of austenite (TRIP effect), while the delayed ductile to brittle transition was controlled by austenite stability.
  • Qingchun LI,Lijuan LI,Guowei CHANG,Qijie ZHAI
    中国钢铁期刊网. 2015, 22(12): 1131-1137.
    摘要 ( )   可视化   收藏
    Carbide precipitation and martensite transformation in Cr5 steel have been observed in situ by hightemperature confocal laserscanning microscopy. In this way, the influences of pulsed current and pulsed magnetic field complex pretreatment on carbide precipitation and martensite transformation during continuous cooling have been studied. The results show that the electropulsing complex pretreatment promotes the precipitation of M7C3type carbides at high temperature, increases the start and finish temperatures of martensite transformation, and extends the phase transformation time. Martensite prefers to nucleate in the austenite with less precipitation of carbides due to the chemically homogeneous distribution of solute atoms.
  • Zhengwei GU,,Mengmeng L,,Guanhan LU,,Xin LI,,Hong XU,
    中国钢铁期刊网. 2015, 22(12): 1138-1143.
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    An experimental apparatus with cooling system and pressureadjustment assembly for simulating quenching was constructed to investigate the effect of contact pressure on the microstructures and mechanical properties of hotstamping parts. Qualitative and quantitative analyses of the microstructures of the asquenched parts were conducted; moreover, hardness and tensile tests were performed to measure their mechanical properties. The results indicated that contact pressure during quenching strongly affected the structures and performances of hotstamping components. An excessive low contact pressure led to insufficient martensitic transformation. The critical contact pressure for complete martensitic transformation for 40 mm 22MnB5 steel was 04 MPa when the temperature of the coolant was 20 ℃. However, in consideration of the efficiency of practical production, a contact pressure higher than 125 MPa is recommended.
  • Guohui ZHU,Hongbing ZHOU,Qinyi LI,Qiwei CHEN,Hairong GU,Yonggang LIU
    中国钢铁期刊网. 2015, 22(12): 1144-1148.
    摘要 ( )   可视化   收藏
    A newly designed hotstamping steel alloyed by chromium (Cr) and manganese (Mn) without boron (B) addition was developed for automobile mass reduction. The experimental results showed the CrMn alloyed steel could be quenched to full martensite microstructure when the cooling rate was higher than 14 ℃/s. Yield strength, tensile strength and elongation of the experimental hot stamping part reached 1180 MPa, 1645 MPa and 84%, respectively. The experimental hot stamping part possessed higher tensile strength and elongation, compared with conventional hotstamping steel of 22MnB5. Furthermore, excellent processing flexibility would be obtained in this novel hotstamping steel because of its lower critical cooling rate and phase transformation temperature. The design of the composition and investigations of microstructure, mechanical properties and hotstamping processing were also studied.
  • Pengyan LU,Yu LIU,Huajie WU,,Gang LIU,Xiang MENG,Yang XU
    中国钢铁期刊网. 2015, 22(12): 1149-1155.
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    Fatigue performance of hotrolled ribbedsteel bar with the yield strength of 500 MPa (HRB500) was studied with bendrotating fatigue test at a stress ratio of R=-1. It is determined by staircase method that its fatigue strength for 107 cycles is 451 MPa, which is higher than that of common carbon structural steel. This should be attributed to the finegrain strengthening resulting from the high content of alloy element V and ThermoMechanical Control Process (TMCP). The SN curve function is also obtained by nonlinear regression with three parameters power function. The fatigue fractures of the specimen were further analyzed with Scanning Electron Microscopy (SEM) and Energy Disperse Spectroscopy (EDS) to study the fracture mechanism. Taking into account microstructure, hardness and cleanliness of the material, it implies that the fatigue fractures of HRB500 rebar all arise from surface substrates in which many brittle inclusions are contained, and that the fatigue crack propagation is principally based on the mechanism of quasicleavage fracture, because of the intracrystalline hard spots leading to stress concentration and thus to the cracks. Moreover, the transient breaking area exhibits microvoid coalescence of ductile fracture due to the existing abundant inclusions.
  • Jian KANG,Jun LI,Kunyu ZHAO,Xuan BAI,Qilong YONG,Jie SU
    中国钢铁期刊网. 2015, 22(12): 1156-1163.
    摘要 ( )   可视化   收藏
    The passivation behaviors of super martensitic stainless steels (SMSS) were studied by polarization curves at passive potential of -01 V and in various NaCl solutions, electrochemical impedance spectroscopy (EIS) and Xray photoelectron spectroscopy (XPS) analysis. Electrochemical test results showed that, in alkaline solutions, passivation region width was wider, passivation current was smaller, and polarization resistance was greater; thus, the passive film of SMSS in alkaline solutions had better passivation behaviors than that in acidic solutions. The polarization curve and EIS of samples SMSS1 and SMSS2 were also used to study which sample had better passivation behaviors. All results demonstrated that passive film structure of SMSS1 sample was more stable, and capacity of passive film was enhanced. The impact of alloying elements on the passive film (SMSS) passivation capability was also discussed by XPS depth profiling, and XPS depth profiling showed that the composition of the passive film was mainly composed of Feoxide and Croxide. So the passive film structures were mixed layers of Feoxide and Croxide. Fe oxidation product and Cr oxidation product would help to improve the protective property of passive film, which could promote the formation of a passive film structure more stably and densely.
  • Lei CAO,Zhongmin YANG,Ying CHEN,Huimin WANG,Xiaoli ZHAO
    中国钢铁期刊网. 2015, 22(12): 1164-1173.
    摘要 ( )   可视化   收藏
    The influences of nitrogen content and austenitization temperature on Nb(C,N) precipitation in niobium microalloyed steels were studied by different methods: optical microscopy, tensile tests, scanning electron microscopy, transmission electron microscopy, physicochemical phase analysis, and smallangle Xray scattering. The results show that the strength of the steel with high nitrogen content is slightly higher than that of the steel with low nitrogen content. The increase in the nitrogen content does not result in the increase in the amount of Nb(C,N) precipitates, which mainly depends on the niobium content in the steel. The mass fraction of smallsized Nb(C,N) precipitates (1-10 nm) in the steel with high nitrogen content is less than that in the steel with low nitrogen content. After austenitized at 1150 ℃, a number of large cuboidal and needleshaped particles are detected in the steel with high nitrogen content, whereas they dissolve after austenitized at 1200 ℃ and the Nb(C,N) precipitates become finer in both steels. Furthermore, the results also show that part of the nitrogen in steel involves the formation of alloyed cementite.