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2016年, 第23卷, 第7期 刊出日期:2016-07-15
  

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    Metallurgy and Metal Working
  • Guo-hua ZHANG,Yu-lan ZHEN,Kuo-chih CHOU
    中国钢铁期刊网. 2016, 23(7): 633-637.
    摘要 ( )   可视化   收藏
    During the smelting process of the high Al steels, the reaction between SiO2 in molten slag and dissolved aluminum in liquid steel always takes place. This aluminathermic reduction reaction will lead to the substitution of 1 mol SiO2 for 2/3 mol Al2O3. Therefore, the investigations about the influence of the ratio of Al2O3 to SiO2 on viscosity and structure changes of mould flux during this process are very necessary. The viscosity variation of CaO-SiO2-Al2O3-CaF2 melts was studied by changing compositions considering the aluminathermic reduction reaction. It was found that viscosity increased monotonously with gradually increasing the substitution extent. According to the Raman analysis, the substitution of Al2O3 for SiO2 leads to the decrease of non-bridging oxygen but the increase of bridging oxygen. Therefore, degree of polymerization and viscosity increase as the substitution extent increases. By comparing the measured viscosities with the model calculated values, it was found that both the recently developed Zhang′s model and Roboud model could describe the viscosity variation behavior of CaO-SiO2-Al2O3-CaF2 melts very well.
  • Lin ZHANG,Ke HAN,Tian-nan MAN,En-gang WANG,Xiao-wei ZUO
    中国钢铁期刊网. 2016, 23(7): 638-646.
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    The effect of electromagnetic stirring (EMS) on microstructure and performance of Ag-8 mass%Ni composite was investigated under both solidified and deformed conditions. Without EMS, the Ag matrix formed short, thick dendrites in the ingot; whereas with EMS, dendrites were long and slim. Ni phase mainly formed particles or ribbons, distributed along boundaries between dendrite arms. Cold drawing of the solidified Ag-Ni ingots, both with and without EMS, produced high strength in-situ metal-matrix composite (MMC) consisting of Ag matrix reinforced by Ni ribbons. EMS improved the ductility of the composite, consequently enhancing its drawability and strength. EMS also increased the electrical conductivity in both solidified ingots and deformed in-situ composite wires. In both cases, hardness and tensile strength remained high. A model based on a combination of the modified linear rule of mixtures and the Hall-Petch relationship was used to rationalize the tensile strength and hardness with respect to its fabrication parameters and the microstructure of Ag-Ni in-situ composite.
  • ANG,,Yan-ping BAO,
    中国钢铁期刊网. 2016, 23(7): 647-654.
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    effects of some key factors on nitrogen absorption during the smelting process of X70 pipeline steel were studied, and the source of nitrogen pick-up was analyzed to find the bottleneck for nitrogen control. A series of measures were put forward to decrease the nitrogen pick-up. The results indicated that an exponential relationship existed between the nitrogen absorption index and the free oxygen in molten steel. Nitrogen absorption index could decrease below 03 when free oxygen in molten steel was above 100×10-6 after tapping. For low sulfur killed steel, the nitrogen absorption ratio and sulfur content satisfied a linear relationship with a slope of -0007. Low free-oxygen and sulfur were beneficial to the deep desulfurization during vacuum treatment. The contradiction of high desulfurization ratio and low nitrogen pick-up during LF process could be resolved by skimming oxidizing slag after tapping and making new high basicity top slag. After optimization, the average content of nitrogen in final product decreased from 46×10-6 to 35×10-6.
  • En-hui WU,,Rong ZHU,Shao-li YANG,Lan MA,Jun LI,Jing HOU
    中国钢铁期刊网. 2016, 23(7): 655-660.
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    The smelting-separation process for metallized pellets of vanadium-bearing titanomagnetite concentrates was studied. The influences of smelting temperature, smelting time, and the basicity of the metallized pellet on vanadium and iron recovery were investigated. The characteristics of titanium slag were analyzed using X-ray diffraction, energy dispersive spectroscopy, and mineralographic microscopic analysis. The results demonstrate that appropriate increases in smelting temperature and smelting time can improve the vanadium and iron recovery from metallized pellets and are beneficial for the slag-iron separation. Although increasing the basicity of the metallized pellet can considerably improve the vanadium and iron recovery, the TiO2 grade of titanium slag was decreased. Under the optimal conditions, 9017% of vanadium and 9298% of iron in the metallized pellet were recovered, and the TiO2 grade of titanium slag was 5501%. It was found that anosovite, augite, spinel, glassiness, and metallic iron were the main mineral phases of the titanium slag.
  • De-qing ZHU,Hao WANG,Jian PAN,Cong-cong YANG
    中国钢铁期刊网. 2016, 23(7): 661-668.
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    High pressure roll grinding (HPRG) and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate, which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores. The results indicated that when high-phosphorus iron ore concentrates containing 5492 mass% iron and 076 mass% phosphorus were directly processed through acid leaching, iron ore concentrates containing 5574 mass% iron and 033 mass% phosphorus with an iron recovery of 8464% and dephosphorization of 6379% were obtained. When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching, iron ore concentrates containing 5603 mass% iron and 021 mass% phosphorus with an iron recovery of 8565% and dephosphorization of 7749% were obtained. Meanwhile, when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching, iron ore concentrates containing 5802 mass% iron and 010 mass% phosphorus were obtained, with the iron recovery reaching 8842% and the dephosphorization rate reaching 8899%. Mechanistic studies demonstrated that ball milling can reduce the particle size, demonstrating a prominent reunion phenomenon. In contrast, HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals, which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate. As such, the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation, further strengthening the dephosphorization.
  • Yong-qin WANG,Zhi-fang LIU,Hen-gan OU,Yuan-xin LUO,Xing-chun YAN
    中国钢铁期刊网. 2016, 23(7): 669-676.
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    Leveling process plays an important role in delivering the desired material properties and product standards. An analytical method for the rotational leveling process of bars was presented. First, each cross section of the bar in the leveling area was discretized with the roller gap-curvature relations established in both planes XY and XZ. Second, a numerical procedure with two steps was developed to simulate both pressing and leveling processes. This approach can be easily implemented to produce simulation results of the curvature and trajectory distributions during the leveling process, as well as the bending and residual stresses. It is found that curvature and trajectory distributions follow a sine-shape due to the characteristic of rotational movement, which also results in a helical pattern of residual stress after leveling. Based on the results obtained, it is also observed that the rotational movement is beneficial for adding the number of bending cycle. This is the reason why there are only a few pairs of rollers on the bar leveler.
  • Material
  • Li-li MA,Ying-hui WEI,,Li-feng HOU,Chun-li GUO
    中国钢铁期刊网. 2016, 23(7): 677-684.
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    The fatigue performance and fracture mechanism of laser welded twinning induced plasticity (TWIP) steel joint were investigated experimentally based on the evolution of microstructure and micromechanical properties. The optical microscopy was used to analyze the evolution of microstructure. The variation of composition and phase structure of fusion zone were detected by energy dispersive X-ray and X-ray diffraction spectrometers. The micromechanical behaviors of the various zones were characterized using nanoindentation. The static tensile test and high cycle fatigue test were performed to evaluate the mechanical properties of welded joint and base metal. The microstructures, tensile properties and fatigue strength of base metal as well as welded metal were analyzed. The fatigue fracture surfaces of base metal and welded joint were observed by means of scanning electron microscopy, in order to identify fatigue crack initiation sites and propagation mechanisms. Moreover, the fatigue fracture characteristics and mechanisms for the laser welded TWIP steel joints were analyzed.
  • Zhi-xin XIA,Chuan-yang WANG,Chen LEI,Yun-ting LAI,Yan-fen ZHAO,Lu ZHANG
    中国钢铁期刊网. 2016, 23(7): 685-691.
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    The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied. The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy. Kinetic modeling was carried out using the software DICTRA. The results indicated Fe2(W,Mo) Laves phase has formed during creep with 200 MPa applied stress at 883 K for 243 h. The experimental results showed a good agreement with thermodynamic calculations. The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa, whereas, creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa. Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature. Microstructures at the vicinity of fracture surface, the gage portion and the threaded ends of creep rupture specimens were also observed, indicating that creep tensile stress enhances the coarsening of Laves phase.
  • Juan JIA,Wei-wei ZHU,Xin-li SONG,Ze-xi YUAN
    中国钢铁期刊网. 2016, 23(7): 692-698.
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    The precipitation behavior of FeTiP in interstitial free high strength (IFHS) steels has been studied by using a transmission electron microscope (TEM). The results show that the TiC particles, appearing at earlier stage, are more stable than the FeTiP ones during recrystallization annealing at the two given temperatures (810 ℃ and 840 ℃). Therefore, the FeTiP particles can only be observed in the steels with sufficient amount of Ti. There is a critical forming time for the FeTiP, which is between 90-120 s at 810 ℃ and 60-90 s at 840 ℃. The precipitation of FeTiP involves two steps, ie the formation of FeTi precursors and the diffusion of P. The former step determines the reliance of Ti content for the precipitation of FeTiP, whereas the latter step leads to the difference in the critical annealing time. interstitial free high strength steel; FeTiP precipitation; critical annealing; formation mechanism
  • Gang WANG,Ping XIAO,Zhong-jia HUANG,Ru-jie HE
    中国钢铁期刊网. 2016, 23(7): 699-704.
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    Fe-based powder with a composition of Fe4287Cr1598Mo1633C1594B888 (at%) was used to fabricate coatings by high-velocity oxygen fuel spraying. The effects of the spraying parameters on the microstructure and the wear properties of the Fe-based alloy coatings were systematically studied. The results showed that the obtained Fe-based coatings with a thickness of about 400 μm consisted of a large-volume amorphous phase and some nanocrystals. With increasing the fuel and oxygen flow rates, the porosity of the obtained coatings decreased. The coating deposited under optimized parameters exhibited the lowest porosity of 28%. The excellent wear resistance of this coating was attributed to the properties of the amorphous matrix and the presence of nanocrystals homogeneously distributed within the matrix. The wear mechanism of the coatings was discussed on the basis of observations of the worn surfaces.
  • Qing-mei JIANG,Xiao-qiang ZHANG,Li-qing CHEN
    中国钢铁期刊网. 2016, 23(7): 705-710.
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    Maximum hardness test in weld heat-affected zone (HAZ), oblique Y-groove cracking test and mechanical property test of welding joint of 1000 MPa grade ultra-low carbon bainitic steel were carried out, so as to research the weldability of the steel. The results show that the steel has lower cold cracking sensitivity, and preheating temperature of 100 ℃ can help completely eliminate cold cracks, generating good process weldability. The increase of preheating temperature can reduce the hardening degree of heat-affected zone. The strength of welding joint decreases and hardness reduces when heat inputs increase, and excellent mechanical properties can be obtained when low welding heat inputs are used. Fine lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.
  • Yan-guang CAO,Le XU,Gou-qiang ZHANG,Jie SHI,Mao-qiu WANG
    中国钢铁期刊网. 2016, 23(7): 711-716.
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    Rolling contact fatigue (RCF) properties of SAE 8620 steel after case carburizing have been investigated under two contact stresses of 40 and 55 GPa. Results show that the RCF life ranges from 25×106 to 3×107 cycles under the contact stress of 55 GPa, while it can be more than 1×108 cycles under the contact stress of 40 GPa. The rated fatigue life L10 (lives with the 10% failure) is also drastically shortened from 98×106 to 54×105 cycles when the contact stress is increased from 40 to 55 GPa. Theoretical calculations and fractographs show that the maximum shear stress and the contact area increase with increasing the contact stress, making RCF tend to occur earlier.
  • Zhao-yang CHENG,Jing LIU,Wen-si CHEN,Jia-chen ZHU,Xi-feng LIN,Zhi-dong XIANG
    中国钢铁期刊网. 2016, 23(7): 717-721.
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    The effect of adding 05 mass% Cu on ductility and magnetic properties of Fe-65Si (mass%) alloy was investigated. The alloys with and without 05 mass% Cu addition were warm rolled into thin sheets of thickness no more than 03 mm at temperature below 600 ℃. It was found that the alloy with 05 mass% Cu addition was more easily warm rolled than Cu-free alloy. Tensile tests were carried out to further investigate this phenomenon, which confirmed that the ductility of the alloy with 05 mass% Cu addition was significantly higher than that of Cu-free alloy at 550 ℃. Based on the results of transmission electron microscopy analysis, the ductility increase of the alloy with 05 mass% Cu addition was attributed to the effect of Cu on the promotion of dynamic recovery and suppression of long-range order in the alloy during warm rolling process. It was also observed that the iron loss was lower and inductance was higher for the alloy with 05 mass% Cu addition. Thus, it can be concluded that adding a suitably small amount of Cu would not only increase the ductility of Fe-65Si alloy at warm rolling temperatures but also improve its magnetic properties.
  • Muna A. ABU-DALO,Nathir A. F. AL-RAWASHDEH,Ahmed A. MUTLAQ
    中国钢铁期刊网. 2016, 23(7): 722-732.
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    The inhibition effect of lignin sulfonate against corrosion for mild steel in acidic solution has been examined by means of FTIR (fourier transform infrared spectroscopy), FAA (flame atomic absorption) spectroscopy, SEM (scanning electron microscope), EDS (energy dispersive X-ray spectroscopy), and mass loss techniques. The results revealed that lignin is a beneficial inhibitor for mild steel corrosion in acidic medium. It has been further found that Langmuir adsorption isotherm is obeyed by the tested lignin′s adsorption over the surface of mild steel. The range of inhibition efficiency (IE) in 2 mol·L-1 HCl was found to be 7588%-8788% for Reax 88A, 4072%-6032% for Reax 88B, and 5432%-6303% for Reax 100M, after immersed at 298 K for 24 h time.
  • Gh MOHAMMED,,S. EI-GAMAL,
    中国钢铁期刊网. 2016, 23(7): 733-738.
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    Effects of γ-irradiation and deformation temperature (T) on the tensile properties of Pb-2 mass% Sb alloys were studied. The samples were annealed at 458 K for 2 h in air, then water quenched after they were γ-irradiated (the different doses were 05, 10, 15, and 20 MGy). The tensile properties were performed using stress-strain measurements at a constant strain rate (12×10-3 s-1) and at different T (303-393 K). It was found that at constant dose, the fracture stress (σF) decreases while the fracture strain (εF) increases as T increases. At particular T, σF increases while εF decreases with increasing dose. The strain-hardening exponent (n), which is the slope of the relation between ln(σ) and ln(ε) of the parabolic part of the stress-strain curve, was determined and its values increase as T increases and decrease as the dose increases. The value of the activation energy increases as the dose increases from 007 eV for un-irradiated sample to 01 eV for the 2 MGy-irradiated sample. These values are in accordance with that needed for dislocation movement and ordering process. An interpretation of the results was given, based on the creation of point and line defects due to γ-irradiation, and that results in a distribution of beta phase (Sb-phase), leading to a difficulty in the movement of dislocations, so there is an increase in alloy hardness.