Tetsu-to-Hagané
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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 93 (2007), No. 1

  • Characteristics of Adhesion and Removal of Suspended Particle in Liquid by Bubble

    pp. 1-8

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    DOI:10.2355/tetsutohagane.93.1

    Gas injection is generally practiced in refining processes for metallurgy. The expectances for the gas injection involve the homogenization of bath temperature and compositions, and removal of second phase and dissolved impurities from molten metals.
    It is widely recognized that inclusions in steel cause defects to the products. Therefore, it is important to remove inclusions from liquid steel. Solid inclusions such as alumina and silica are not wetted by the liquid steel and can be removed by attachment to gas bubbles. The attachment and removal by bubble flotation is expected as one of promising techniques on inclusion removal in liquid steel. The aim of the present work is to investigate the effects of some factors such as particle diameter, agitation speed and particle contact angle to removal rate. In this study, water model experiments have been done under turbulent flow condition using a mechanically agitated vessel. It was confirmed that the removal rate of suspended particles in liquid shows first order kinetics until 4 min in the initial stage. Furthermore, it was found that the collision frequency function has decreased with increasing agitation speed and with decreasing contact angle.
  • The Post-reaction Strength of Catalyst-doped Highly Reactive Coke

    pp. 9-17

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    DOI:10.2355/tetsutohagane.93.9

    The development of production and utilization technology of highly reactive coke is significant in order to improve blast furnace reaction efficiency. In this report, the post-reaction strength of catalyst-doped highly reactive coke was investigated. The reaction between coke and CO2 was stopped at the weight loss of 20% and the reaction temperature was adjusted so that the reaction lasted for a constant period. In this experimental condition, the reaction temperature of highly reactive coke was lower than that of normal coke, which corresponds to the decrease in the thermal rezerve zone temperature in blast furnace. First, a decrease in reaction temperature made the reaction of the catalyst doped nut coke more homogeneous, which increased the post-reaction strength of the highly reactive coke produced by post-addition of catalyst to coke method, however, decreased that of the highly reactive coke produced by pre-addition of catalyst to coke method. Secondly, the post-reaction strength of catalyst-doped highly reactive coke produced by post-addition of catalyst to coke method became equal to or greater than that of normal coke. The kinds of catalysts and the catalyst adding method affects the porosity distribution of coke after reaction and hence the post-reaction strength of coke to a great extent. Suitable selection of catalysts and its addition method to coke leads to the highly reactive coke with post-reaction strength greater than that of normal coke. Catalyst-doped highly reactive coke seems to be promising to improve blast furnace reaction efficiency.
  • Effects of Atmospheric Gas Composition and Temperature on the Gasification of Coal in Hot Briquetting Carbon Composite Iron Ore

    pp. 18-22

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    DOI:10.2355/tetsutohagane.93.18

    The gasification behavior of carbon composite iron ore produced by hot briquetting process was examined under various gas atmospheres such as CO-N2, CO2-N2 and CO-CO2 at various temperatures. The gasification of coal was affected strongly by atmospheric gas concentration and reaction temperature. Kinetic analysis in various gas atmospheres was carried out by using the first order reaction model, which yields the straight line relation between reaction rate constants for the gasification of coal and the gas concentration. Therefore, reaction rate constants for the gasification of coal in CO-CO2-N2 gas atmosphere were written as follows;
    kC1=a×kC1(CO)+b×kC1(CO2)+c×kC1(N2)
    kC2=a×kC2(CO)+b×kC2(CO2)+c×kC2(N2)
    a=CCO/(CCO+CCO2+CN2), b=CCO2/(CCO+CCO2+CN2), c=CN2/(CCO+CCO2+CN2)
    where, kC1 and kC2 are the gasification rate constant of the first half (1/s) and the latter half (1/s) respectively, kC1(CO), kC1(CO2) and kC1(N2) are kC1 in 100% CO gas atmosphere (1/s), 100% CO2 gas atmosphere (1/s) and 100% N2 gas atmosphere (1/s) respectively, kC2(CO), kC2(CO2) and kC2(N2) are kC2 in 100% CO gas atmosphere (1/s), 100% CO2 gas atmosphere (1/s) and 100% N2 gas atmosphere (1/s) respectively, CCO, CCO2 and CN2 are the concentration of CO gas (vol%), CO2 gas (vol%) and N2 gas (vol%) respectively.
  • Grain Refinement and High-temperature Deformation Behaviour of Sub-zero Worked and Annealed SUS316L

    pp. 23-26

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    DOI:10.2355/tetsutohagane.93.23

    Strain-induced martensitic transformation followed by reverse transformation is a possible process to achieve the grain refinement necessary for the superplasticity in austenitic stainless steel SUS304. This process is expected to be applicable also to SUS316L in which working at lower temperature is required for the strain-induced transformation. In this study, the transformation behavior of SUS316L during sub-zero working and annealing was investigated. The grain size of about 1 μm was obtained by the process of 90% sub-zero rolling at liquid nitrogen temperature followed by annealing at 973K for 3600 s. Furthermore, this process condition provided the total elongation of more than 300% and the strain-rate sensitivity index (m value) of 0.3 in the strain rate range from 1.8 to 3.2×10-4/s.
  • In-situ Observation of Nucleation and Growth of Acicular Ferrite in Weld Metal

    pp. 27-32

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    DOI:10.2355/tetsutohagane.93.27

    Acicular ferrite is regarded as being the most desirable microstructural feature, from the strength and toughness point of view, in mild and low alloy steel weld metals. Recent evolution and diversity of mechanical property for base metal demand the same property to the weld. Thus, the understanding of the formation mechanism of acicular ferrite microstructure in weld is one of the essential issues for low alloy steel welds.
    We have suggested that high-temperature laser scanning confocal microscopy was suitable system to make clear the nucleation site of precipitate in rapid cooling process, such as welding. In the present work, the morphological development of acicular ferrite, was in-situ observed during weld cooling. The sample designed to form acicular ferrite microstructure was heated and cooled in infrared imaging furnace and the morphological developments were directly observed using laser scanning conforcal microscopy.
    The nucleation and growth at inclusion, sympathetic nucleation and impingement events of acicular ferrite were directly shown in high-time resolution.
  • X-ray and Nanoindentation Analyses on Plastic Deformation of Galvannealed Coating

    pp. 33-38

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    DOI:10.2355/tetsutohagane.93.33

    Using galvannealed steels rolled at various temperatures (∼100°C) and to various reductions (∼50%), plastic deformation in galvannealed coating layer was evaluated by scanning electron microscopy, X-ray diffraction for measuring half width value of diffraction peaks, and nanoindentation test. By rolling deformation, the thickness of the coating layer plastically decreased and its reduction became more remarkable at high temperature deformation, suggesting that macroscopic plastic deformation takes place in the coating layer. The plastic strain evaluated by X-ray diffraction parabolically increased with increasing rolling reduction in both layers of δ1 phase and Γ phase, but more significant in δ1 phase than in Γ phase. The F-h curves drawn by nanoindentation test indicate that the plastic deformation is more significant in order, α-Fe substrate>δ1 phase>Γ phase. Also, Vickers hardness results obtained by nanoindentation test showed that hardness is higher in order, Γ phase>δ1 phase>α-Fe substrate. Consequently, the Vickers hardness of each phase in the coating layer evaluated by nanoindentation was irreversibly correlated well with the plastic deformability of each phase in the coating layer evaluated by F-h curves and X-ray diffraction.
  • Codeposition Behavior of Impurity during Electrogalvanizing in Sulfate Bath in the Presence of Fe Ions

    pp. 39-43

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    DOI:10.2355/tetsutohagane.93.39

    The codeposition behavior of impurity Fe with Zn was investigated galvanostatically over the current density range from 1 to 1000 A/m2 at 40°C in zinc sulfate solution of pH 3 containing 5000 ppm of Fe2+ and the other organic or inorganic impurity. Fe hardly codeposited with Zn in the solution containing both Fe and Mo or Ni as impurity. The codeposition of Fe seems to be strongly suppressed in the presence of Zn2+ ions due to the adsorption of Zn hydroxide preferentially formed on the cathode. However, in the solution containing Fe and Cu, Fe evidently codeposited with Zn. The Fe content in deposit decreased with increasing the current density. The role of codeposited Cu is considered to promote Fe deposition by providing an active sites free from adsorbed Zn hydroxide. On the other hand, in the solution containing Fe and stearyle benzyl ammonium chloride (C18-Benzyl) as impurities, the codeposition of Fe was significantly recognized. The cathode potential for Zn deposition was greatly polarized by addition of C18-Benzyl and the Fe content in deposit increased with increasing the current density.
  • The Effect of Carbon Activity and Base Gas Compositions for Carbonitriding of SUJ2 Steel

    pp. 44-48

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    DOI:10.2355/tetsutohagane.93.44

    We have been investigating the nitrogen penetration mechanism into high carbon chromium bearing steel JIS-SUJ2 on carbonitriding processes. In the course of carbonitriding experiments under various conditions and EPMA analyses, the influences of carbon activity and base gas components on nitrogen penetration behavior were examined. As a result, the nitrogen penetration content of steel increased with the decrease of carbon activity and H2 partial pressure, and with the increase of undecomposed NH3 partial pressure. While, the partial pressures of CO and N2 had almost no effect.
  • Stabilization in Strength of Hot-rolled Sheet Steel Strengthened by Nanometer-sized Carbides

    pp. 49-56

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    DOI:10.2355/tetsutohagane.93.49

    Stable precipitation-strength of hot-rolled sheet steel can be realized with precipitates remaining fine even at high temperature coiling. This study deals with a relationship between the strength of ferritic steels strengthened by nanometer-sized carbides and coiling temperature in order to evaluate the stability of the strength against a deviation of coiling temperature. Ti-Mo-bearing and Ti-bearing steels were heat-treated for the precipitation of (Ti, Mo)C and TiC in ferrite matrix, respectively. These steels were hot-rolled and coiled in the temperature range from 550°C to 700°C. Matrix of the steels coiled at temperatures more than 600°C was only ferrite and nanometer-sized carbides in law were generated in the matrix. Ti-Mo-bearing steel exhibited high strength even at the high coiling temperature while the strength of Ti-bearing steel significantly decreased. Hardness of Ti-bearing steel just transformed at 650°C was the same as that at 625°C. In addition, while hardness of Ti-bearing steel coiled at 625°C significantly decreased during holding at 650°C for 86.4 ks, Ti-Mo-bearing steel did not show a large change in hardness. These results confirm that (Ti, Mo)C is not coarsened easily by Ostwald ripening at the high coiling temperature unlike TiC. Interfacial energy between (Ti, Mo)C and ferrite matrix can be the same as that in case of TiC since both carbides have the same structure and the equivalent lattice parameter. The retardation of Ostwald ripening of (Ti, Mo)C is attributed to a small amount of titanium in solution in Ti-Mo-bearing steel.
  • Evaluation of Antibacterial Ability of Some Pure Metals

    pp. 57-65

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    DOI:10.2355/tetsutohagane.93.57

    The biohazard in the medical treatment or the food industry sometimes is a matter of serious concern. Recently, the corrosion or degradation due to microbial activity is also coming to consider as one of significant problems in the industrial technology. In these biohazards, the proliferation and colonization of microbes on the material surfaces is recognized as the precursor. From a point of view of this point, the utilization of antibacterial material is considered as one of effective approach to control the activation of harmful microbes and to create a hygiene life space. Although there are so many commercial products with antibacterial ability, they are generally plastics, clothing fivers or ceramics. While, antibacterial metals (commercial products of metals with antibacterial ability) are not so popular as former. Moreover, there are some researches for antibacterial ability of silver or copper metal, the substance which is more paid attention as antibacterial agent is organic substances rather than inorganic ones. In this study, the interaction of some pure metals and microbes was examined by two experimental methods, the film contact method and the shaking flask method. Through these experiments, we evaluated the anti-bacterial ability of some pure metals and investigated the possibility of utilization for alloy element.
  • Accounting for Steel Stock in Japan

    pp. 66-70

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    DOI:10.2355/tetsutohagane.93.66

    During the last two decades, the total material input in Japan has been about 2 billion tons, and approximately 50%, i.e., about 1 billion tons has accumulated as the net addition to stock in the form of buildings, social infrastructure, and various kinds of products. The amount of the net addition to stock is calculated annually from the differential between the input and the output. Therefore, the contents of the accumulated stock are unknown. It is said that these unknown contents include material that has already been discarded as invisible waste. In this study, dynamic material flow analysis was conducted to quantify the amount of stock that is not associated with social activities and cannot possibly be collected as scrap in the future. First, we defined some terms: in-use stock, hibernating stock, and overall stock. Hibernating stock comprises the steel used for the constructional material of landfill site, the steel dissipated by corrosion and erosion, etc. Furthermore, we defined the system boundary to account for the steel stock and constructed equations to calculate the three types of stock. To calculate the amount of in-use stock, a dynamic model—the population balance model—was adopted. The amounts of in-use stock and hibernating stock in Japan from 1980 to 2000 were calculated. The result shows that 0.96 billion tons of the in-use stock is included in the 1.22 billion tons of overall stock in the year 2000.

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