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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 104 (2018), No. 5

  • Effect of Natural Gas Injection Point on Combustion and Gasification Efficiency of Pulverized Coal under Blast Furnace Condition

    pp. 243-252

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    DOI:10.2355/tetsutohagane.TETSU-2017-087

    The reduction of CO2 emission from the ironmaking process is important issue from the view of environmental problems typified by global warming in recent years. Low RAR (reducing agent rate) operation of the blast furnace is one of effective measures for reducing CO2 emission. Injection of HRA (hydrogenous reducing agents) from the tuyere (where is the lower part of blast furnace) is also effective measure. In this study, the influence of HRA injection point on combustion and gasification efficiency of pulverized coal (PC) in the case of simultaneous injection of HRA and PC from double-channel lance was examined by small scale combustion furnace and three-dimensional numerical simulation for improvement permeability in blast furnace. Combustion experimental conditions were in three cases, case1: injected HRA from outer side and PC from inner side of double-channel lance, case2: injected HRA from inner side and PC from outer side of double-channel lance and case3: injected HRA and PC premixed. As a result, the combustion and gasification efficiency was increase in the order of case3, case2 and case1. The rate of combustion and gasification of PC was investigated in case1. Not only the oxidation reaction was also accelerated CO2 and H2O gasification reaction in the case of simultaneous injection HRA and PC. A three-dimensional numerical simulation of the experimental furnace was conducted, we confirmed the increase of combustion temperature, the acceleration of oxygen consumption and gasification reaction as with the experimental results in the case of simultaneous injection HRA and PC.
  • Agglomeration of Return Fines of Sinter for Blast Furnace Raw Materials

    pp. 253-257

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    DOI:10.2355/tetsutohagane.TETSU-2017-092

    Return fines of sinter were agglomerated with binder material such as cement and fine powder of blast furnace slag in order to use the agglomerates as raw materials in blast furnace. Reduction tests of the agglomerates were carried out to investigate high temperature properties of the agglomerates. Then, the following findings were obtained. The agglomerates have lower RDI (RDI < 20%) than sinter because brittle sinter were bonded discretely by using soft materials as binder and size degradation during reduction was hindered. The agglomerates have high RI (DI > 70%) than sinter because abundance ratio of fine pore in the agglomerates were high. The agglomerates have equal to or more strength after reduction at 700 and 900 °C because solid phase sintering was promoted by added ultra fine powder of iron oxide. Therefore, the agglomerates of return fines of sinter have more excellent properties in permeability and reducibility than sinter for blast furnace raw materials, and this concept is effective for utilizing sinter fines for blast furnace raw materials in a high pulverized coal ratio and low coke ratio operation.
  • Effect of Crystallographic Texture on Anisotropy of Mechanical Properties in High Strength Martensitic Steel

    pp. 258-263

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    DOI:10.2355/tetsutohagane.TETSU-2017-093

    The thermomechanical controlled processing (TMCP) is widely applied for one of the effective processes to improve strength and toughness of steel plates. In actual application, anisotropies of mechanical properties arising from crystallographic texture which is grown up in controlled rolling process are important issues. In this study the effect of texture on anisotropies of mechanical properties by experimentally manufactured YP960 MPa class steel plate was investigated. Strength varied through plate thickness from surface to mid-thickness. At surface, strength in longitudinal direction was higher than that in transverse direction, in contrast, strength in transverse direction was higher than that in longitudinal direction at mid-thickness. The major components of texture at plate surface were {110}<111> and {112}<111>, whereas those at mid-thickness were {332}<113> and {211}~{311}<011>. It is considered that the texture of plate surface was formed by shear strain in austenite region, and, that of mid-thickness was grown up by compressive strain. Crystal plasticity analysis based on texture information of the specimen revealed that the anisotropies of mechanical properties were strongly affected by microstructure orientation.
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  • Reduction of Contact Resistance on Titanium Sheet Surfaces by Formation of Titanium Carbide and Nitride, and Its Stability in Sulfuric Acid Aqueous Solution

    pp. 264-273

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    DOI:10.2355/tetsutohagane.TETSU-2017-085

    Separators for solid polymer fuel cells must have a low contact resistance with the carbon paper and stability in a corrosive environment of sulfuric acid in the cell. The titanium surface is highly resistant to corrosion thanks to a passive film but has high contact resistance.In this study, titanium carbide or nitride as the electrical conductor was formed on the surface by annealing commercially pure titanium sheet. The contact resistances of these sheets were evaluated before and after a sulfuric acid aqueous solution exposure test, “pH4 at 80°C for 4 days”, briefly simulating the operating environment. In addition, the same evaluation test was conducted with a surface with TiC formed dipped in nitric acid to enhance the stability in a sulfuric acid solution.The initial contact resistance falls below 10 mΩ·cm2 by formation of TiC and TiN, Ti2N on sheet surface. However, the contact resistance rises to 100 or above after the exposure test because a large amount of TiO2 precipitates. This is probably because TiC and TiN are dissolved by sulfuric acid, generating TiO2.By contrast, dipping in nitric acid hardly raises the contact resistance from less than 10 even after the exposure test. It is considered from the results of surface analyses that Ti ion generated by partial dissolution of TiC is turned into TiO2 by the oxidizability of nitric acid, changing the surface structure covering TiC. It is considered that the newly formed TiO2 film enhanced stability in a sulfuric environment.
  • Effect of Cold Reduction on Microstructure and Mechanical Property of 5% Mn Steel

    pp. 274-283

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    DOI:10.2355/tetsutohagane.TETSU-2017-069

    Recently, medium Mn steel has been focused on as one of the promising candidates for third generation AHSS, due to it having an excellent TS-El relationship. Medium Mn steel can retain a lot of austenite by reheating to an (α+γ) intercritical temperature. Research on this material was performed on hot rolled steel sheet and cold rolled steel sheet, using the martensite as the starting microstructure.The effect of cold reduction on the microstructure and mechanical property after intercritical annealing was discussed by using 0.2C-2Si-5Mn steel with softened bainite structure at 575°C and the following results were obtained.(1) Hot rolling and intercritical annealed steel sheet showed a lath type structure of ferrite and retained austenite. On the other hand, cold rolling and intercritical annealed steel sheet showed a mixture of equiaxed ultrafine ferrite and retained austenite. The volume fraction of retained austenite increased as the intercritical annealing time increased. The increasing behavior was promoted by cold reduction. The maximum volume fraction of retained austenite was about 40%, and was obtained for the longest annealing time, 300 min, in all steels.(2) Excellent mechanical properties, for example, TS; 1217 MPa, UEl; 27.6%, TS×UEl; 33,592 MPa% were obtained for the steel intercritically annealed at 675°C for 30 min after 50% cold reduction. Hot rolled steel showed continuous yielding, while cold rolled steel exhibited about 7% yield point elongation.These results were almost accorded with the previously reported results whose initial microstructure was martensite.
  • Effect of Grain Size on the Yield Stress of Cold Worked Iron

    pp. 284-291

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    DOI:10.2355/tetsutohagane.TETSU-2017-091

    Effect of ferrite grain size on dislocation strengthening was investigated in low carbon steels (0.006%C-0.15%C) with various grain sizes from 1 to 100 μm. In specimens with slight deformation, dislocation density increases in proportion to the inverse of ferrite grain size. In the dislocation density range below 2×1014/m2, dislocation density increases linearly against deformation strain but it tends to level off due to the dynamic recovery of dislocations when dislocation density has exceeded it. On the other hand, tensile tests revealed that yield stress follows the Hall-Petch relation for as-annealed specimens but follows the Bailey-Hirsch relation for cold rolled specimens. This means that flow stress depends on only the dislocation density regardless of grain size. As a result, it was concluded that the introduction of dislocations has been promoted with decreasing ferrite grain size and this results in the increase of flow stress in the uniform deformation region.

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