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

Tetsu-to-Hagané Vol. 94 (2008), No. 7

  • Microstructure of Iron Dispersing Al2O3 Particle Reduced from (Fe,Al)2O3 by CO–CO2 Gaseous

    pp. 231-237

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    DOI:10.2355/tetsutohagane.94.231

    Carbon monoxide reduction of (Fe,Al)2O3 was carried out in order to clarify the possibility for ODS to be made by selective reduction of solid solution. The microstructure of reduction product was observed with XRD, SEM and EDS. The results are summarized as follows.
    The precipitate particle of about 100 nm was observed in iron reduced by 97%CO–3%CO2 at 1273–1373 K and was identified as κ′-Al2O3. On the other hand, the precipitate particle was Fe(Fe,Al)2O4 of spinel structure by using low reducing potential gas of 80%CO–20%CO2. The size of their particle was more than 200 nm.
    And then, the sequential reduction of (Fe,Al)2O3 by various CO–CO2 ratios at 1273 K was carried out to investigate the structure transformation of products during CO reduction.
    Solid solution of (Fe,Al)2O3 was reduced to solid solution of Fe3O4(FeOAl2O3). When the iron oxide was reduced to ‘FeO’, the Fe3O4(FeOAl2O3) was transformed to ‘FeO’ and Fe(Fe,Al)2O4 of spinel structure with the irregular shape. The solubility of Al2O3 in ‘FeO’ was less than 1%. It seemed that the size of Al2O3 particle in reduced iron depends on the that of Fe(Fe,Al)2O4 particle in FeO, which was affected by reducing potential.
  • Condition of Low-density Particle Entrainment into a Bath under Mechanical Agitation with an Immersion Cylinder

    pp. 238-243

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    DOI:10.2355/tetsutohagane.94.238

    Entrainment of small poorly-wetted particles into a bath agitated mechanically with an impeller is investigated based on water model experiments. The particles are found to be effectively entrained and then dispersed into the bath when a circular cylinder is immersed slightly from an offset radial position in the bath. The critical condition under which the particles are completely dispersed into the bath is clarified in this study. An empirical equation is derived for the critical condition as a function of the bath diameter, bath depth, impeller position, cylinder diameter, and so on. The applicable range of the equation is also presented.
  • Influence of the Iron Oxide Layer on Lubricating Properties in Seamless Pipe Hot Rolling

    pp. 244-250

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    DOI:10.2355/tetsutohagane.94.244

    It is well known that an iron oxide layer formed on a surface of work piece plays an important role of lubricating properties in hot rolling. However, a few papers fully reported the influence of the iron oxide layer on lubricating properties. Therefore, we investigated the influence of compositions and thickness of the iron oxide layer on lubricity by means of a simulation test of semless pipe hot rolling.
    First, some iron-oxide layers of various compositions and thickness were formed on three different steel materials by oxidizing treatment under different conditions: where the work pieces were exposed to air until the oxide layer grew to the set thickness. Then, the hot work piece was rolled between a cylindrical roll and a flat tool lubricated with graphite-based lubricant. The friction coefficient was measured during rolling, and the flat tool surface was observed after rolling.
    Summaries of the results are shown below.
    ① In case the rolled material was carbon steel, scoring didn't occur regardless of its elongation in the test condition. On the other hand, in case the rolled material was 10% Cr steel or 18%Cr–8%Ni stainless steel, scoring occurred when the elongation was high.
    ② The abovementioned results are thought to be caused that the scale of FeO generated in the case of carbon steel has high plasticity at elevated temperature.
  • Interface Separation Phenomenon in Ti–20mol%Al Alloy/Iron Material Joints

    pp. 251-257

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    DOI:10.2355/tetsutohagane.94.251

    Ti–20mol%Al (Ti–20Al, i.e. Ti–12.3mass%Al) alloy was diffusion-bonded to eutectoid steel at 1273 K for 3.6 ks in a vacuum. The joint had a space of a few micrometers in thickness between the Ti–20Al alloy and the steel, and several specimens separated near the interface promptly after the bonding treatment. This phenomenon, which is referred to as “interface separation”, is known to depend on alloy composition, bonding temperature and holding time. This paper describes the influence of carbon content in iron materials on the interface separation. Four kinds of carbon steels, an alloy steel and a cast iron were used as a mating material for the Ti–20Al alloy. Diffusion bonding was carried out at 1273K for 3.6 ks in a vacuum. The diffusion of constituent elements into each parent material and the formation of reaction phases were observed in the vicinity of the interface in all cases. The interface separation was clearly seen in the joints with the carbon steels and the cast iron containing more than 0.82 mass% C. It was also confirmed that the space formed near the interface spread to the iron material side. On the other hand, the bonding of the Ti–20Al alloy to the alloy steel with high carbon content was achieved without incident. In this joint, the diffusion of Fe into the Ti–20Al side was inhibited by TiC layer formed at the interface. The mechanism of the interface separation is discussed from the viewpoint of thermal stress, reaction phase and diffusion behavior.
  • Alloy Layer Formation and Abrasive Wear Property of High Temperature Aluminized Stainless Steels

    pp. 258-264

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    DOI:10.2355/tetsutohagane.94.258

    To clarify the formation of the alloy layers formed on stainless steels during high temperature aluminizing at 900°C in air and the wear properties of the aluminized stainless steels, the abrasive wear tests for 18Cr–8Ni steel, 16Cr steel and 13Cr steel were performed. Observed voids in the alloy layers of stainless steels were less than that of carbon steel. The thicknesses of alloy layers formed during high temperature aluminizing were large in the order of 13Cr steel, 16Cr steel and 18Cr–8Ni steel. The alloy layers of stainless steels aluminized at 900°C for 3 h were consisted of four layers. The FeAl layer tended to have the highest abrasive wear resistance in four layers. The abrasive wear resistance of this layer tended to increase as the content of Cr increased. The abrasive wear resistance of the alloy layers, having the hardness HV <300, increased linearly with increase of hardness. However the abrasive wear resistance of the alloy layers, having the hardness HV >500, tended to decrease as the hardness increases because of the brittle fracture of the alloy layers.
  • Relative Sensitivity Factor for Various Matrices Using Argon/Glow Discharge Mass Spectrometry

    pp. 265-269

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    DOI:10.2355/tetsutohagane.94.265

    Unification of relative sensitivity factors (RSFs) in Ar glow discharge mass spectrometry was investigated. A Mega flat cell was used as a discharge cell for disk samples; ultra-high purity Ar (99.9999%) was used as the discharge gas. A sample mask for the disk sample with an inner diameter of 12 mm (made by Ta: part of the anode) was used, and a donut-shaped alumina (Al2O3) piece with an inner diameter of 20 mm was used for insulation between the sample and the anode. Discharge parameters were set as 1 kV–3 mA. Reference materials, such as Al, Co, Ni, Ti, Cu, and Fe matrices, were measured; the RSF value of every element for each matrix was determined. Then the RSF values were recalculated using Fe as the internal standard element, and the possibility of unification was verified for each matrix. Results showed that the RSF values of elements analyzed for each matrix normalized by Fe agreed well for five kinds of matrices. The relative standard deviation (RSD (%)) of the average of those RSFs varied: from greater, 15% for W and 18% for Cu; to smaller, 6% for Si and 5% for Cr. Results therefore demonstrated that using the RSF value for Fe can enable quantitative analysis within 10% of relative error of materials and substances for which no reference material (group) is available. For example, Si and Si-based materials and substances can be analyzed by normalizing the RSF value of Si to 1, recalculating the RSF values of the element analyzed therewith, and using them for corrective quantitative analysis.

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