ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 30 (1990), No. 11

  • Research and Development of Iron-based Alloys for Nuclear Technology

    pp. 905-916

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    DOI:10.2355/isijinternational.30.905

    This paper describes several of the nuclear materials research and development programs that have involved ferrous metallurgy. The research programs high-lighted are as follows: For light water reactors, corrections have been made for corrosion of coolant piping and irradiation embrittlement of pressure vessel steels. Gas-cooled reactor concerns have included breakaway oxidation of mild steel components, nitrided nitride strengthened cladding materials development, breakaway oxidation in martensitic steel and structural materials specifications for very high temperature. Programs on liquid metal reactors have included efforts on void swelling resistance, piping alloy optimization, and application of mechanically alloyed oxide dispersion strengthened steels. Fusion alloy development has considered first wall materials optimization and low activation materials development. Descriptions of the causes and needed corrections are given for each of these research and development programs.
  • Recent Research and Development of Reduced Activation Ferrous Materials in Japan

    pp. 917-926

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    DOI:10.2355/isijinternational.30.917

    The outline of research and development of reduced activation ferrous materials, today in Japan, is reviewed. Reduced activation ferrous materials are considered to be utilized for the first wall materials of fusion reactor. The concept of reduced activation materials is closely related to the waste management and reactor safety. The decay behavior of induced radioactivity shows that the substitution of Mn for Ni and that of W for Mo in ferrous materials are very effective to achieve a reduced level of long-term radioactivity. The efforts are being devoted to the development of ferritic 9Cr-W steels, austenitic Mn-Cr steels and Mn-Cr-W steels as candidate alloys, instead of 9Cr-Mo steels and modified type 316 stainless steels. Some results are presented to the toughness before and after neutron irradiation and creep rupture strength of 9Cr-W steels, and on the characteristics of sigma phase formation, high-temperature strength, and void swelling of austenitic Mn-Cr steels and Mn-Cr-W steels. Preferable chemical compositions for reduced activation ferrous materials are suggested.
  • Equilibrium Phase Diagram of Fe-Cr-Mn Ternary System

    pp. 927-936

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    DOI:10.2355/isijinternational.30.927

    The isothermal phase diagram of Fe-Cr-Mn ternary system at 923 K was investigated by means of a metallographic observation, conventional X-ray diffraction and an electron probe X-ray microanalysis. In particular, attention was directed towards the phase stability of the austenite (γ) phase.
    The σ phase was detected even in the alloy containing 6% Cr, indicating that the γ/γ+σ phase boundary at 923 K located in the lower Cr content region of the ternary system. The γ/γ+σ phase boundary determined experimentally in low Mn alloys (up to 20 wt% Mn), was consistent with the prediction using a critical [md.gif] value of 0.89, the value chosen following our previous experiments. Here, [md.gif] is the compositional average of the Md value which is the d-orbital energy level of transition metals calculated by a molecular orbital methods. On the other hand, the γ/γ+α-Mn phase boundary appeared in the more Mn-rich alloys and moved towards the lower Mn-content region with increasing Cr content. As the result, the γ single-phase region became rather narrow. It was concluded from these results that the γ single-phase region in Fe-Cr-Mn ternary system was not so broad as was reported previously.
  • Effects of Ta and Nb on Microstructures and Mechanical Properties of Low Activation Ferritic 9Cr-2W-0.2V Steel for Fusion Reactor

    pp. 937-946

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    DOI:10.2355/isijinternational.30.937

    In order to develop low activation high chromium ferritic steels for fusion reactors, the effects of 0.05-0.16 wt% Ta and 0.05 wt% Nb alloyings, and heat treatments on elevated temperature strength, toughness and microstructures of 0.1C-9Cr-2W-0.2V-0.04N steels were investigated. Normalizing and tempering conditions were determined as heating at 1050°C for 30 min and at 800°C for 1 h through observing the dissolution of carbonitrides of Ta and As temperatures, respectively. The optimum amount of Ta in consideration of creep-rupture strength and toughness was approximately 0.10 wt%. Delta-ferrite formed in 0.16 wt% Ta steel of which Cr-equivalent was approximately 10 wt%.The steels alloyed with Ta showed only slightly lower creep-rupture strength than that of the steel alloyed with the optimum amount of Nb, 0.05 wt%. Toughness of the steels alloyed with Ta was superior to that of the steel alloyed with Nb. Hence, Ta-addition can be recommended over Nb-addition in view of the improved toughness.
  • Mechanical Properties and Microstructure Changes of Low-activation 3Cr-2W-V-Ti Ferritic Steels Developed for Nuclear Applications

    pp. 947-954

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    DOI:10.2355/isijinternational.30.947

    The effects of alloying elements such as Cr, W, V and Mn on tensile strength at elevated temperatures, creep-rupture properties and toughness of low activation (2.25-3)Cr-(2-2.5)W-V-Ti steels were investigated together with their microstructure change during high temperature exposure. These steels were normalized to produce bainitic structures in the same manner as that for a conventional 2.25Cr-1Mo steel. They presented superior tensile strength at elevated temperatures and creep-rupture strength in comparison with a conventional 2.25Cr-1Mo steel. The creep-rupture strength of the steels at 500°C for 100000 h demonstrated about twice that of the conventional 2.25Cr-1Mo steel. The 3Cr-2.5W-0.2V-0.01Ti steel is recommended as a potential low activation ferritic steel for nuclear applications with well optimized mechanical properties, such as tensile strength at elevated temperatures, creep-rupture strength and toughness. The effects of alloying elements were discussed with correlating microstructural and mechanical aspects.
  • Cold Model Study of Mixing and Mass Transfer in LBE Process of Steel-making

    pp. 955-960

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    DOI:10.2355/isijinternational.30.955

    Experiments have been conducted to determine the mixing time and mass transfer rates between slag and metal in an LBE model. Complete mixing time of water has been determined by 2 methods-conductimetric and chemical decolourisation. The mixing time in LBE process under all experimental conditions was found to be higher than that in top-blowing model. It has been shown that the amount of bottom gas does not have much effect on mixing time. On the other hand, mixing time decreases as the number of porous plugs increases. Volumetric mass transfer coefficient (KBa) for LBE was found to be higher than that for top-blowing and bottom-blowing processes. The KBa value was found to decrease with increasing gas flow rate and tends to plateau after a certain value of gas flow rate is reached. Mixing and mass transfer results have been explained on the basis of overall turbulence intensity. The model results have been compared with industrial data.
  • Numerical Computations of Fluid Flow and Heat Transfer in Gas Injected Iron Baths

    pp. 961-970

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    DOI:10.2355/isijinternational.30.961

    The time evolution of the flow and temperature fields in industrial scale gas-injected molten iron baths are numerically analyzed. For the vertical injection case, a cylindrical vessel, containing molten iron, is considered. For the horizontal injection system, a cubical vessel is chosen. The Eulerian approach is used for the formulation of both the gas and the liquid phase transports. Turbulence in the liquid phase is predicted using a two-equation k-ε Model. A constant effective viscosity is used for the gas phase turbulence. For the interphase friction and heat transfer coefficients, correlations from the literature are used. In order to realistically model the volume expansion due to gas injection, the computational domain is extended beyond the initial undisturbed liquid height.
  • Sulfide Capacity of Slags and the Lattice Energy of the Component Oxides

    pp. 971-977

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    DOI:10.2355/isijinternational.30.971

    Interaction energy between component anion and cation of an oxide is evaluated from the lattice energy of the oxide. In the calculation of the lattice energy from thermal data and ionization energy of elements, the Born-Haber cycle is used. By assuming that no complex ions are formed in the slag and additivity of pairwise interaction, the interaction energy to oxide anion in a slag is expressed as the average of the lattice energy of the component oxides on the mole fraction base. The averaged lattice energy for sulfide anion in the slag is also derived by the same manner. The oxide anion in calcium oxide is chosen as the reference state in order to correlate the interaction energy with the activity coefficient of the oxide anion. The logarithmic value of the activity coefficient of oxide anion in a slag is expected to have linear relation with the averaged lattice energy obtained from the lattice energy of the component oxides. The relation is examined by the use of sulfide capacity data for several slags, where the activity coefficient of sulfide anion is also taken into account.
  • Effects of Carbon Content on the Diffusion Bonding of Iron and Steel to Titanium

    pp. 978-984

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    DOI:10.2355/isijinternational.30.978

    A commercially pure titanium has been diffusion-bonded to iron and steels of various carbon contents: low carbon steel with 0.01% C (ULC), mild steel with 0.19% C (S20C) and spheroidal graphite cast iron with 3.75% C (FCD). The tensile strength of joints bonded below 900°C was hardly influenced by the carbon content, and increased with the rise in bonding temperature. Above 900°C however, the strength of the ULC/Ti joint was almost independent of the bonding temperature, that of the S20C/Ti joint decreased with the rise in bonding temperature, and that of the FCD/Ti increased. The interlayer forming along the bond interface consisted only of TiC in the FCD/Ti joint and of TiFe and TiFe2 in the ULC/Ti. Since Ti and Fe diffused over much longer distances in the ULC/Ti than in the FCD/Ti, the TiC layer may be considered to interfere with the interdiffusion of Ti and Fe, and consequently to suppress the formation of TiFe and TiFe2 which decrease the joint strength more seriously than TiC. The interlayer in the S20C/Ti consisted of TiC as well as TiFe and TiFe2. The coexisting carbide and intermetallic compounds in the interlayer seems to have more detrimental effect on the joint strength than those formed individually.
  • Gibbs Energies of Formation of TiS and Ti4C2S2 in Austenite

    pp. 985-990

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    DOI:10.2355/isijinternational.30.985

    The Gibbs energies of formation of TiS and Ti4C2S2 from Ti, S and C solutes in austenite are evaluated on the basis of the solubility data measured by Swisher in the Fe-C-S-Ti system. These quantities are employed in equilibrium calculations applied to a series of Ti bearing steels. The results indicate that Ti4C2S2 is expected to predominate in Ti microalloyed steels, whereas both TiS and Ti4C2S2 are likely to be present in Ti modified extra-low-carbon IF steels. These predictions are in good agreement with the experimental observations reported by other researchers.
  • Determination of C, P and S in Steels by Time-resolved Atomic Emission Spectrometry

    pp. 991-996

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    DOI:10.2355/isijinternational.30.991

    The time-resolved method has been applied successfully to the determination of a trace amount of elements C, P and S in steels.
    The following results were obtained by the use of the intensities measured after the time of 50 μs elapsed relative to spark discharge initiation:
    (1) A higher precision analysis was performed. The repeatabilities with standard deviations at a elemental concentration of 10 ppm were 3.7 ppm for C, 0.8 ppm for P and 0.5 ppm for S.
    (2) Spectral interferences were almost avoided. The concentration correction factors were 0.16×10-4 for an interference of Ni on the PI 178.29 nm line and 0.2×10-4–5.8×10-4 for that of Mn on the SI 180.73 nm line.
  • The Relationship between the Degree of Reduction (α) and the Fraction of Reaction (f) during Reduction of Ore-Coal Mixture

    pp. 997-999

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    DOI:10.2355/isijinternational.30.997

  • Influence of a Variety of Grain Boundary Structures on Grain Boundary Segregation

    pp. 1000-1002

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    DOI:10.2355/isijinternational.30.1000

  • Role of Strain-hardening of Steel in Structural Performance

    pp. 1003-1009

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    DOI:10.2355/isijinternational.30.1003

    In the ultimate limit state design and seismic design of steel structures, it is postulated that the structural members have sufficient deformability or rotation capacity. In this context, the relationship of the plastic deformation capacity of steel structural members and the stress-strain curves of their materials are made clear. Namely, to secure the sufficient deformation capacity of structural members, the yield-ratio (the ratio of yield stress to tensile strength) of material should be reasonably low. For flexural members such as beams and beam-columns, the rotation capacity can be evaluated by the complementary energy of materials more exactly. Scattering of yield stress could give an adverse effect on the strength and deformability of steel structures subject to horizontal loading. In this viewpoint, the upper limits of the yield stress and of the yield ratio should be specified in the material standard.

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