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

Tetsu-to-Hagané Vol. 85 (1999), No. 4

  • Coking Pressure and Coke Shrinkage in Coke Oven

    pp. 289-294

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    Relationship between coking pressure, lateral shrinkage and vertical shrinkage during carbonization in coke oven was investigated by the use of movable-wall type test coke oven. The lateral shrinkage started to rise after the coking pressure disappeared. The final lateral shrinkage was 25 mm and slightly increased with increasing volatile matter content. The vertical shrinkage increased in proportion to the lateral shrinkage after the disappearance of coking pressure. The final vertical shrinkage decreased with increasing coking pressure and decreasing vertically applied force. The time when the vertical shrinkage starts to rise is considered to depend on the balance between the friction force between coke and oven wall caused by coking pressure and the vertical force applied on coke. The coke layer is pressed against the oven wall by high coking pressure and the coke cake is prevented from lowering which would result in wider fissures between coke lumps and thus harder pushing.
  • Deformation Behavior of Borated 18Cr-8Ni Stainless Steel Accompanied by Eutectic Structure during Solidification

    pp. 295-300

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    Tensile strength and ductility behavior of borated 18Cr-8Ni stainless steel samples during solidification has been studied by the technique for high temperature tensile test. Density of samples has been measured by a sessile drop method during solidification.
    Borated 18Cr-8Ni stainless steel has formed eutectic morphologies in addition to dendritic structure during solidification. The ratio of eutectic structure increased with increasing boron concentration. Eutectic composition was 2.2 mass% boron from the result of differential thermal analysis. The behavior of tensile strength and ductility has depended on the morphologies of solidification microstructure. When the ratio of eutectic structure was more than 70%, tensile strength and ductility has not appeared until fraction of solid became unity. Density of samples was unaffected by eutectic structure.
  • Behavior of Hydrogen Induced Cracking Originated in Centerline Segregation

    pp. 301-306

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    Influence of centerline segregations on hydrogen induced cracking for sour gas line pipe was investigated. As Crack Length Ratio (CLR) mainly depends on centerline segregation in the ease of well-controlled clean steel, it may discuss CLR with centerline segregations. Distribution of centerline segregation grains and P, Mn segregation ratio are represented by the experimental formulae for each casting condition. As a result, effects of casting conditions, soaking conditions and pre-reduction conditions on CLR can be estimated qualitatively, using HIC sensitivity paramenter with those formulae. Estimated CLR corresponds fairly well to measured CLR for several heats.
  • Effect of Refractory Materials on Inclusion Deposition of Immersion Nozzle in Continuous Casting and Mathematical Modeling of Inclusion Deposition

    pp. 307-313

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    New immersion nozzle materials preventing inclusion deposition have been investigated by laboratory scale test. A new mathematical model has been proposed to explain the behavior of inclusion in the turbulent boundary layer near the nozzle and deposition rate of inclusions in the molten steel has been numerically evaluated.
    (1) The quantity of deposited inclusions has drastically decreased in the materials composed with high Al2O3 in comparison with Al2O3-C one. There is no deposition of inclusions on the material composed with pure Al2O3, (Sapphire).
    (2) About 30% of the inclusions less than 20μm in diameter reach at laminar sublayer and they are forced to move onto the refractory wall due to the interfacial tension gradient between inclusions and molten steel, formed by concentration gradient of silicon etc. in molten steel.
    (3) Deposition rate of inclusions in the molten steel was evaluated to be 0.75μm/s (1.35 mm thickness in 30 min) which is almost equal to the experimental results.
  • Morphology of Electrodeposited Zinc-Cobalt Binary Alloys

    pp. 314-318

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    Zinc-cobalt electrodeposited steel sheet is adopted for automobile bodies for its high corrosion resistance with small cobalt content. This deposit exhibits fine grains and its refinement mechanism has been discussed. The deposits of various zinc contents have been prepared galvanostatically from sulfate baths and examined by SEM and FESEM. The single η-phase of 99.7 at% zinc exhibits morphology of hexagonal columnar crystal having triangular pyramidal shape with the η-phase plates stacking in the direction of c-axis. At 99.2 at% zinc, finer hexagonal crystals with the same orientation form on the {10·0}η of this hexagonal columnar crystals. With the decrease of zinc content to 98.2 at% zinc these finer hexagonal crystals form in between the larger hexagonal columnar crystals with random orientation. The γ1-phase forms in addition to the η-phase. With further decrease of zinc content to 93.4 at% zinc, larger hexagonal columnar crystals disappears, and the entire deposits become finer hexagonal crystals. The γ-phase forms in addition to the η/γ1-phase.
  • Effect of Resin Coating on Electropainting Behaviour of Organic Coated Steel Sheets

    pp. 319-324

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    Thin organic coated steel sheets have been electropainted for home electrical appliances. Therefore, it is important to make clear the exact mechanism of electropainting on organic coating. In this study, the effect of resin coating on electropainting behaviour of thin organic coated steel sheets was investigated by using an acrylic cationic electropaint for one-coat finish. Measurement an initial current of electropainting, observation of uncured as-deposited paint film by video microscope system and counting of conductive points of organic coated steel sheets were conducted. When resin coating weight of organic coated steel sheets is large, bubbles are left in the paint film, the paint film thickness increase largely and surface of the paint film becomes rough. The reason is that microscopic conductive points of the organic coated steel sheets decrease and electrodeposited paint film becomes random in thickness at the initial stage of electropainting. So the electropainting current concentrates locally on the spots where the paint film is thin, then thick and porous paint film which contains bubbles is formed. It is clear that the electropaintability of organic coated steel sheets depends on the morphology of initially deposited paint film. Therefore, it is possible to improve electropaintability by controlling the microscopic conductive points of resin coating.
  • Effect of the Cyclic Hydrogen Charging and Discharging on the Mechanical Properties of SUS304 Steel

    pp. 325-331

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    Hydrogen effect on the mechanical properties in austenitic stainless steels has been studying, using the hydrogen charging method with high temperature and high pressurized hydrogen atmosphere or electrochemical cathodic charging. In these methods, the mechanical testing must be done as soon as possible after charging or the test pieces must be kept soon in the box with dry ice or liquid nitrogen after the hydrogen charging until mechanical testing. So these methods are difficult to apply to the case which the mechanical testing can not be done soon after the hydrogen charging i.e. the case of handling the irradiated materials in the hot cell by the manipulator. Accordingly the repeating method of hydrogen charging and discharging was proposed. Namely soon after the hydrogen charging by electrochemical cathodic charging, the hydrogen discharging by heating is conducted and this process is repeated. After this method conducted, the mechanical properties and the susceptibility of the intergranular cracking was investigated.
    The sensitized austenitic stainless steel showed the lower elongation and more average depth of intergranular cracking by the repeat of hydrogen charging and discharging than by the hydrogen charging only. Furthermore the mechanism of the intergranular cracking was investigated with measuring the hydrogen concentration and the martensite phase value in the test pieces. This mechanism seemed to be occurred by the hydrogen induced martensite phase made on the grain boundary with this repeating method of hydrogen charging and discharging.
  • The Roles of Globular M23C6 Carbides in Hydrogen Attack Resistance in C-0.5Mo Steels

    pp. 332-339

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    Metallographic observations on the C-0.5Mo steel components in petroleum refineries and experimental studies revealed that unusual ferritepearlite structures with quasi-M23C6 carbides were more susceptible to hydrogen attack than standard ferrite-bainite structures with M3C carbides. Post weld heat treatments (PWHT) were found to promote methane bubble formation. In order to explain these microstructural effects on hydrogen attack susceptibility, thermal stability of carbides and the strength of interface between carbides and the matrix were examined.
    C-0.5Mo steel specimens with varied microstructures were exposed to high pressure hydrogen, and the temperature dependence of the emitted methane concentration was measured with a gas chromatograph. The temperature at which methane evolution took place and the changes in methane concentration with temperature were both unaffected by the microstructures. In low strain rate tensile tests, void formation around carbide particles started at lower strain in a ferrite-pearlite microstructure with quasi-M23C6 carbides than in a ferrite-bainite microstructure with M3C carbides. Voids increased in number more rapidly with strain in the former than the latter. After PWHT, voids started to form at lower strain compared with before PWHT probably due to coarsening of carbides.
    Therefore, it can be concluded that hydrogen attack in C-0.5Mo steels is not governed by stability of carbides but by the difference in total area of methane formation site between the two.
  • Effect of Heat Treatment on Bonding Characteristics and Interfacial Microstructures in Explosively Welded Ti/SUS430 Stainless Steel Clad

    pp. 340-345

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    Effect of heat treatment on bonding characteristics and interfacial microstructures in explosively welded titanium/SUS430 ferritic stainless steel clad was investigated. The average shear strength of the clad annealed at 1073K for 3.6ks was 338 MPa and was equivalent to about 60% of that of an as-welded clad. The strength of the clad annealed at 1073K gradually decreased to 242 MPa with increasing holding time up to 360 ks. The same tendency was obtained from the clad annealed at 1173K. On the other hand, the strength of the clad annealed at 1273K drastically decreased to 107 MPa with increasing holding time up to 360 ks. The clad annealed at 1073 and 1173K yielded TiC layer at the bonding interface, while the reaction layer in the clad annealed 1273K consisted of TiC, FeTi, Fe2Ti and χ (Fe29Cr13Ti8) from titanium side. It was noted that chromium existed in the Fe2Ti, which has wide solubility limit for chromium, and χ compounds formed at the SUS430 side. The TiC layer in the former clads acts as a barrier for diffusion of titanium, iron and chromium across the bonding interface and prevents the growth of intermetallic compounds. The clad formed TiC layer at the bonding interface preserved high bonding strength even after prolonged annealing.
  • Effect of Boron on Planar Anisotropy of r-value in Extra-low-C IF Steel Sheet

    pp. 346-351

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    The planar anisotropy of r-value was investigated of extra-low-C, Ti and Nb added interstitial-atom free (IF) steels with various B contents. The anisotropy of r-value is preferably decreased by addtion of B, although mean r-value itself after cold rolling and recrystallization treatment is slightly lowered. Addition of B does not affect the grain size of hot band, leading to small influence on r-value in cold-rolled and annealed sheet. In the texture of the hot band, strong γ- and α-fibres, especially, {001}<110>, {332}<113>, {113}<110> are formed by B addition. On the other hand, no specific sharp orientation is obtained in B-free steel. By cold rolling and recrystallization, these hot rolling orientations are rotated toward stable orientations. It is estimated that these hot rolling orientation in ultra-low-C IF B-bearing steel decrease the planar anisotropy of r-value after the cold rolling and recrystallization treatments.

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