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

Tetsu-to-Hagané Vol. 83 (1997), No. 4

  • Improvement of the Melting Reaction in Sintering Process by the Fine Part Selective Granulation of Clayish Iron Ores

    pp. 233-238

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    In order to clarify the melting reaction of iron ores with limestone fines, the melt formation process was directly observed. Single particle firing tests and small packed bed firing tests were carried out for evaluating the sintering performance of sinter mix pseudo-particles.
    It was made clear from the direct observation of melt formation that the melting behavior of solid phases formed from primary melt is important to improve the coalescence of sinter mix pseudo-particles. The iron ores containing quartzite (“quartz-rich iron ore”) are easier in forming the melt than the ores containing much clay minerals (“clayish iron ore”).
    The pseudo-particle using fine clayish iron ores as the adhering part was strong both before and after firing. The results of a small packed bed sintering test showed that segregation of limestone in sinter mix is effective in forming the melt. The increase in limestone concentration of quartz-rich iron are fines which are adhering to a coarse nucleus particle is the most effective for coalescing pseudo-particles and for making a desirable pore network during sintering.
    On the basis of these results, the “fine part selective granulation method of clayish iron ores” was newly proposed to improve the sintering performance of iron ores.
  • The Effect of Reactivity and Strength of Coke on Coke Degradation in the Raceway at High Rate of Pulverized Coal Injection

    pp. 239-244

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    In order to clear the effect of coke quality on coke degradation in a blast furnace raceway at high rate of pulverized coal injection, experiments by a hot model simulating the raceway were carried out. The results were as follows.
    (1) Reactivity and strength of coke effect on combustion behavior of pulverized coal and coke in the raceway, coke degradation in the raceway and the raceway structure.
    (2) Using high reactivity coke, thickness of reacted layer near the lump coke surface is thin.
    (3) Using high reactivity and high strength coke, coke degradation in the raceway is suppressed.
  • A Sound Velocity Measurement System for Thin Steel Sheet Based on Ultrasonic Interferometry

    pp. 245-250

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    A measurement system has been developed in which the sound velocity of thin steel sheet is measured quickly and displayed as a two-dimensional distribution. In the system the velocity is obtained from the peak amplitude of ultrasonic wave (multiple interfered echo reflected from the specimen). This system is characterized by the use of ultrasonic tone burst wave being transmitted through specimen to eliminate the disturbance of the first surface echo. This measurement system was applied to the observation of the growth of secondary recrystallized grain in grainoriented electrical steel sheet. The results were as follows.
    1) The amplitude of multiple echo increases with the number of burst waves up to about 50 waves.
    2) The relation between the amplitude of multiple echo and the sound velocity shows a typical resonance curve in which half-width is about 450m/s and the maximum inclination is 0.34% per lm/s.
    3) The two-dimensional display of the secondary recrystallized structure by the ultrasonic wave method shows a good agreement with that by the conventional macro-etching technique.
    4) This ultrasonic wave method is applicable for the observation of the growth of secondary recrystallized grain in grainoriented electrical steel sheet.
  • The Effect of Deformation Conditions on the Occurrence of Fluting at 3-pieces Can Body Making

    pp. 251-256

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    The continuously annealed tinplate with low carbon chemistry often exhibits the “fluting” trouble which is associated with stretcher strain defect, when it is roll-formed for making a 3-pieces can body. For preventing the occurrence of fluting, the influence of the forming conditions is focused in this study, leading to following results. The “flexor treatment” just prior to roll forming, recognized as effective for solving the problem, is attributable to the reduction of both the yield point elongation and yield strength in the tinplate. Furthermore, the tendency of the fluting occurrence can be drastically decreased by employing high speed or low temperature roll-forming condition. A greater number of stretcher strain pattern on the deformed sheet is introduced by the high speed or low temperature deformation. This, in turn suppresses clear recognition of the stretcher strain pattern preferably.
  • Heat Transfer Characteristics with Single and Multi-stage Flat Spray Nozzles on a Hot Vertical Surface Cooling

    pp. 257-262

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    In order to improve water cooling technique for flanges in rolled H-shapes for the prevention of cooling buckling on thin web, an experimental study on a hot vertical surface cooling with single and multi-stage spray nozzles was carried out.
    First, the effects of nozzle pressure, nozzle angle and nozzle-plate distance on heat transfer coefficient of a hot vertical surface were investigated with a single spray nozzle. Next, with multi-stage spray nozzles the effect of flowing water from the upper area on heat transfer coefficients of the lower water strike zone and flowing water zone was investigated.
    The results obtained are summarized as follows.
    (1) The heat transfer coefficient of water strike zone with a single spray nozzle was described by water flux which is functions of nozzle pressure, nozzle angle and nozzle-plate distance.
    (2) In the case of high temperature with a single spray nozzle, the heat transfer coefficient ratio between flowing water zone and water strike zone is not affected by the cooling conditions, such as nozzle pressure, nozzle angle and nozzleplate distance.
    (3) However, in the case of low temperature, the ratio between flowing water zone and water strike zone on heat transfer coefficient strongly depends on the nozzle operating conditions.
    (4) On the other hand, in the case of multi-stage spray cooling, the existance of flowing water from the upper area enhances heat transfer coefficient of lower flowing zone. The maximum ratio of heat transfer coefficient between flowing water zone with water flowing down from above and without is from about 1.3 to 1.7.
  • A New Preparation Technique of Surface to Microstructural Examination of Heat Resisting Steels and Alloys by Using Penning Discharge Micro-Sputtering

    pp. 263-268

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    The microstructure of heat resisting steels and alloys for high-temperature plants changes depending on operating conditions and time. The microstructural changes affect the mechanical properties of the materials at high temperatures. Microstructural examination of the materials is generally carried out using etching techniques by chemical method. For chemical etching, however, high skill is required to produce clear microstructure.
    In this research, penning discharge micro-sputtering techniques were applied for etching a variety of heat resisting steels and a super alloy. The etching of 1Cr-1Mo-0.25V ferritic and 316H austenitic steels and Ni-base Inconel 713C superalloy was carried out in the vacuum chamber of a micro-sputtering apparatus..All of the materials exhibited clear microstructure using micro-sputtering, irrespective of different chemical compositions and different history of the materials. The grain boundaries, creep voids and precipitates such as carbides and σ phase were characterized. It was concluded that the present method required lesss skill and the resultant microstructure was insensitive to sputtering conditions.
  • Electrical Resistivity Changes during Isothermal Aging at Various Temperatures in Ti-10V-2Fe-3Al Alloy

    pp. 269-274

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    The changes in electrical resistivity and Vickers hardness during isothermal aging in near β titanium alloy Ti-10V-2Fe-3Al which is used as the aircraft structure materials are investigated. The results reveal that the electrical resistivity of this alloy decreases during isothermal aging at 603K813K, while the Vickers hardness increases during the aging. However, the both changes in electrical resistivity and Vickers hardness correspond to each other. Also, the results obtained by X-ray measurements show that the precipitation of α phase proceeds during isothermal aging. This implies that the change in the resistivity reflects the behaviour of α phase precipitation during aging. Further, from the data of the X-ray and resistivity measurements it is found that the activation energy for the precipitation has two different values depending on aging temperatures above 723K or below 663K.
  • Effects of HIP Treatment and Heat Treatment on Tensile Properties at Room Temperature of Cast TiAl-Fe-V-B Alloy

    pp. 275-280

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    A gamma alloy, Ti-46.7Al-1.3Fe-1.1V-0.35B(mol%), has been developed as a casting materials for turbine components, replacing superalloys. This alloy is characterized by the addition of Fe and V which improve castability. In order to use this alloy widely, improvements of mechanical properties are required. Thus, microstructural evaluation of various HIP treatments was studied to decrease amounts of casting defects. HIP treatment made a large contribution to improve tensile properties and to reduce a scatter of mechanical value. As compared with other TiAl alloys, the grain growth of an alpha phase during heat treatment at higher temperatures than alpha transus temperature in the TiAl-Fe-V-B alloy was slower. Moreover, the optimum conditions of HIP treatment and heat treatment were determined to further improve the room temperature strength and ductility in this study. As a result, we developed heat treatment process to produce a duplex structure which improves ductility. The alloy with the duplex structure by the HIP and heat treatments had 550MPa tensile strength and 1.8% elongation at room temperature. These results show that the HIP and heat treatments improve both of strength and ductility. The stage 5 blades for use of low pressure turbine were cast and its engineering applicability was demonstrated by 500 flight cycles test in a CF6 engine at GEAE, in November, 1994.
  • Microstructure Dependence of Small Fatigue Crack Growth in Beta Ti-15Mo-5Zr-3Al Alloy

    pp. 281-286

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    Growth behaviour of small fatigue cracks has been investigated on three materials with different microstructures of a beta Ti-15Mo-5Zr-3Al alloy which were solution treated at 735°C, 850°C and 1000°C, followed by aged at 500°C (STA735, STA850 and STA1000) at a stress ratio of-1 under axial loading in laboratory air. The da/dN-Kmax relationships for STA735 and STA850 were almost the same as the da/dNK relationships for large cracks, while STA1000 showed initially lower growth rates than large cracks, and then the growth rates rapidly increased and became faster at an intermediate Kmax regime than those of large cracks. After allowing crack closure, STA850 and STA1000 still exhibited enhanced growth rates, which was found to be attributed to the crystallographic nature of small crack growth based on a close examination of the fracture surfaces. The trace of the crack front remained on the fracture surfaces of STA850 and STA1000 represented the transition from the microstructurally small crack to the mechanically small crack, which has occurred at a/d=2.63.9 for STA850 and a/d= 1.62.1 for STA1000, where a and d were the crack depth and the beta grain size, respectively. Of three materials, STA1000 showed the lowest growth resistance of small cracks at intermediate Kmax and ΔKeff regimes. Furthermore, it was found that all the materials of the beta alloy exhibited lower growth rates at low Kmax regime than an annealed Ti-6Al-4V alloy, but the difference disappeared in terms of ΔKeff, indicating that crack closure was responsible for the difference in growth behaviour between both alloys.

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