Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Volume 80 , Issue 10
Showing 1-16 articles out of 16 articles from the selected issue
  • Isao SAKAMOTO, Nobuyuki HAYASHI
    1994 Volume 80 Issue 10 Pages 735-741
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
  • Manabu IGUCHI, Tomoyuki CHIHARA, Tomoaki KURANAGA, Hiroshi UEDA, Shige ...
    1994 Volume 80 Issue 10 Pages 742-747
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    As a fundamental study on the RH and DH degassing processes, air was injected into a cylindrical water bath under a reduced surface pressure through a centered single-hole bottom nozzle. The shape of bubbles during expansion near the nozzle and the subsequent dispersion of the bubbles in the course of rising in the bath were observed using a high-speed video camera. The bubble characteristics such as gas holdup, bubble frequency, mean bubble rising velocity, mean bubble diameter were measured with a two-needle electro-resistivity probe.
    The frequency of bubbles generated at the nozzle exit under reduced pressure almost agreed with that formed under the atmospheric pressure and the same mass flow rate. Accordingly the effect of reduced pressure on the frequency of bubble formation is negligible. Bubbles generated under reduced pressures expanded near the nozzle up to the volume associated with the hydrostatic pressure. The bubble characteristics in the region away from the nozzle weres atisfactorily approximated by those observed for gas injection under the atmospheric surface pressure and the same volumetric gas flow rate.
    The total interfacial area between bubbles and liquid under reduced pressures was also determined as one of influential parameters for the metallurgical reactions occurring in a bath with gas injection. It was dependent on thesquare root of the gas flow rate after expansion, and an empirical equation of it was proposed.
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  • Nobuya SHINOZAKI, Nobuo ECHIDA, Kusuhiro MUKAI, Yoshiroh TAKAHASHI, Ya ...
    1994 Volume 80 Issue 10 Pages 748-753
    Published: 1994
    Released: January 18, 2010
    JOURNALS FREE ACCESS
    An attempt to clarify the clogging mechanism of immersion nozzle from the standpoint of wettability has carried out by preparing the following substrates: substrates of Al2O3 and ZrO2-CaO, which are main components of nozzlematerials, substrates of Al2O3 and Al2O3-MgO, main components of inclusions, and substrate of Al2O3-CaO, reaction product by contact of inclusion with ZrO2-CaO nozzle. Contact angles between these substrates containing CaO orMgO lower than 20mass% and liquid irons were measured at 1873K.
    In the cases using irons containing the same level of oxygen as molten steel for continuous casting, the following relations are obtained by comparing the values of contact angle obtained for each substrate;
    Contact angle: Al2O3, Al2O3-MgO>ZrO2-CaO≥Al2O3-CaO.
    These results indicate qualitatively that the use of ZrO2-CaO refractory instead of Al2$#O213 refractory as immersion nozzle may lead to a retardation of adhesion of Al2O3 inclusions to the refractory, though decrease in force of adhesion dueto the observed changes in wettability is only about 30%.
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  • Shinichiro YOKOYA, Yutaka ASAKO, Shigeta HARA, Julian SZEKELY
    1994 Volume 80 Issue 10 Pages 754-758
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    In conventional continuous casting system, using a submerged nozzle with side-pouring holes, it is very difficult to achieve a low and uniform velocity distribution of molten metal stream in front of the holes.
    In order to solve such a problem, fluid flow characteristics imparting a swirling motion at the entrance region of a nozzle have been investigated, using a water model. It has been shown that a uniform velocity distribution at the outlet can be obtained imparting a swirling motion in the entrance region of the divergent nozzle. This strongly suggests that the outlet flow pattern in the practical continuous caster can be controlled by introducing a swirling flow in the molten metal using an externally imposed rotating magnetic field.
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  • Shinichiro YOKOYA, Richardo WESTHOFF, Yutaka ASAKO, Shigeta HARA, Juli ...
    1994 Volume 80 Issue 10 Pages 759-764
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    A new method obtaining a low and uniform velocity distribution at the immersion nozzle outlet was developed imposing a swirling flow pattern at the entrance region of a divergent nozzle in the preceding paper. Results of the water model are in good accordance with those calculated using a turbulent k-ε model. In addition, the mechanism for obtaining the uniform flow pattern at the nozzle outlet was correlated with the flow pattern of the nozzle and the swirl strength. Those results show that by changing the strength of the swirl motion in the pouring tube of an immersion nozzle, it is easy to control the flow pattern and the direction of the flow at the nozzle exit. A same numerical investigation was also done for a molten steel system in which swirl is generated by a rotating magnetic field imposed on the pouring tube. Such an effect of the swirling can provide a uniform and low velocity flow of molten steel at the nozzle outlet, which is very desirable for continuous casting purpose.
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  • Ryoji TSUJINO, Arata TANAKA, Akira IMAMURA, Daijyo TAKAHASHI, Shozo MI ...
    1994 Volume 80 Issue 10 Pages 765-770
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    Conditions of deposition of alumina and metal on ZrO2-CaO-C refractory has been investigated in comparison of Al2O3-C refractory by laboratory scale test. The results are summarized as follows.
    (1) When high aluminum and alumina inclusions were contained in the molten steel, ZrO2-CaO-C refractory was easier to be deposited than Al2O3-C one.
    (2) The deposition may be composed of two steps.
    The first is the formation of fine oxide layer (the network alumina) in the hot face during very short time after immersion.
    The second is the deposition of non-metallic inclusions on the fine oxide layer.
    (3) The generation of the fine oxide layer is due to the following reactions. Direct reaction of aluminum in the molten steel with silica and zirconia contained in the refractory. Suboxide gases (SiO, ZrO) reduced by graphite in the refractory react with aluminum in the molten steel.
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  • Kazuki FUJIWARA, Shuji OKAGUCHI
    1994 Volume 80 Issue 10 Pages 771-776
    Published: 1994
    Released: January 18, 2010
    JOURNALS FREE ACCESS
    Effects of deformation in unrecrystallized austenite region on isothermally transformed bainite structure were investigated in low carbon Nb-B bearing steels.
    SEM observation shows, in a case of non-deformation, a number of lath-like bainitic ferrite plates form in parallel from austenite grain boundaries, showing a typical upper bainite structure. A 30%-deformation has little influence on the length of bainitic ferrite plates, although it shapes them like a sheaf of bows. In contrast, a 50%-deformation significantly decreases their length. However, it is confirmed that those bainitic ferrite plates are also surrounded by two sets of habit planes close to {451}a, which suggests the bainitic ferrite transformed from heavily deformed austenite has the same crystallographic characteristic as the typical upper bainite has. Those refinement of bainitic ferrite plates leads to complicate an appearance of the microstructure.
    A quantitative analysis reveals the length of bainitic ferrite plates, after 75%-deformation, is consistent with the subgrain size estimated from previous study in low carbon steels. Therefore, subgrain boundaries introduced by heavy deformation are considered to play an important role in refinement of bainite structure, namely they will stifle the growth of bainitic ferrite plates and also supply further nucleation sites of them.
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  • Yuji OKAMI, Masahiro ABE, Tsunehiro YAMAJI, Yoshikazu TAKADA, Hironori ...
    1994 Volume 80 Issue 10 Pages 777-782
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    It is wellknown that 6.5% Si steel has excellent soft magnetic properties, but high Si steel more than 4% Si are so brittle that it is impossible to manufacture thin gauge steel sheets using the conventional rolling process.
    Using the siliconizing method, we have succeeded in developing the world's first non-oriented 6.5% Si steel sheets for commercial production in coil form, with a thickness range 0.1-0.5 mm.
    The 6.5% Si steel sheets have no void and exhibit excellent soft magnetic properties, a high frequency core loss W10/400 of 9.9 W/kg for a thickness of 0.3mm. In addition, the product has good workability.
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  • Takanori NAKAZAWA, Nobuhiro FUJITA, Hidetaka KIMURA, Hajime KOMATSU, K ...
    1994 Volume 80 Issue 10 Pages 783-788
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    The 316MN steels with improved creep rupture properties were developed for structural materials of fast breeder reactors. To develop weld materials for the 316MN steels the effects of C, N, Mo, and delta ferrite on creep rupture properties of weld metals were investigated. Creep rupture strength and rupture ductility were improved by reducing carbon and increasing nitrogen content. Delta ferrite, which is necessary for preventing hot weld cracking, reduces the rupture strength but increases rupture ductility. On the basis of these test results, low carbon and medium nitrogen type 316 and 16-8-2 weld materials were developed. Creep rupture strength of bot hweld metals is equivalent to that of base metal. Rupture ductility is also comparatively high and independent of rupture time. Some intermetallic compounds such as Laves and sigma phases, etc., which precipitate in delta ferrite during creep or high temperature aging, do not affect creep rupture properties, but the sigma phase seriously reduces the Charpy impact toughness. The loss of toughness of type 16-8-2 weld metal is less than that of type 316 weld metals.
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  • Yomei YOSHIOKA, Daizo SAITO, Kazunari FUJIYAMA, Nagatoshi OKABE
    1994 Volume 80 Issue 10 Pages 789-794
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    Transition pieces of Hastelloy X in gas turbine combustion are suffered from significant creep deflection with material degradation during the operations. The main purpose of this study is to clarify the effect of microstructural changes on minimum creep rate and rupture life, and is also to develop the creep life prediction method from microstructural observation and the component's operating history.
    Specimens of Hastelloy X were aged for up to 104h in the temperature range of750°-900°C. By using these prior-aged specimens, metallurgical observations and short term mechanical tests were carried out to evaluate the precipitation behaviors and the degree of degradation. The accomplishments of this study were as follows;
    (1)The amount of intergranular and intragranular precipitates increases during the aging under the temperature of 750°-900°C. The former one contributes to strengthening the creep resistance and the latter one contributes to weakening it.
    (2) Minimum creep rate(εm) was explained as functions of volume fraction of precipitates at the as-solutioned (Vo) and aged (V) conditions, area fraction of intergranular precipitates (ρ), applied stress(σ), aging temperature(Ta), test temperature (T), and activation energy of aging(Qa) and creep (Qc). The equation was as followed.
    εm=[B*o+A*1(1-ρ)(V-Vo)2exp(-Qa/kTa)]σnexp(-Qc/kT)
    (3) Creep rupture life was also explained from the minimum creep rate by using the Monkman-Grant equation for the aged material of Hastelloy X.
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  • Jianzhong SHI, Takao ENDO
    1994 Volume 80 Issue 10 Pages 795-800
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    Creep testing was conducted on the pre-crept specimens of a 2.25Cr-1Mo steel under constant load. The amount of pre-strain was between 4.4 and 12.0%, and the range of temperature and initial stress was 853 to 903 K and 78.4 to 127.4 MPa, respectively. The relation between creep rate, ε and creep strain, ε was expressed as below over a wide range of creep strain :
    ε=εOexp(sε),
    where s is the acceleration factor, ε0 is the imaginary initial strain rate, and the stress and temperature dependence ofεO is given as:
    ε0=Aσnexp(-QO/RT),
    where QO is the apparent activation energy for creep of the magnitude of 400±10kJ·mol-1, σ is the true stress, n is the stress exponent of the magnitude of 9.7 and A is the mechanically defined structure factor expressed as below:
    A=AOexp[(m-n)εp],
    where AO is the structure factor for virgin specimens and m is the constant. These experimental facts lead to the conclusion that pre-strain and creep strain do not alter the creep mechanism but cause the increase in the mechanically defined structure factor, and creep life, tr is given by tr=1/ (sεO).
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  • Kiyoshi KUSABIRAKI, Yoshiyuki YAMAMOTO, Takayuki OOKA
    1994 Volume 80 Issue 10 Pages 801-806
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
    Microstructures, mechanical properties, and crystal structures of Ti-(50-52)mol%Al alloys containing Sn up to 5mol% as a third element have been studied by using an optical microscope, a transmission electron microscope, a micro-Vickers hardness tester, and an X-ray diffractometer. Results obtained are as follows: The amount of Ti3Al (α2) phase existing in as-cast alloys was decreased by addition of Sn and it disappeared by anannealing for 604.8ks at 1273K. But the Ti3Sn phase formed in the cast alloys containings Sn did not disappear by the annealing. The Ti6Sn5 phase was formed in the Ti-50mol%Al-5mol%Sn alloy by the annealing. Both of the lattice parameter c and the axial ratio c/a of the LlO-type Al-rich intermetallic compound TiAl (γ phase) increased with increasing Sn content. Tin atoms in the γ phase occupy predominantly in the Ti site. The amount of mutual exchanges of Ti and Al atoms in lattice sites increased with increasing Sn content in the γ phase.
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  • 1994 Volume 80 Issue 10 Pages N552b
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
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  • 1994 Volume 80 Issue 10 Pages N552
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
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  • 1994 Volume 80 Issue 10 Pages N552a
    Published: 1994
    Released: June 19, 2009
    JOURNALS FREE ACCESS
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  • Setsuo TAKAKI
    1994 Volume 80 Issue 10 Pages N529-N535
    Published: 1994
    Released: January 18, 2010
    JOURNALS FREE ACCESS
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