Tetsu-to-Hagane
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Volume 78, Issue 4
Displaying 1-24 of 24 articles from this issue
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  • Challenge of Direct Methods to Indirect Ones in the History of Iron and Steelmaking
    Change and Development of Smelting Reduction
    Yasuto SHIMOMURA
    1992 Volume 78 Issue 4 Pages 509-519
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_509
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  • Scrap Melting Process-Current Status and Future Prospect
    Kazushige UMEZAWA
    1992 Volume 78 Issue 4 Pages 520-526
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_520
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  • Mechanisms of Collision and Coagulation between Fine Particles in Fluid
    Shoji TANIGUCHI, Atsushi KIKUCHI
    1992 Volume 78 Issue 4 Pages 527-535
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_527
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    [in Japanese]
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  • Thermal Decomposition Rate of Fine Iron Ore
    Xing-guo XIAO, Masakata SHIMIZU, Shin-ichi INABA
    1992 Volume 78 Issue 4 Pages 536-543
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_536
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    In order to clarify the thermal decomposition behavior of fine iron ore which is injected into the raceway of a blast furnace, thermal analyses of fine iron ore have been made under various atmospheric conditions (N2, CO2, air, O2 and N2+O2 with different oxygen concentrations from 1% to 25%), particle size (average dia.: 55, 155 and 325 μm) and heating rate (0.033, 0.167 and 0.33 K/s). A kinetic analysis of the reaction (3Fe2O3=2Fe3O4+1/2O2) has been made based on measured thermalgravimetric curves by the Coats' method. Its results show that the reaction rate could be described by a second order reaction rate equation with relation to unreacted degree.
    dα/dt=k(1-α)2
    k=exp(A-E/RT)
    Furthermore it was found that the starting temperature (TD1) and the kinetic behavior of the reaction were independent of the particle size in the range from 55 to 325 μm. However, they were strongly affected by the oxygen potential of the gas atmosphere. Empirical equations to estimate TD1, E and A were obtained as a function of PO2 in the gas atmosphere as follows:
    TD1=75560/{44.56-ln[PO2/(1.013*105)]}
    E=20730/{6.543-ln[PO2/(1.013*105)]}
    A={14.43+ln[PO2/(1.013*105)]}/102/6.9306
    Using these equations, the thermal decomposition processes of iron ore were analyzed under various conditions and the results coincided well with our experimental results. Under heating conditions simulating raceway in a blast furnace, it was predicted that the injected fine iron ore could be almost decomposed from Fe2O3 to Fe3O4 in the raceway.
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  • Decrease of Carry-over of Fine Ore Added into Smelting Reduction Furnace
    Hiroyuki KATAYAMA, Masatoshi KUWAHARA, Takamasa OHNO, Masao YAMAUCHI, ...
    1992 Volume 78 Issue 4 Pages 544-550
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_544
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    In smelting reduction, it is desirable to use fine ore without agglomeration. In order to find the proper condition for fine ore addition to bath without injection, experiments involving a cold model and smelting reduction were performed.
    (1) In the cold model test, a stream of fine materials (iron ore or coke) was passed into the gas of the counter flow. The rate of carry-over (g/s) depended on the surface area of the stream. The ratio of carry-over (%) decreased to less than 5% when the rate of supply was increased. Therefore, it is possible to decrease the ratio of carry-over during addition by decreasing the specific surface area of the stream, independent of the sort and size of fine materials.
    (2) When fine ore was added through a hole in the shoulder of a 100 t smelting reduction furnace, the ratio of carry-over was negligible when compared with the amount of dust originating from molten metal. So, it has been confirmed that top addition of fine ore without agglomeration is practical.
    On the other hand, in the case of a fine carbonaceous material, the ratio of carry-over was high, even with an appropriate method of adding the fine ore.
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  • Oxygen Equilibrium between Liquid Iron and CaO-saturated FetO-CaO-CaF2-Slags
    Shigeta HARA, Tetsuji TOKONAMI, Kazumi OGINO
    1992 Volume 78 Issue 4 Pages 551-556
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_551
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    Equilibrium between molten iron and molten FetO-CaO-CaF2 slags was established at 1 600°C under a CaO-saturated condition. The results are summarized as follows,
    (1) Oxygen content in liquid iron equilibrated with CaO-saturated iron oxide melt is given by the following equation.
    log[% O]=-5240/T+1.743 (1848<T/K<1933)
    (2) Solubility line of CaO in FetO-CaO-CaF2 melts at 1600°C equilibrated with liquid iron is similar to that saturated with the slag equilibrated with solid iron at 1 450°C reported by HAWKINS and DAVIES.
    (3) Addition of CaF2 to Fet-CaOsat. melts decreased the oxygen contents in liquid iron, while the activity coefficient of FetO in the melts, γFetO incraesed with increase of CaF2 content.
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  • Equilibrium Phosphorus Distribution between CaO-saturated FetO-CaO-P2O5-CaF2 Slags and Liquid Iron
    Shigeta HARA, Tetsuji TOKONAMI, Kazumi OGINO
    1992 Volume 78 Issue 4 Pages 557-563
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_557
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    Equilibrium phosphorus distribution between FetO-CaO-P2O5-CaF2 slags and liquid iron has been studied at 1600°C under a CaO-saturated condition. The results are summarized as follows,
    (1) Increase of P2O5 content in CaO-saturated FetO-CaO-P2O5 slags contributes to an increase of the activity coefficient of iron oxide, γFetO and also a slight increase of the ratio (Fe3+/Fe2+), but decreases the activity coefficient, γP2O5.
    (2) For slags containing approximately 10 mass% P2O5, an addition of CaF2 contributes to a decrease of the γP2O5 as follows, logγP2O5=2.52NFetO-1.32NCaF2-19.4
    The addition of CaF2 also increases the γFetO and the ratio (Fe3+/Fe2+). It suggests that CaF2 in molten slags behaves as a basic component.
    (3) For slags having 10 mass% P2O5, most suitable slags for the dephosphorization are those containing 40-50 mass% CaF2.
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  • Partitions of Nitrogen and Sulfur between CaO-Al2O3 Melts and Liquid Iron
    Ryo INOUE, Hajime INOUE, Hideaki SUITO
    1992 Volume 78 Issue 4 Pages 564-571
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_564
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    Nitrogen and sulfur distribution ratios between CaO-Al2O3 slag and Fe-0.000133 mass% Al alloys were measured in the temperature range of 1823 to 1923 K, using Al2O3 and CaO crucibles. The distribution ratios under a CaO crucible were higher than those under an Al2O3 crucible, and increased with an increase of Al content. Nitride and sulfide capacities defined by CN3-=(mass% N)·PO23/4/PN21/2 and CS2-=(mass% S)·PO21/2/PS21/2, respectively, which were obtained by using the reported values for activity of Al2O3, agreed well those directly measured in a gas-slag experiment under an Al2O3 curcible, but disagreed with those under a CaO crucible. Activities of Al2O3 in the CaO-Al2O3 melts saturated with CaO were evaluated based on the results in the gas-slag experiments.
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  • Mathematical Modelling on Liquid Metal Flow in a Cold Crucible Coupled with Heat Transfer
    Tsutomu TANAKA, Koichi KURITA, Atsuhiko KURODA
    1992 Volume 78 Issue 4 Pages 572-579
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_572
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    An advanced mathematical model of a cold crucible capable of describing the fluid flow coupled with heat transfer limited by the free boundaries of free surface and a solidification front has been developed. Validity of the model was confirmed through measurements of a solidification front, surface velocity of the melt and surface temperature.
    Effect of parameters during operation, such as coil current, dome height and casting velocity on the fields of velocity and temperature has been investigated.
    Generally, two kinds of recirculation are expected to appear in the melt. They make a collision slightly above the contact point between the melt and the crucible wall. Appropriate geometrical relation between the dome height and the position of a coil exists to promote melting of scraps fed onto the dome.
    A titanium ingot consisting of completely melted scraps was continuously cast aided by the proposed operation condition obtained through the numerical calculation.
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  • Effect of Surface Roughness and Surface Material of Substrate on Initial Solidification Structure of 18Cr-8Ni Stainless Steel
    Hideo MIZUKAMI, Toshio SUZUKI, Takateru UMEDA
    1992 Volume 78 Issue 4 Pages 580-586
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_580
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    The effects of casting conditions as surface roughness and surface materials of the substrate, and pouring temperature on the solidification behavior and the structure of rapidly solidified 18Cr-8Ni stainless steel droplet samples have been studied. On the onset of the solidification, undercooling phenomena is observed. The undercooling linearly depends on the cooling rate, but does not on the casting conditions. Initial solidification length increases, and primary arm spacing and surface grain size decreases with increasing cooling rate. With very small cooling rate, solidification morphlogy changes from cell to dendrite. It presumably shows the change in the primary phase in the initial solidification.
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  • Mechanical Properties of Carbon Steels during Solidification
    Geon SHIN, Toshiyuki KAJITANI, Toshio SUZUKI, Takateru UMEDA
    1992 Volume 78 Issue 4 Pages 587-593
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_587
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    A technique for tensile tests has been developed for the investigation of mechanical properties of carbon steels during solidification. The equipment enables the test piece to melt and solidify without a crucible at a predetermined cooling rate. The tensile strength and ductility of Fe-C-1 mass% Mn samples have been measured during and after solidification. Temperature Range of Strength Generation (TRSG) during solidification is determined. It has been verified that ZST (Zero Strength Temperature), the maximum temperature showing the strength of sample by the tensile loading is different from ZDT (Zero Ductivity Temperature), the temperature showing the brittle-ductile transition. These mechanical properties of steels have been examined in relation with solid fraction which is evaluated from numerical analysis for micro-segregation during solidification, TRSG is the temperature range where solid fraction is 0.6-0.8, ZST is the temperature at which the solid fraction 0.6-0.7, and ZDT is about 1. The influence of carbon contents on the tensile strength of sample has also been studied.
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  • Quantitative Analysis of Laves Phase and Carbide in High Cr Heat Resistance Ferritic Steels
    Hiroyuki KUTSUMI, Atsushi CHINO, Youichi ISHIBASHI
    1992 Volume 78 Issue 4 Pages 594-600
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_594
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    A method for quantitaive analysis of Laves phase and M23C6 type carbide in high Cr heat resistance ferritic steel has been estab lished, and precipitation behavior of the Laves phase and carbide in these steels were investigated. The results obtained are as follows.
    (1) The Laves phase and carbide are quantitatively extracted by potentiostatic electrolysis in 10% AA-1% TMAC-methanol electrolyte or in 10 %HCl-methanol electrolyte.
    (2) Only the Laves phase in the residues extracted by above electrolysis can be dissolved in 0.5% Br2-methanol solution at 20°C for over 90 minutes. Consequently, the amount and chemical composition of the Laves phase and carbide can he determined by analysis of this treatment solution and the residues respectively.
    (3) The amount of the Laves phase increased with an increasing of aging time, while the amount of carbide remained constant.
    (4) The chemical composition of the Laves phase and carbide were independent of aging time, and approxiamately constant.
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  • Anodic Dissolution of Zinc in Chloride Solution
    Kimitaka HAYASHI, Yasuhiko MIYOSHI
    1992 Volume 78 Issue 4 Pages 601-607
    Published: April 01, 1992
    Released on J-STAGE: May 07, 2010
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_601
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    It was investigated that the kinetic parameters on the anodic dissolution mechanism of zinc in chloride solution with the measurement of anodic polarization. The following results were found.
    (1) The reaction rate of zinc anodic dissolution is proportional to the third order against the concentration of Cl- ion and to the zero order against that of OH- ion in the neutral solution (pH=58). In this case, it is found that the Tafel slope of i (current density) -φ(potential) curve is nearly eqml to 17 mV/decade. That is, the concentration of Cl- ion gives a great effect to the reaction of zinc anodic dissolution in the neutral solution.
    (2) The reaction rate of zinc anodic dissolution is proportional to the zero order against the concentration of Cl- ion and to the third Order against that of OH- ion in the alkali solution (pH=12.513.5). In this case, it is found that Tafel slope of i-φ curve is nearly equal to 40mV/decade. That is, the concentration of OH- ion has great influence on the reaction of zinc anodic dissolution, which is unaffected by that of Cl- ion, in the alkali solution.
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  • Durability of WC/Co Sprayed Coatings in Molten Pure Zinc
    Tomoki TOMITA, Yasuyuki TAKATANI, Yoshihumi KOBAYASHI, Yoshio HARADA, ...
    1992 Volume 78 Issue 4 Pages 608-615
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_608
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    In order to develop protective contings for sink rolls used in a coatinuous hot-dip galvanizing, sprayed cermet coatings were formed on a mild steel by High Velocity Flame Spraying system using two commercially produced WC-12 mass% Co powders and their durability in molten pure zinc(703783 K) have been studied by SEM, XRD, EDX and hardness tester.
    It was found that the durability of WC/Co sprayed coatings in molten pure zinc depended on the binding phases, which varied according to a powder-preparation process. Namely, the binding phase in WC/Co sprayed coatings made of powders prepared by a Spray-dried process ( SD-coating) mainly consisted of β-Co phase, but that prepared by a Sintered & Crushed process (SC-coating) mainly consisted of η-phase (Co3W3C and Co6W6C). In case of SD-coating, the binding phase, β-Co, dissolved into molten pure zinc so that the thickness has decreased in a short time. Though, in case of SC-coating, a Zn-rich and Co-poor layer was build up under the surface and the hardness dropped to HV 5001000 just below the surface, no changes of the thickness and microstructures have been observed for a long time.
    The appearant activation energy for the growth of Zn-invaded layer in SC-coating was 170 kJ/mol, which was nearly equal to that for dissolution of β-Co. It was suggested that a small amount of β-Co was also contained in SC-coating and such a excellent durability must have been obtained due to the different distribution manner of β-Co.
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  • Prediction of Multiplying Factor of Molybdenum and Hardenability of Fe-C-Mo Alloys with a Correction of Insoluble Carbide
    Tsuyoshi INOUE
    1992 Volume 78 Issue 4 Pages 616-623
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_616
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    Hardenability of Fe-C-Mo alloys varies to a larger extent with carbon and molybdenum contents, and with quenching temperature, and this is attributed to the variation in effective molybdenum and carbon due to insoluble carbides. For this reason, it is important for molybdenum hardenability to be evaluated by net amount of effective molybdenum with a correction of insoluble carbide.
    In this study, basing on the previously reported data, multiplying factor of molybdenum is derived as a function of effective molybdenum, [Mo]( % ), for Fe-C-Mo alloys containing molybdenum up to 2%:
    fMo=-0.512×[Mo]2+2.86×[Mo]+1
    Furthermore, prediction formulae calculating the amount of insoluble carbide remained on quenching as well as molybdenum and carbon fixed as carbide are proposed by a kinetic consideration of carbide dissolution at quenching temperature. Combining these formulae, hardenability of Fe-C-Mo alloys are calculated directly from chemical compositions and quenching conditions.
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  • Relationships between the Brittle Fracture Behavior of Deep-drawn Cups and Deformation Texture and Facet Unit
    Masatoshi SUDO, Tsuguaki OKI, Zenichi SHIBATA
    1992 Volume 78 Issue 4 Pages 624-631
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_624
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    1) The cleavage fracture can occur along the deep drawing axis of a cup which is deep drawn from a hot-rolled or cold-rolled steel blank. This cleavage fracture can be principally explained to be brought about with the increase in (200) pole density on the fracture surface. The work hardening and circumferential tensile residual stress can cause brittle fracture, but can not explain the whole fracture behavior.
    2) The reduction in the brittle fracture due to the increase in r value of blank sheet and additional ironing process can be caused by decreasing the (200) pole density on the fracture surfaces.
    3) The decrease in cleavage fracture unit (dc) which is closely related to the toughness, is in linear relationship with the decrease in the (200) pole density and grain size on the fracture surfaces.
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  • Effects of Hot Rolling Conditions on Hot Rolled Microstructures and Ridging Properties in 17% Cr Ferritic Stainless Steel
    Yoshihiro UEMATSU, Koichi YAMAZAKI
    1992 Volume 78 Issue 4 Pages 632-639
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_632
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    Effects of rolling temperature and inter-pass annealing on the microstructures of hot rolled and annealed strips and the ridging property of cold rolled and annealed sheet have been investigated of continuously cast slab of Nb added 17% Cr stainless steel which had a near {100}//N. D orientation.
    In such a case of no inter-pass annealing where no recrystallization during hot rolling occures, decrease in the rolling temperature increases deformation bands, and these banding makes recrystallized structures of hot rolled strip fine. When recrystallization occures by inter-pass annealing, microstructures of hot rolled strip become finer and uniform recrystallization occures after hot strip annealing.
    The ridging property of cold rolled and annealed sheet corresponds to the condition of recrystallization of hot rolled and annealed strip. When coarse unrecrystallized domaines remain in the center layer of annealed hot strip, it causes severe ridging in final annealed sheet. These results suggest that the unrecrystallized center layer of hot rolled and annealed strip retains strong {100} //N. D orientation and thereby deteriorates ridging properties of final annealed sheet. The suggestion is supported by another experiment of one pass hot rolling.
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  • Effect of Stress Amplitude Transient on Fatigue Crack Initiation and Propagation of High Strength Steel in Synthetic Sea Water under Cathodic Protection
    Norio MARUYAMA, Masae SUMITA
    1992 Volume 78 Issue 4 Pages 640-646
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_640
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    The effect of varying stress on fatigue life under cathodic protection by a zinc sacrificial anode and freely corroding condition in synthetic sea water and in air was investigated using 800 MPa grade high strength steel notched specimens ( Kt= 3.5 ).
    The main results obtained are as follows:
    1) Under a constant stress amplitude (CSA), fatigue lives in sea water under cathodic protection are shorter than those in air. However, under two step stress amplitude (TSSA ), fatigue lives under cathodic protection are rather longer than those in air.
    2) In a low stress amplitude region, fatigue lives under TSSA are shorter than those under CSA in air and under cathodic protection.
    3) Even when the higher stress amplitude in TSSA is much lower than the values shown by the S-N curves under CSA, the failure of notched specimens occurs.
    4) Under the free corrosion potential, there is no difference in fatigue lives between under TSSA and under CSA, and Miners rule exists between them.
    5) Under TSSA, macroscopic crack growth rate is retarded in air and under cathodic protection, and the effect of TSSA on macroscopic crack growth is in reverse to that on crack initiation and microscopic crack growth.
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  • Fracture Behavior at Elevated Temperature of a 316 Stainless Steel with High Concentration of Helium Implanted
    Kazuya MIYAHARA, Akira ITOH, Hideo KAYANO, Yuzo HOSOI
    1992 Volume 78 Issue 4 Pages 647-649
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_647
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  • Precipitation and Growth of γ''-phase in Ni-15Cr-8Fe-6Nb Alloy
    Kiyoshi KUSABIRAKI, Shin-ichi ARAIE, Takayuki OOKA
    1992 Volume 78 Issue 4 Pages 650-657
    Published: April 01, 1992
    Released on J-STAGE: January 15, 2010
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_650
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    The nucleation and growth behavior of disc-shaped ordered γ''-phase and spherical ordered γ'-phase in Ni-base superalloys, modified Inconel X-750 type alloy (X-750M) and Inconel X-750 type alloy (X-750), has been investigated mainly by micro-Vickers hardness test and transmission electron microscopy. The hardness of X-750M aged in various conditions closely related to the size and the quantity of γ'' and δ-phases. Increasing the Nb content while decreasing the (Al+Ti) content in the alloys promoted the formations of γ'' and δ-phases. The growth kinetics of γ''precipitates in the region free of δ-phase followed the prediction of Lifshitz-Slyozov-Wagner theory of diffusion controlled growth at all aging temperatures. The activation energy of the growth of γ'' precipitates in X-750M was estimated to be 397 kJ/mol.
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  • Microstructures and Partitioning Ratios of Alloying Elements in Rhenium Containing Nickel-based Single Crystal Superalloys
    Kazuhiro MATSUGI, Shogo MIYAZAKI, Yoshinori MURATA, Masahiko MORINAGA, ...
    1992 Volume 78 Issue 4 Pages 658-665
    Published: April 01, 1992
    Released on J-STAGE: May 07, 2010
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_658
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    In order to obtain some criteria for determining the optimum compositions of rhenium (Re) containing nickel-based single crystal superalloys, the phase stability and the partition ratios of alloying elements between γ and γ' phases were investigated using the Ni-10Cr-12Al-1.2Ti-2.6Ta-2.0W-0.7Mo-01Re (mol%) alloys. Most of Re atoms were found to be distributed mainly in the γ phase and alter significantly the partition ratios of the other elements between γ and γ' phases. It was shown that the decrease of Cr, Ta, W, Mo contents and the increase of Al content were most desirable in the design of alloys containing more than 0.25 mol % Re. Further, in order to investigate the possibility Co addition into the Re containing alloys, its effects on the phase stability and the partition ratios of elements were examined with the Ni-10Cr-12Al-1.5Ti-2.1Ta-2.3W-0.8Mo-0.25Re(mol %) alloys in which 09mol % Co was substituted for Ni. It became evident from the present experiment that the Co substitution for Ni did not induce any large changes in the phase stability and also in the partition ratios of the alloying elements in this system.
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  • Correlation of Ta/W Compositional Ratios with the High Temperature Properties of Ni-Cr-Al-Ta-W(-Co) Single Crystal Superalloys
    Kazuhiro MATSUGI, Yoshinori NURATA, Masahiko MORINAGA, Natsuo YUKAWA
    1992 Volume 78 Issue 4 Pages 666-672
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_666
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    The optimum Ta/W compositional ratio was searched for in Ni-10/11 mol % Cr-12/14 mol% Al -Ta-W( -5mol% Co) alloys in order to get an excellent combination of creep-rupture, phase stability and hot-corrosion resistance in a Na2SO4-NaCl salt. Solidification and precipitation temperatures were also examined as a function of the Ta/W ratio. The γ' solvus temperature and the creep-rupture life were found to increase with increasing Ta/W ratio up to 1.0. However, when the ratio exceeded 1.0, the creep-rupture life reversely decreased probably due to the increase in the residual amount of the eutectic γ' phase in alloys. On the other hand, hot-corrosion resistance increased monotonously with the Ta/W ratio. From the present study it was concluded that the Ta/W compositional ratio of 0.5 to 1.0 was most suitable for balancing the high temperature properties in this alloy system.
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  • In-situ SEM Observation of Tensile Fracture in Ti-13V-11Cr-3Al Alloy
    Naotake NIWA
    1992 Volume 78 Issue 4 Pages 673-679
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_673
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    The deformation and fracture behavior of the aged microstructure of Ti-13V-11Cr-3Al alloy was studied by SEM in-situ observation. Comparing with beta matrix, the areas where alpha phase precipitates i.e. alpha colonies and the neighborhoods of grain boundaries show higher resistance to deformation. Thus, strength becomes higher by increase of alpha precipitates with aging. In the fracture of this alloy, a main crack propagates with forming microcracks within alpha colonies and along grain boundaries ahead of the main crack and joining them. The crack propagation along grain boundaries is faster and less ductile than the transgranular crack propagation following microcracks in alpha colonies. With development of aging, the grain boundary cracking becomes prevailing as a fracture mechanism, hence, ductility reduces notably. Alpha precipitates play an important role not in strengthening but also in fracture of this alloy.
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  • TiAl Melting in CaO Crucible and Its Mechanical Properties
    Nobuo SAKUMA, Tatsuro MITSUI, Hyojiro KURABE, Tokuzo TSUJIMOTO
    1992 Volume 78 Issue 4 Pages 680-687
    Published: April 01, 1992
    Released on J-STAGE: May 29, 2009
    DOIhttps://doi.org/10.2355/tetsutohagane1955.78.4_680
    JOURNAL FREE ACCESS
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    Titanium and its alloys are conventionally melted in watercooled copper hearth to avoid the chemical reaction between crucible and molten metal. However, titanium activity in TiAl is supposed to be low. This study was carried out to prove the possibility of vacuum-induction melting of TiAl alloys in high-purity CaO crucible. The following results were obtained.
    (1) Oxygen contents in TiAl were always 0.110.14 wt% corresponded to thermodynamical equilibrium value when about 800 g was melted. This amount was a little larger compared with 0.04 wt% in plasma-arc melted TiAl. (2)Small amounts of 0.130.15 vol% of CaO inclusions with the sizes of 15μm were contained in TiAl, being nearly equal to killed steels. (3)New crucibles with 520 wt% CaF2 for preventing CaO-TiAl reaction, showed no effect for decreasing oxygen content, but a usefull effect for reducing inclusions due to the thermal stress relief by CaF2 film between CaO particles, resulting in long durabilities. (4) As-cast TiAl with compositions of 33.534.5 wt% Al showed elongations of 0.60.8% lower than plasma-arc melted TiAl. However, they were ameliorated to 1.1-1.4% by annealing at 900°C to 1200°C. This phenomenon can be explained from the point of veiw of the O diffusion from γ phase to α2 phase.
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