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Volume 48, Issue 6
Displaying 1-14 of 14 articles from this issue
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Kozo Nakazawa, Yoshikuni Kawabe1984 Volume 48 Issue 6 Pages 571-576
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to improve the susceptibility of ultrahigh strength maraging steels to hydrogen gas environment embrittlement, the application of electroplated nickel or copper coatings and electroless nickel-phosphorus coatings, and the effect of heat treatment after coating on the susceptibility to hydrogen embrittlement have been studied.
When the age-hardened steels were coated and then baked at 473 K, the notch tensile strength of nickel coated specimens in hydrogen gas was higher than that of uncoated specimens, and the thicker the coating, the higher the strength in the thickness range between 2.5 and 20 μm. The notch tensile strength of nickel-phosphorus coated specimens was equal to that of uncoated specimens.
When the unaged steels were coated and then heated at 773 K to make them age-harden, the steel-coating bond was well established compared with the specimens baked at 473 K. In the nickel coated specimens, the notch tensile strength depended on the thickness of coating greatly, that is, the hydrogen embrittlement was improved by 10-20 μm nickel coatings, whereas it was enhanced by 2.5-5 μm nickel coatings. The notch tensile strength of nickel-phosphorus coated specimens was lower than that of uncoated specimens. In the copper coated specimens, the relief of hydrogen that had been absorbed during plating was insufficient by heating at 473 K or 773 K, and the hydrogen gas embrittlement was enhanced by the coating, particularly, in the 773 K specimens.View full abstractDownload PDF (1612K) -
Kozo Nakazawa, Yoshikuni Kawabe1984 Volume 48 Issue 6 Pages 577-582
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to make clear the abnormal phenomenon that the notch tensile strength of ultrahigh strength maraging steels is lowered by nickel or copper coating in hydrogen gas atmosphere, the effect of the residual stress of the coating layer on the embrittlement behavior has been investigated.
Specimens that had been heated at 773 K after coating showed the enhanced embrittlement by the coatings, and the residual stress before tensile testing was tensile and approximately equal to the yield stress of the coatings. When the residual stress had been shifted toward compressive stress by preloading for nickel coated specimens or by subzero cooling at 77 K for copper coated specimens, the strength of nickel coated specimens became higher than that of the uncoated ones, i.e., a positive effect of the coating was observed. The strength of copper coated specimens also increased by the shift of residual stress, although it was lower than that of the uncoated ones due to an inadequate relief of internal hydrogen that had been absorbed into the specimens during electrodeposition. The enhancement of hydrogen gas embrittlement by the coatings was explained in terms of both the hydrogen absorption at the fresh surface that was producecl by the plastic deformation from the early stage of loading and the residual stress that controlled the beginning of plastic deformation of the coatings.View full abstractDownload PDF (1025K) -
Osamu Yanagisawa, Tetsuo Yano, Takayuki Sagahara, Masanobu Ohmori1984 Volume 48 Issue 6 Pages 583-588
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSWork-hardening behavior of Al-Al3Ni eutectic composites in stage II was investigated at various temperatures by studying tensile deformation behaviors and the Bauschinger effect.
The work hardening rate of this material in stage II at temperatures from 293 K to 673 K, which was measured by a simple tensile test, decreases with rising temperature. Even at elevated temperatures the contribution of elastic modulus of Al3Ni fibers to the strain hardening rate is predominant. The matrix of this composites shows a linear work hardening at temperatures from 293 K to 673 K, but its contribution to the strain hardening rate of composites is very small.
The mean internal stress and the reversibile stress of this composites, obtained by a cyclic tensile loading-unloading test, are consistent with the elastic stress component of the fibers and the reversibile stress in the matrix, respectively. This result suggests that the Bauschinger effect in the matrix is very small, even if it exists, and the stress causing the Bauschinger effect is predominantly the elastic component of fibers.View full abstractDownload PDF (716K) -
Ryuta Onodera, Michio Hirokado, Mineo Shimizu1984 Volume 48 Issue 6 Pages 589-594
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSRadial direction fracture, named concerning the fracture surface with a radial pattern, is a kind of tensile fracture of round bar specimen and often observed in tempered steels. The present work studied the morphology of the fracture surface and the condition of occurrence of the R-D fracture. Scanning electron microscopic observations showed that the R-D fracture surface consisted of shear fracture plane inclined by 45° to the tensile axis and vertical fracture plane parallel to the tensile axis. The microstructures of the shear and the vertical plane were dimple pattern and low ductility shallow dimple pattern, respectively. The R-D fracture occurred prominently in 0.35-0.45C steels tempered at 773-873 K and became less prominent with increase and decrease of carbon content and tempering temperature. Steels annealed, normarized and isothermally transformed showed the cup and cone fracture only.
These experimental results mean that it is necessary to the R-D fracture that spherical carbides of moderate size disperse properly in the specimen. Accordingly the cause of the R-D fracture might be attributed to rows of elongated voids which were formed about the carbides and arranged along grain boundaries of tempered martensites, because the vertical plane with high density of void would be liable to crack by the lateral stress induced at a macroscopic crack tip.
Both a quenched and a furnace cooled S35C specimen after tempered at 973 K for 1.8 ks showed the R-D fracture. On the contrary, both a quenched and a furnace cooled specimens tempered for 72 ks showed the cup and cone type fracture. These results suggest that temper brittleness does not play an important role in the occurrence of the R-D fracture.View full abstractDownload PDF (2250K) -
Shiro Ban-ya, Mitsutaka Hino1984 Volume 48 Issue 6 Pages 595-603
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA.C. Impedance method has been applied to reactions between aquous solution and metal in the field of corrosion science. There has been, however, only a little application of this method to the reactions, like molten salt-metal electrode reactions, at elevated temperatures because of difficulty in the experiments.
In the present study, impedance measurements of sodium silicate-platinum electrode reaction have been made by A.C. impedance method in the frequency range from 5 Hz to 100 kHz. The electrolyte resistance of the slag has been considered together with the double layer capacitance, charge-transfer overvoltage at the interface, reaction overvoltage and diffusion overvoltage in the slag. The overpotential of platinum in the slag was kept at values ranging from −0.6 to +0.6 V against platinum crucible which was a counter electrode. The experiments were carried out at 1200 to 1500 K under an argon atmosphere. The frequency response of complex impedance of the electrode reaction consisted of a semicircle at high frequencies and a straight line with a slope of 45° at low frequencies.
The conductivity of the melts increased slightly with increasing Na2O concentration and temperature. The reacting species have not been clarified, but the charge-transfer resistance for both of anodic and cathodic reactions obtained from the radius of the semicircle decreased markedly with increasing temperature. The double layer capacitance increased with increasing temperature and depended strongly on the electrode potential. The mass transfer process, therefore, would behave as a rate-control step at higher temperatures.View full abstractDownload PDF (1334K) -
Tetsuji Noda, Toshio Kainuma, Masatoshi Okada1984 Volume 48 Issue 6 Pages 604-610
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMolybdenum was purified by arc-melting in Ar-H2 (H2: 0-30 vol%) gas mixture. The impurity content in the ingots was measured by chemical methods and Auger electron spectroscopy. The mechanical properties of the cast molybdenum was evaluated by a bend test and an impact compression test in the temperature ranges from 200 to 1223 K and from 473 to 780 K, respectively.
A molybdenum ingot with a purity of about 99.99 mass% was obtained by the arc-melting in gases containing hydrogen. However, when the hydrogen concentration in the atmosphere exceeded about 10 vol%, the DBTT of the ingot abruptly increased. This increase was considered to be caused by the excessively dissolved hydrogen during the melting. The ingot melted in the gas mixture of which hydrogen concentration was less than 5% nearly has the same DBTT as that by electron-beam melting. Such ingots could be worked without cracks along grain boundaries at 570 K.View full abstractDownload PDF (1834K) -
Shigeru Yonetani, Hisakimi Notoya, Yuzo Takatsuji1984 Volume 48 Issue 6 Pages 611-617
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSResidual stresses in a high hardness specimen ground in various grinding conditions were measured, and the effects of various causes relating to the occurrence of residual stress were investigated. Specimens of S45C, SCM4, SNCM8, SK3, SUJ3 and SKS2 were prepared and these specimens were hardened to several ranges from Rockwell hardness HRC 30 to HRC 60 by quenching and tempering. As a result of this experiment, it is shown that the magnitude and distribution of grinding residual stress in high hardness specimens were greatly affected by the volume change due to tempering in grinding, and correlations between maximum residual stress and grinding temperature have linear relations which are characteristic for hardness of each specimen.View full abstractDownload PDF (1073K) -
Koji Tanoue, Osamu Nakano, Hisatoshi Mori, Hidehiko Matsuda1984 Volume 48 Issue 6 Pages 618-625
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSubsequent fabrication of powder metallurgy tungsten rods becomes often difficult because of their brittle fracture in the swaging process. Workable and unworkable lots are sampled to investigate the cause of brittleness in the paractical swaging process of 2.5 mm in diameter. While the fiber structure is well grown to be almost straight in the workable lots, it consists of many discotinuous arrays of wavy fibers in the unworkable ones. There is no direct relation between the workability and the segregation of impurities (O, C) to the boundary of fibers. The deflection to fracture in bending tests reflects the workability well, and the ductility is considerably improved by electropolishing the surface. Tensile tests shows that there is an intrinsic difference in the internal structure between the two lots, which may be caused by different degrees of the development of fiber textures. It is concluded from the results that the practical workability in the swaging process depends on the degree of texture development as well as the roughness of the surface.View full abstractDownload PDF (2527K) -
Kiyoshi Ichikawa, Yoshiji Kinoshita, Shoji Shimamura1984 Volume 48 Issue 6 Pages 626-632
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAn investigation is reported on the grain refinement of Al-Cu alloys including 4, 10 and 24 mass%Cu by the vacuum rheocasting with higher rotation speeds of a stirrer up to 23 rev/s applied during the solidification under continuous furnace cooling. The results are as follows. The sizes of primary solid particle in these alloys are consistently decreased with the increase in rotation speed of 13-23 rev/s. The minimum sizes of primary solid particle at 23 rev/s are 133±32 μm in Al-4%Cu, 121±44 μm in Al-10%gCu and 120±51 μm in Al-24%Cu. They are also decreased with the cooling rate at which they are cooled down to their liquidus temperatures. The increased rotation with the stirring of semi-solid makes the grain structure finer, showing the change in morphology from rosette-type to spherical one. It is thus expected that the mechanical grain refinement during the solidification of an alloy can be established by the higher rotation of a stirrer inserted in the solid-liquid coexisting zone of it, since the dendrites formed are destroyed into non-dendritic primary solid particles by shearing operation with the rotation of stirrer. The coarsening of primary solid particles (grain growth) under the fluid flow is theoretically examined on the basis of the experimental results to obtain the mixing diffusivity.View full abstractDownload PDF (1761K) -
Hiromasa Takeuchi, Naomi Nishi1984 Volume 48 Issue 6 Pages 633-639
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDroplets of Al-0∼5.7 mass%Cu alloys were dropped on a chill block made of pure copper, cast iron and stainless steel. The heat transfer during solidification of droplets was calculated using the heat balance equation. The external surfaces of droplets solidified were examined by optical microscope.
The degree of supercooling of droplets decreased with increasing solute content and superheat of molten metal. The number of discs increased with increasing solute content and superheat. The degree of supercooling and the number of discs became large in order of stainless steel, cast iron and pure copper. The concentration of copper in the disc increased with increasing degree of supercooling. The effective distribution coefficients of Al-4.5 mass%Cu alloy varied from 0.20 to 0.40 with changing degree of supercooling from 7 K to 32 K. The relation between the growth rate of disc (R) and the degree of supercooling (ΔTC) was expressed as R∝(ΔTC)1.5.View full abstractDownload PDF (2096K) -
Satoru Ohno, Masahiro Uda1984 Volume 48 Issue 6 Pages 640-646
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to make clear the generation mechanism of ultrafine metal particles by “hydrogen plasma-metal” reaction (new method to produce ultrafine metal particles), a study has been made of the measurement of generation rate of particles from 16 metals such as Ag, Al, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pd, Sc, Si, Ta, Ti, V and W by arc melting of these metals in the 50%H2-50%Ar atmosphere at 0.1 MPa pressure.
It was found that the generation rate of above metals decreases in the following order: Mn, Ag, Al, Sc, Cr, Si, Pd, Fe, Cu, Ti, Ni, V, Mo, Ta and W. The driving force for the generation of particles from metals is much concerned with factors of the heat of vaporization of metals, the heat of formation for recombination from atom (dissolved in metal) to molecule (evolved into gas phase) of hydrogen and the melting point of metals.View full abstractDownload PDF (1530K) -
Hiroshi Tanaka, Masaru Sato1984 Volume 48 Issue 6 Pages 647-654
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTo find out optimum tube-drawing conditions for correcting the wall-thickness deviation by floating plug and also to ascertain if the oscillatory plug movement can cause the thickness variance, phosphor deoxidized copper tubes were drawn using floating plugs in various conditions. The following conclusion has been obtained: (1) Both die and plug semi angles influence the concentricity and lengthwise wall-thickness accuracy of the tube. The drawing speed seems to have no effect except when it is too slow. (2) The optimum die and plug semi angles (α and β) used by the experiments for correcting the wall-thickness deviation are: α=13° and β=10°, 11°. (3) By certain combinations of die and plug semi angles the oscillatory plug movement increases the lengthwise wall-thickness deviation and decreases the tube concentricity. (4) For obtaining a tube of circumferencially and lengthwise uniform wall-thickness, the consecutive drawings with combinations of α and β given in (2) are desirable.View full abstractDownload PDF (1030K) -
Makoto Sugamata, Junichi Kaneko, Ken-ichiro Aoki1984 Volume 48 Issue 6 Pages 655-661
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe influence of final thermomechanical treatment (FTMT) on the age-hardening behavior of Al-Cu-Mg alloys containing varied Mg/Cu atomic ratios has been studied. Measurements of hardness and electrical resistivity as well as transmission electron microscopy were carried out on both FTMT and T 6 materials. From the age-hardening curves, the amount of age-hardening attained at the peak hardness was evaluated on FTMT specimens.
For each alloy specimen, the peak hardness of the FTMT material in the final aging is higher than that of T 6 material. The amount of age-hardening attained in the FTMT material is higher than that of the T 6 material in the case of alloys with Mg/Cu atomic ratio greater than 0.7, whereas it is lower for alloys with this ratio below 0.5. The age-hardenability of FTMT materials decreases, when the amount of cold working is increased from 10 to 30%, regardless of Mg/Cu ratio. Electron microscopy of FTMT materials at their peak hardness revealed that the precipitates of the S′ intermediate phase are formed on dislocation lines more finely and uniformly than those of the θ′ phase. Such fine and uniform distribution of S′ phase is thought to enhance the age-hardenability of FTMT materials in alloys of Mg/Cu atomic ratio above 0.7.View full abstractDownload PDF (1786K) -
Teruo Takahashi, Yasuhiko Hashimoto, Shinichiro Omori, Koichiro Koyama1984 Volume 48 Issue 6 Pages 662-668
Published: 1984
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDilute Cu-Al, Cu-Ti and Cu-Al-Ti alloys internally oxidized over the temperature range 1073-1323 K were investigated by X-ray diffractometry, optical and electron microscopy and microvickers hardness testing.
From X-ray diffractometry of the nitric-acid-treated residues, γ Al2O3, α Al2O3 and CuAlO2 in internally oxidized Cu-Al alloys and anatase and rutile type TiO2 in internally oxidized Cu-Ti alloys were identified, respectively. In internally oxidized Cu-Al-Ti alloys, all of the oxides observed in above both Cu-Al and Cu-Ti systems were identified, and other complex oxides were not detected.
By electron microscopy, it was revealed that the dispersion oxide particle size was remarkably decreased with addition of small amount of titanium into Cu-Al alloys. In accord with results from electron microscopy, the microvickers hardness increased with the ratio of TiO2 to whole oxide.
The internally oxidized Cu-Al-Ti alloys possessed excellent qualities that beloned to the internally oxidized Cu-Al and Cu-Ti alloys.View full abstractDownload PDF (1895K)
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