Journal of the Society of Materials Science, Japan
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
Volume 36 , Issue 404
Showing 1-16 articles out of 16 articles from the selected issue
  • 1987 Volume 36 Issue 404 Pages 424-430
    Published: May 15, 1987
    Released: June 03, 2009
    JOURNALS FREE ACCESS
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  • Yoshio KITSUNAI, Yutaka MAEDA
    1987 Volume 36 Issue 404 Pages 431-436
    Published: May 15, 1987
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    Failure analysis for a reduction gear and bolts failed by fatigue was carried out by means of fractography, and the values of stress amplitude during service were estimated using a relation between striation spacing and stress intensity factor range, ΔK. The failed reduction gear had been used for a hoist with a rated load of 5 tonf attached to a travelling crane, and fatigue cracks initiated from the root of teeth. The bolts had been used for connection of slewing circle and counter weight of a truck crane. Metallurgical examination, fatigue test and calculation of applied stress were also performed to clarify the failure causes. The stress distributions of 32 high strength bolts of 20mm diameter on a slewing circle were measured by strain gauges mounted on the bolts, and the measurement was carried out using the same type of track crane as the failed one.
    The value of stress amplitude evaluated from the striation spacing was found to be almost equal in stress to that of the result of calculation or actual measurement of stress. Therefore the combined fractographic-fracture mechanics method was found very valuable in the quantitative analysis of fatigue failure of machine parts. The failure cause of the gear was related to the lack of hardness of tooth root. The fatigue limit of the bolts was 4.8kgf/mm2. The couse of failure for the bolts was due to overload during operation. Moreover, a high stress concentration for few bolts in the slewing circle may also be related to the failure cause.
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  • Hisakichi SUNADA
    1987 Volume 36 Issue 404 Pages 437-442
    Published: May 15, 1987
    Released: June 03, 2009
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    An investigation was conducted to find the effects of the thermomechanical processing developed by O.D. Sherby and his coworkers on the tensile and impact strengths of high carbon steels with Cr or Mn. Billets were warm-rolled at about 470K repeatedly to reduce their thickness from 70mm to 6mm. Tensile tests were performed at room temperature and Charpy impact tests were done between 194 to 473K. Observations of fracture patterns of the tensile and impact fractured surfaces were made by using scanning electron microscopy.
    The results obtained are as follows:
    (1) The processing gave fine spheroidal carbide particles and a ferrite matrix, and the sizes of grains and carbide particles increased with increasing carbon content.
    (2) The tensile strength of 1.27% C steel with forged structure was slightly higher than that with rolled structure. A steel containing Mn had higher strength, and its elongation of 7% was improved up to 45% by solid solution treatment.
    (3) The impact strength of forged steel was improved greatly by warm rolling. Although a steel containing Cr was not improved by water toughening, a steel containing Mn increased its impact value by water toughening.
    (4) Fractographs of the tensile fractured surface of rolled steel showed fine dimples, seemingly associated with ductility. The distribution of voids in the area near ferrite structure was little denser than that near austenite structure.
    (5) The impact fractured surface of a steel containing Mn exhibited smaller dimples than its tensile fractured surface.
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  • Haruo NAKAMURA, Hideo KOBAYASHI
    1987 Volume 36 Issue 404 Pages 443-447
    Published: May 15, 1987
    Released: June 03, 2009
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    Fracture toughness tests were conducted for an A533B-1 steel by using chevron-notched compact specimens in the temperature range from the lower shelf regime up to the transition temperature in order to assess the R-curve for cleavage fracture. The applicability of these specimens to the simple fracture toughness test without introducing fatigue pre-cracks was examind. The following are the summary of the results obtained.
    (1) The fracture toughness test by using the chevron-notched specimen gave an overestimated value due to the absence of stable crack growth by cleavage from the notch tip. The difficulty of introducing pre-cracks by cleavage suggests that the fracture resistance for crack initiation by cleavage is considerably higher than that for crack growth by the same fracture mechanism.
    (2) By introducing fatigue pre-cracks to the chevron-notched specimen, the fracture toughness value can be evaluated accurately at the lower shelf regime. At the transition temperature, however, it is overestimated, the reason of which should be attributed to the thinner effective thickness along the pre-crack front of the chevron-notched specimen compared with that of the conventional throughthickness cracked specimen.
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  • Kazumune KATAGIRI, Masahiko FUKUMOTO, Kazuo KOYANAGI, Shigehiro NISHIJ ...
    1987 Volume 36 Issue 404 Pages 448-454
    Published: May 15, 1987
    Released: June 03, 2009
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    Strain effects and mechanical properties of several practical superconducting wires at cryogenic temperatures were investigated. The results were discussed in the light of morphology of fracture surface.
    The NbTi wire showed ductile deformation behavior until fracture in tensile tests even at liquid He temperature. Fatigue cracks were initiated within CuNi sleeve at the surface layer of the wire, especially from inclusions in it. The excellent fatigue behavior is attributed to the hardened microstructure of the CuNi layer.
    The critical current Ic of Nb3Sn wires, especially bronze processed, was sensitive to strain. The reversibility of Ic to the strain was limited by cracking in the Nb3Sn filaments. The in-situ processed wire, consisted with ultra-fine filaments, showed excellent mechanical properties and Ic vs. strain characteristics as compared with those in the bronze processed. Both the mechanical properties and the Ic vs. strain characteristics changed with wire structure and heat treatment. Fatigue cracks initiated within the brittle Nb3Sn intermetallic compound layer. They appeared to connect each other gradually and propagate through ductile constituents at the final stage of fracture.
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  • Masahiro SHIKIDA, Yukio KANAYAMA, Hideaki NAKAYAMA
    1987 Volume 36 Issue 404 Pages 455-461
    Published: May 15, 1987
    Released: June 03, 2009
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    Two types of compacted vermicular graphite (CVG) cast iron having ferritic and pearlitic structures have been studied to determine the effects of CVG on fatigue strength, fatigue crack growth rate and fracture appearance of cast iron. The results obtained were compared with those of two types of spheroidal graphite (SG) cast iron (corresponding to JIS FCD) having ferritic and pearlitic structures. The significant conclusions obtained are as follows: The fatigue limit of the CVG cast iron was lower than that of the SG cast iron independent of matrix structure. This tendency was prominent for ferrite matrix. However, the fatigue limit ratio of the CVG cast iron was not less than that of the SG cast iron regardless the shape of graphite. The fatigue crack growth rate of the CVG cast iron was higher than that of the SG cast iron. This trend was significant for the CVG cast iron having ferritic matrix. This could be due to the fact that the fatigue crack propagation in the CVG cast iron occurs through a zig-zag path between graphites more than that in the SG cast iron when compared at the same level of Kmax.
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  • Akio OTSUKA, Keiichiro TOHGO, Hiroto SUGAWARA, Fumihiro UEDA
    1987 Volume 36 Issue 404 Pages 462-468
    Published: May 15, 1987
    Released: June 03, 2009
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    A fractographic study on fatigue of WC-12% Co hardmetal under tension-compression loading was made by using SEM and EDX at various stress ratios, namely, R=0, -1, -4, -9 and -∞ (compression fatigue), where R is the stress ratio σminmax. Under R=0 and -1, fatigue cracks were initiated from the inside of the specimen, where cleavage fracture and high concentration of Co were always found. These results seem to suggest that the fatigue cracks in these cases were initiated from the cleavage of hcp Co transformed from fcc Co existing in the as-sintered state, due to cyclic straining. On the other hand, in compression fatigue (R=-∞) and tension-compression fatigue (R=-4, -9), in which σmax is lower than the fatigue limit in tensile fatigue (R=0 and -1), fracture was initiated from the surface of the specimen. The fracture origins in these cases were grooves formed by the dropping of the surface layer of the specimens. In these cases (R=-4, -9 and -∞) no concentration of Co was found by EDX in the area of fracture initiation.
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  • Kazutaka FUJITA, Ryoichi KOTERAZAWA
    1987 Volume 36 Issue 404 Pages 469-475
    Published: May 15, 1987
    Released: June 03, 2009
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    Propagation of microscopic fatigue cracks by periodic overstressing was studied with quenched and tempered 0.45% C steel. Acceleration of crack propagation occured in 0.45% C steel as in the case of 0.15% C steel previously reported, when the crack length was more than 50μm. The lower limit of understress that caused such an acceleration was reduced steeply as the crack length became longer. The acceleration in 0.45% C steel was less than in 0.15% C steel in accordance with the previous result on macroscopic cracks in which the acceleration was less in materials of higher strength. In the cases of short cracks (below 200μm) and long cracks (above 200μm) loaded with low understress, the microscopic fracture surface consisted of small facets, which were supposed to be related to the crystal structure of steel, and cracks observed on the specimen surface propagated intermittently, suggesting that microstructure had a significant effect upon crack propagation under intermittent overstressing. In the case of long cracks loaded with high understress, the microscopic fracture surface consisted of large facets and cracks propagated steadily, indicating that microstructure had less effect. No appreciable difference was observed in crack opening behavior before and after overstressing, and the acceleration of crack propagation was not likely to be related to the crack closure phenomenon.
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  • Yoshihiko MUKAI, Masato MURATA
    1987 Volume 36 Issue 404 Pages 476-481
    Published: May 15, 1987
    Released: June 03, 2009
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    The mechanism of stress corrosion cracking (SCC) of duplex stainless steel, SUS 329J1 was investigated in 42% MgCl2 aq. sol. (416K) by studying the effect of structural anisotropy on SCC. It was made clear that SCC was more pronounced in the case of crack growth being parallel to the main rolling direction than in other cases, and cracks tended to propagate along α phase than γ phase. The high SCC resistance of SUS 329J1 duplex stainless steel seems to be caused by cathodic protection of γ phase for α phase.
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  • Hitoshi UCHIDA, Keiji KOTERAZAWA, Hitoshi OSHIRO
    1987 Volume 36 Issue 404 Pages 482-487
    Published: May 15, 1987
    Released: June 03, 2009
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    The susceptibility to stress corrosion cracking (SCC) in boiling 42% MgCl2 solution was examined crystallographically for the cold worked SUS 304 steel single crystals with two tensile axis orientations.
    The susceptibility to SCC of cold worked single crystals was dependent on tensile axis orientation: The threshold stress for SCC occurrence in the single crystal of multiple slip system was lower than that of single slip system. In this case, the crack initiation of both single crystals was suppressed by cold-working. Once that the cracks initiated, however, they propagated rapidly. The fracture surface of SCC was formed by the macroscopic crack growth along ‹110› direction on {100} plane, regardless of tensile axis orientation. However, the microscopic crack morphology was influenced by tensile axis orientation, which was characterized by plate-like pattern: The stereo analysis technique revealed that the macroscopic {100} plane was composed of the crack planes along primary slip plane and conjugate slip plane in the single crystal of single slip system, while along four equivalent {111} planes in that of multiple slip system.
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  • Kenjiro KOMAI, Kohji MINOSHIMA, Mitsuhiro YASUMURA
    1987 Volume 36 Issue 404 Pages 488-494
    Published: May 15, 1987
    Released: June 03, 2009
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    SCC crack growth behavior under dynamic mixed mode loading conditions was investigated in a high-strength Al-Zn-Mg alloy immersed in 3.5% NaCl solution. Mode II dynamic loads including high frequency (30Hz) small vibratory loads at a high stress ratio of 0.95 (dynamic SCC) and low frequency (0.002-5Hz) variation at a stress ratio of 0.1 (cyclic SCC) were applied to specimens with superposition of static Mode I loads of KIS=10MPa·m1/2 larger than the crack opening stress intensity factor and KIS=30MPa·m1/2 larger than the Mode I static SCC threshold, KISCC. In the case of static and dynamic Mode II SCC tests, crack extension was not observed; oblique cracks at an angle of about 50-60 degrees against the direction of shear stress were initiated and propagated, which was dominated by Mode I intergranular dissolution. On the other hand, subcritical Mode II cyclic SCC crack extension was observed at high ΔKII levels with higher crack growth rates than dry air values. The enhancement of crack growth rate was dependent on the values of Mode I static loads and Mode II stress cycle frequency: the increase in crack growth rate from the dry air value at KIS=10MPa·m1/2 was larger than that at KIS=30MPa·m1/2, and had maximum at a stress cycle frequency of 0.1Hz. In the case of Mode II fatigue, transgranular failure including elongated dimples and slips was dominant, whereas transgranular dissolution in addition to those observed in Mode II fatigue existed. The fraction of transgranular dissolution fairly well corresponded with an enhancement of cyclic SCC crack growth rates.
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  • Toshio ENJO, Toshio KURODA, Noriyuki MITSUI
    1987 Volume 36 Issue 404 Pages 495-499
    Published: May 15, 1987
    Released: June 03, 2009
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    Hydrogen induced cracking and its fracture morphology have been studied for Ti-6Al-4V alloy with various microstructures. The susceptibility to hydrogen induced cracking and the crack propagation rate in air for delayed cracking were high for the mill annealed and β annealed specimens consisting of α+β microstructure. But the susceptibility and the propagation rate were low for the β quenched specimen consisting of α prime phase.
    The characteristic fracture morphology of hydrogen induced cracking was terrace and wall type fracture, and it was related to the hydride precipitation behavior for any microstructure. The characteristic fracture morphology of delayed cracking was observed for the β annealed specimen consisting of packets of α phase, and it was fluted fracture showing tubular voids. The mechanism of formation of the morphology was discussed.
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  • Yoneo KIKUTA, Takao ARAKI, Akio HIROSE
    1987 Volume 36 Issue 404 Pages 500-505
    Published: May 15, 1987
    Released: June 03, 2009
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    The present work deals with the effects of nonmetallic inclusions on hydrogen assisted cracking (HAC) and its fracture morphology. Three point bending test was carried out, using hydrogen charged and uncharged specimens whose sulphur contents were changed in the range 10 to 510ppm. The hydrogen diffusion coefficients of these steels were measured to investigate the hydorgen trapping effect of inclusions. The follownig results were obtained in this work.
    The critical stress intensity (Kc) values for the hydrogen uncharged specimens decreased with increasing inclusions. Therefore, inclusions had a detrimental effect on ductile facture of steels. In this test, deep voids induced by MnS inclusions were observed on the fracture surfaces of the specimens with higher sulphur contents. For the hydrogenated specimens, the threshold stress intensity (KTH) values increased but the crack propagation rates decreased with increasing inclusions. Therefore, it was concluded that inclusions suppressed both the initiation and propagation of HAC. Though the dominant fracture mode was quasi-cleavage in this test, secondary cracks induced by MnS inclusions were observed on the fracture surfaces of high sulphur steels at high K values. However, such secondary cracks diminished with decreasing K levels. At KTH levels, all of the steels exhibited the same fracture appearances independent of sulphur contents. The above mentioned effects of inclusions on HAC were due to the reduction of hydrogen concentration at the crack tip and the delay of hydrogen diffusion to the crack tip, which were caused by the hydrogen trapping of sulphides.
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  • Seiji FUKUYAMA, Kiyoshi YOKOGAWA, Michio ARAKI
    1987 Volume 36 Issue 404 Pages 506-512
    Published: May 15, 1987
    Released: June 03, 2009
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    The elastic-plastic fracture toughness and fatigue crack growth properties of the soluted and the sensitized SUS 304 stainless steel were investigated in high pressure hydrogen at room temperature.
    The results obtained are as follows;
    (1) J1H value of the sensitized SUS 304 was smaller than that of the soluted one and both of them decreased with increasing hydrogen pressure.
    (2) On the fracture surface of the sensitized SUS 304 fractured in hydrogen, the brittle and transgranular fracture as well as the intergranular fracture were observed, but no streched zone was observed. For the soluted one, only the brittle and transgranular fracture was observed.
    (3) The fatigue crack growth rate of SUS 304 in hydrogen was larger than that in argon for both the soluted and sensitized ones. The hydrogen susceptibility of the sensitized SUS 304 was larger than that of the soluted one.
    (4) The brittle and transgranular fracture was mainly observed on the soluted SUS 304 and the intergranular fracture was observed on the sensitized one in the fatigue tests under high hydrogen pressures.
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  • Ryuichiro EBARA, Yoshikazu YAMADA, Tamotsu YAMADA, Katsuaki KUBOTA
    1987 Volume 36 Issue 404 Pages 513-519
    Published: May 15, 1987
    Released: June 03, 2009
    JOURNALS FREE ACCESS
    In order to investigate the high temperature fracture behavior of hot forging die steel, low cycle fatigue life and crack propagation tests of SKD62 were carried out. The effects of testing temperature, hardness of base metal and surface hardening treatments such as ion nitriding, tuftriding and sul-surf treatment on low cycle fatigue strength and crack propagation rate were investigated.
    Decrease of low cycle fatigue strength and increase of crack propagation rate were comparatively prominent at 450°C. Increase of hardness of base metal was most effective to improve the low cycle fatigue strength of SKD62 due to delay of crack initiation. Among various surface treatments, ion nitriding was most effective to improve the low cycle fatigue strength of SKD62.
    Striation was predominant in the fracture surfaces of all low cycle fatigue tested specimens in this experiments.
    Thermal fatigue crack initiation and propagation tests were also conducted by heating specimens up to 1000°C by use of a laboratory made thermal fatigue testing machine. By lowering the temperature difference between heating and cooling, crack initiation life was increased and crack propagation rate was decelerated. Striation like pattern appeared remarkably on the thermal fatigue fracture surface. The same type of fracture surface was observed on the thermal fatigue failed fracture surface of hot forging die.
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  • N. Yamazaki
    1987 Volume 36 Issue 404 Pages 520-526
    Published: May 15, 1987
    Released: June 03, 2009
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