材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
38 巻 , 428 号
選択された号の論文の17件中1~17を表示しています
  • 冨田 恵之
    1989 年 38 巻 428 号 p. 466-471
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Structural low alloy steels, S45C and SNCM 439, have been studied to determine the effect of the shape of sulfide inclusions on improvement in the mechanical properties of quenched and highly tempered structural low alloy steels. The shape of sulfide inclusions was changed by varying the ratio of the hot-rolling reduction. Tensile and Charpy U-notch (CUN) impact tests were performed on the specimens with different testing orientations. Morphology of the sulfide inclusions was examined by an electron probe microanalizer and optical microscopy. Fractography was carried out by scanning electron microscopy. Modifing the shape of MnS inclusions from the stringer to the ellipse by decreasing hot-rolling reduction from 98 to 80% significantly increased room temperature fracture ductility in the transverse testing orientation independent of the steels. This also significantly improved the room temperature CUN impact energy in transverse testing orientation of the steels independent of notch orientation. However, the mechanical isotropy achieved by modifying the inclusions declined as test temperature decreased. Fractography revealed that the mechanical properties were improved when fracture occurred by ductile mode with MnS-void nucleation and growth, followed by localized shear between the inclusion-nucleated voids. The beneficial effect on the mechanical isotropy is discussed in terms of the model involving the formation of voids at inclusion sites and their growth and eventual coalescene by local shear during plastic deformation.
  • 圓城 敏男, 黒田 敏雄, 今西 龍介
    1989 年 38 巻 428 号 p. 472-477
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    The relation between microstructure and toughness in the weld heat affected zone of SUS329J1 duplex stainless steel has been investigated by means of fractography. The base metal of SUS329J1 had duplex microstructure consisting of α phase and elongated γ phase.
    The upper shelf energy in the Charpy impact value versus temperature curve was affected by the location of V notch of Charpy impact specimen. For the specimen in which crack propagation occurred in the short transverse direction, the energy was highest, because of the presence of the platelet and elongated γ phase. The presence of γ phase increased remarkably the toughness for the ductile fracture, but hardly affected the brittle fracture.
    As for the microstructure of weld heat affected zone, the specimen heated up to 1373K had the α+γ duplex microstructure and was similar to that of the base metal. The Charpy impact value was also similar to that of the base metal.
    For the specimen heated at 1473K and 1573K such as the condition of weld bond region, the toughness considerably decreased, because of the large grain size, the decrease of the volume fraction of γ phase and the precipitation of Cr2N in the α phase.
  • 荒木 孝雄, 廣瀬 明夫, 内原 正人, 河野 渉, 本多 啓三, 近藤 光昇
    1989 年 38 巻 428 号 p. 478-483
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Mechanical properties and fracture behaviour of Ti-50.7at%Ni shape memory alloy and its laser weld joint have been investigated.
    The base metal aged at 673K for 3.6ks exhibited super elasticity and higher tensile strength than the solution base metal. However, the aged material showed less fracture strain and more brittle fracture surface than the solution material.
    Butt welding of 3mm thick Ti-Ni alloy was performed using 10kW CO2 laser. The laser welded specimens showed a successful shape memory effect and super elasticity. These properties were identical with those of the base metal.
    However, the tensile strength and the fracture strain of the laser welded specimen were less than those of the base metal. The fracture occurred at the columar crystal boundary at the center of the weld metal. The boundary was perpendicular to the direction of the loading and, moreover, oxide inclusions crystallized at the boundary. These facts seem to cause low strength of the weld joint.
    The fracture strain of the welded specimen, nevertheless, was more than 6% which is the maximum recoverable elongation in polycrystal Ti-Ni base metal. Laser weld is, therefore, applicable to the joining of Ti-Ni shape memory alloy when the alloy is used as a functional material.
  • 片桐 一宗, 斎藤 幸司, 大上 真志, 岡田 東一, 永田 明彦, 能登 宏七, 渡辺 和雄
    1989 年 38 巻 428 号 p. 484-489
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    An investigation was made on the strain dependence of critical cuurent Ic for three kinds of practical Nb3Sn superconducting wires which are in the course of development, with an emphasis on the correlation with wire constitution.
    In the internal tin diffusion processed wires with a single tin core at the center, the reversible strain limit, εirrev was small and the strain sensitivity of Ic was high. This is ascribed to the strain concentration induced by Kirkendall voids observed in the center of fracture surface.
    Internal reinforcement using SUS 405 steel increased both εm, the strain corresponding to peak Ic, and the strain sensitivity, and decreased the εirrev in addition to a marked increase of flow stress. In the light of both the serration in the stress-strain relation and fracture surface morphology, the degradation of strain characteristics are attributable to the strain concentration in Nb3Sn layer associated with localized deformation of the steel at low temperatures.
    In the external tin diffusion in situ processed wires, both Nb3Sn layer formed in the periphery and the unreacted core in the center of the wire controlled the strain characteristics. The smaller the core size was, the larger the critical current density and the smaller the εm or εirrev. Inhomogeneity of tin diffusion in the cross section as well as in the longitudinal direction resulted in deviation of the core and tin balling, respectively. They deteriorated the strain characteristics of the wire significantly.
    Improvements of the strain characteristics in these wires through proper constitution and heat treatment were briefly discussed.
  • 浅見 克敏, 新開 毅, 田中 俊一郎
    1989 年 38 巻 428 号 p. 490-495
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Tensile tests of Si3N4/S45C bonding bar-type specimens, which were jointed by metallizing method, were carried out in laboratory air at room temperature. Then, the relation between the fracture stress and the appearance of fracture surface was investigated in detail.
    Generally, the crack initiation site was at the bonding part, and the crack propagated into the ceramic. In this case, the following relation was observed between the fracture stress, σf (MPa) and the square root of the mist area, √Ah(mm).
    σf=540(√Ah)-0.47
    Furthermore, the size effect was recognized on the fracture stress and the following equation was deduced for the fracture stress, σf (MPa) based on fracture mechanics and fractography.
    σf=25.8/√d
    where d(m) is the diameter of specimen.
    When the diameter of specimen increased, the crack initiated in the ceramic in some of the specimens. In this case, the fracture stress was low. The reason was considered that the bonding-induced residual tensile stress increased with increasing the diameter of specimen and/or the value of residual stress was remarkably different at each specimen.
  • 中村 春夫, 小林 英男, 荒居 善雄
    1989 年 38 巻 428 号 p. 496-500
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    By utilizing fractographic approach, an applicability of a chevron notched specimen as well as a conventional compact specimen to plain strain fracture toughness, KIC, tests was examined for brittle materials; a ceramics (Si3N4), a high strength graphite (IG-11), an alumina particulate filled epoxide composite, and a low alloy steel (A533B-1) at lower shelf and transition temperature regions. The KIC test method using chevron notched specimens was found useful for these materials except A533B-1. The cleavage fracture toughness values for A533B-1 were overestimated due to difficulty of introducing a precrack by cleavage from the chevron notch tip.
    Further fractographic examination showed that in both IG-11 and the epoxide composite, micro scopic appearances of a fracture toughness, a fatigue, and a stress corrosion cracking specimens were almost the same, suggesting the similar crack growing mechanism in these cases.
  • 西谷 弘信, 鹿毛 正治, 薬師寺 輝敏
    1989 年 38 巻 428 号 p. 501-506
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Rotating bending fatigue tests and pulsating tensile fatigue tests were carried out using the notched and CT specimens cut out in various directions from a rolled steel. The material used had discoid inclusions with a remarkable directionality, in spite of its slightly laminated structures. The crack growth rate in each directional specimen was measured by an optical microscope and the fracture surfaces were observed by a scanning electron microscope. The main results obtained are as follows. (1) As for the anisotropy in the crack initiation process and in the process of initial crack propagation, the effect of discoid inclusions was large, as in the case of the anisotropy of the fatigue limit. This is because in the direction where the inclusions give effect, the cracks propagate immediately from the discoid inclusions, while in the direction where the inclusions give no effect, many repetitions are needed until the cracks initiate. (2) As for the anisotropy of the propagating process of large cracks, the crack growth rate was largest in the case of specimens whose cracks propagate along the inclusions, but the anisotropy of the crack propagation was small in comparison with that of the fatigue limit. This is because the fatigue limit is determined by the limiting condition for the propagation of cracks initiated from inclusions, while the crack growth rate is determined by the average properties of the crack front.
  • 杉山 好弘, 浅見 克敏, 黒岩 秀樹
    1989 年 38 巻 428 号 p. 507-513
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    The fatigue crack propagation characteristics at the stage 2 in spheroidal graphite cast irons, whose matrix-structures were changed by heat treatments in order to improve the static strength, have been compared with those of the as-cast materials. Fatigue tests were carried out at stress ratio, R=0.1, and the results were investigated from the viewpoints of the crack closure and the fractography.
    In the case that the matrix-structure was changed into the single-phase of bainite by austempering, the static strength increased, while the fatigue crack propagation resistance decreased in low ΔK region. On the other hand, in the case that the matrix-structure was changed into the dual-phase of ferrite and martensite by quenching from the (α+γ) phase region, both the static strength and the fatigue crack propagation resistance increased. The difference in fatigue crack propagation resistance between the two heat-treated materials was explained from the crack closure behavior.
  • 大塚 昭夫, 東郷 敬一郎, 吉田 誠
    1989 年 38 巻 428 号 p. 514-519
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    A fractographic study has been carried out on fatigue crack growth from a semi-elliptical surface crack under shear loading. The fatigue tests of rectangular bar specimens with a semi-elliptical surface crack were made on an aluminum alloy 2017-T4 and a weldable structural steel SM41A, using the four-point-shear loading method. SM41A showed the tensile mode growth with complicated three -dimensional crack growth surfaces, and 2017-T4 showed the shear mode growth which occurred, forming flat crack growth surfaces, in the same plane as the pre-crack. The macroscopic shapes of these crack surfaces formed by the tensile mode growth and by the shear mode growth have shown good agreement with those predicted by σmax criterion and by τmax criterion, respectively. The microscopic features of these fatigue crack growth surfaces were observed by using SEM. The tensile mode crack growth surfaces of SM41A were covered with striation pattern. The factory-roof-like surface, which was formed at the crack front under mode III-predominant deformation, was found to consist mainly of striation-like pattern. The shear mode crack growth surfaces of 2017-T4 showed rather smooth and flat feature with some steps and streaks. The direction of these streaks was found to be in accordance with the direction of the maximum shear stress at the crack front.
  • 藤田 和孝, 小寺沢 良一
    1989 年 38 巻 428 号 p. 520-526
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Microscopic fatigue crack propagation studies were carried out under periodic overstressing with different number of overstress cycles n2 using normalized 0.15% C and quenched and tempered 0.45% C steels. With decreasing n2, the acceleration of crack propagation became higher and for cracks longer than 50μm the lower limit of the understress that caused the acceleration decreased considerably. When n2 was very small (2 cycles), the acceleration in 0.15% C steel was higher than that in 0.45% C steel in agreement with the previous results on macroscopic cracks in which the acceleration was higher in materials of lower strength. Microscopic fracture surfaces in short cracks (less than 200μm) consisted of small facets which were supposed to be related to crystal structures and were mostly tilted with respect to the direction perpendicular to the tensile axis. Cracks observed on specimen surfaces sometimes stopped at grain boundaries and propagated intermittently. These observations suggest that microstructure (grain boundary and crystallographic orientation) has a significant effect on propagation of short cracks. As for long cracks, microscopic fracture surfaces consisted of large facets which were mostly perpendicular to the tensile axis and cracks propagated steadily, indicating that microstructure has less effect. Hill-to-valley matching of striation-like patterns was observed on pairs of fracture surfaces under overstressing, indicating that the cracks propagated in zigzag manner. Under steady stressing, matching of striation-like patterns was not observed. These suggest that the acceleration under overstressing is related to the zigzag crack propagation.
  • 橘内 良雄, 吉久 悦二
    1989 年 38 巻 428 号 p. 527-532
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Fatigue crack growth tests in butt-welded joints of HT80 and STS42 steels were carried out using compact type (CT), center-cracked tension (CCT) and single edge-cracked tension (SECT) specimens at room temperature and 173K, and their fracture surfaces were examined using a scanning and a transmission electron microscopes to evaluate the influence of residual stress on the formation of fracture morphologies.
    As the fatigue crack propagated through compressive residual stress fields, the fracture surface was covered with a thin oxide film which was produced by mutual contact of crack surfaces. At ΔK above 20MPa√m or the crack growth rate above 2×10-8m/cycle, the fracture morphologies in the base metal and welded joints were dominated by striations independent of the test temperature. At the low ΔK region or the crack growth rate below 1×10-9m/cycle, fracture morphologies showed that the fatigue crack propagated along the microstructures with favourite orientation to the crack growth. The intergranular like facets were formed in the weld metal of HT80 steel at ΔK ranging from 4 to 12MPa√m. The maximum area percentage of the intergranular like facets, however, was considerably lower than that of intergranular facets formed in the base metal. The striation spacings in the welded joints were correlated well with the effective stress intensity factor range, ΔKeff R, which was estimated by superposition of the respective stress intensity factors for the residual stress fields and for the applied stresses.
  • 浦島 親行, 西田 新一
    1989 年 38 巻 428 号 p. 533-538
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Segregation is inevitably recognized in structural steels and seemed to be very harmful for thier reliability. Then, some fatigue tests have been performed to investigate the harmfulness of segregation. The main results obtained are as follows;
    (1) Carbon, manganese and phosphorous were segregated positively in the segregation band, where the proof stress, tensile strength and hardness became higher but the elongation and reduction of area became lower than the other positions.
    (2) The rotating bending fatigue strength varied little irrespective of the presence or absence of segregation, the degree of segregation or the orientation of test specimens in the rail.
    (3) The fatigue crack initiated in the position where there is no segregation, and its originating place showed the flat surface which is seemed to be a parallel face along a pearlite lamellar.
    (4) The axial pulsating fatigue strength of bolt-holed specimens varied little with the presence or absence of segregation and degree of segragation.
    (5) It is considered that the reason why the segregation has no influence on the fatigue strength is due to the high resistance for slip in the segregation band.
  • 福山 誠司, 横川 清志, 荒木 道郎, 小鑓 幸雄, 青木 宏, 山田 良雄
    1989 年 38 巻 428 号 p. 539-545
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    The fatigue crack growth properties of the Inconel 718 and Udimet 720 Ni-base alloys being used for liquid hydrogen fueled rocket engine materials were investigated as functions of ΔK and frequency in a high pressure hydrogen of 19.7MPa at room temperature. The results obtained are as follows;
    (1) The fatigue crack growth rate in hydrogen was larger than that in argon for both Inconel 718 and Udimet 720. The effect of hydrogen on fatigue crack growth rate increased with decreasing the frequency of the cyclic loading. The effect of hydrogen on fatigue crack growth of Udimet 720 was higher than that of Inconel 718.
    (2) Above the ΔK which the striations were observed on the fracture surface in argon, hydrogen showed marked effect on the fatigue crack growth, i.e., the fracture along the interfaces between δ phase and γ matrix for Inconel 718 and that the interfaces between γ' phase and γ matrix for Udimet 720 were observed on the fracture surface in hydrogen, respectively.
  • 向井 喜彦, 村田 雅人, 王 静波
    1989 年 38 巻 428 号 p. 546-551
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    Hydrogen embrittlement type stress corrosion cracking of duplex stainless steel and its welded joint in acid environment has been studied. It was found that the electrode potential and ferrite content affected the susceptibility of duplex stainless steel to HESCC. At a less noble potential the time to failure decreased, while it increased at the noble side. Also, it was found that the crack growth rate decreased significantly with decreasing ferrite content. When the ferrite content was less than 40%, cracks did not propagate. The observation of the fracture surface showed the cleavage type fracture in α phase and the ductile fracture in γ phase. This means that γ phase would block the cracks propagating through α phase. According to the analysis of hydrogen diffusion, it was shown that the concentrations of hydrostatic stress and hydrogen appeared in α phase near the tip of γ phase, and this position became the most probable crack initiation site for HESCC.
  • 内田 仁, 井上 尚三, 小山 雅隆, 小寺澤 啓司
    1989 年 38 巻 428 号 p. 552-556
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    The Crystallography of transgranular stress corrosion cracking (SCC) in pure copper single crystals was studied by scanning electron microscopy. The regular prismatic specimens oriented for [001], [101], [111], [112], [213] and 0.50 in Schmid factor were prepared, and they were SCC-tested in 1kmol·m-3 NaNO2 solution at room temperature by slow strain rate technique. The fractographic results showed that many cracks nucleated from the specimen surfaces with frequent slip-steps, producing a black turnish film. The susceptibility to SCC estimated from the nominal stress-strain curves increased markedly in the [101]- and [111]-oriented specimens. Most of the fracture surfaces showed the characteristic of river-like pattern, which was formed by the crack growth along ‹110› direction on {110} plane. The appearance of {111}-‹112› type was also observed partly in the initial stage of crack growth. It was found that the crack growth of {110}-‹110› type was strongly controlled by the normal stress to {110} plane which takes the smallest angle with respect to tensile axis.
  • 種池 昌彦, 村上 理一, 秋園 幸一
    1989 年 38 巻 428 号 p. 557-561
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
    The corrosion fatigue crack growth behavior in the butt welded joint of high tensile strength steel has been studied in a synthetic sea water and discussed in relation to the welding residual stress and corrosion deposits.
    For the base metal, the effect of synthetic sea water on da/dN depended on the stress ratio. At a high stress ratio, a little acceleration of da/dN by the synthetic sea water was observed while at a low stress ratio the da/dN tended to be lower than that in air. For the welded joint, the da/dN was affected by a compressive residual stress in both synthetic sea water and air, and was greater in air than in synthetic sea water. Such a crack growth behavior is related to the crack opening and closure behavior which is influenced by the corrosion deposits and the compressive residual stress.
  • 福田 武人
    1989 年 38 巻 428 号 p. 562-567
    発行日: 1989/05/15
    公開日: 2009/06/03
    ジャーナル フリー
feedback
Top