材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
54 巻 , 2 号
選択された号の論文の19件中1~19を表示しています
特集 高温強度
巻頭言
論文
  • 永江 勇二, 青砥 紀身
    2005 年 54 巻 2 号 p. 116-121
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    It has been found that magnetic property changes in austenitic stainless steel subjected to creep at high temperature. The change of magnetic property is mainly due to decrease the chromium concentration in the vicinity of grain boundary and transform into martensite in the area. But this result is for short-term creep. It is necessary to evaluate the long-term creep in order to develop non-destructive technique for plants. Moreover it is important to evaluate the fatigue. The change of magnetic property for those damages at high temperatures is investigated. The transformation into martensite is observed for both the long-term creep and fatigue. The magnetic regions are observed in sever deformed area and near crack. Then the formation of magnetic phases is related to the damage.
  • 阪口 基己, 岡崎 正和
    2005 年 54 巻 2 号 p. 122-129
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    A cellular microstructure may be nucleated in single crystal Ni-based superalloys when they have experienced a local damage associated with a plastic deformation during their in-service and post-service periods of gas turbine. In this work, an analytical method to investigate the morphological evolution in the cellular microstructure is proposed. The method is essentially based on the Eshelby's micromechanics theory, and it has been extended so as to be applied for material system containing high volume fraction inclusions, by employing the average stress field approximation by Mori and Tanaka. This method enables us to estimate a stable shape of precipitate in the material system, which must be influenced by many factors : e.g. precipitate volume fraction ; Young's modulus ratio and lattice misfit between matrix and precipitate ; external stress field in multi-axial state ; and heterogeneity of plastic strain between matrix and precipitate. A series of numerical calculations were summarized on the stable shape maps. The application of the method to predict the γ' rafting in superalloys during creep showed that the proposed method supplied reasonable explanations to all the experimental observations, and that the heterogeneity of plastic strain between matrix and precipitates may play a significant role in the shape stability of the precipitate. Furthermore, the method could successfully estimate the morphology in the cellular microstructure formed around the spherical indentation in CMSX-4 single crystal Ni-based superalloy. The present method will be a useful tool for failure analysis of superalloy components and for an estimation of in-service stress state.
  • 山本 真人, 新田 明人, 北村 隆行
    2005 年 54 巻 2 号 p. 130-135
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    In order to clarify the crack propagation property of Nickel-based directionally solidified superalloy, longitudinal loading (L-type) specimens and transverse loading (T-type) specimens were subjected to the high temperature fatigue crack propagation tests. Fatigue crack propagation rate was correlated fairly well with effective stress intensity factor range ΔKeff, regardless of specimen type (L or T), stress range, and R ratio. In detail, crack propagation rate in T specimen showed eminent fluctuation and it was partially accelerated to 3 to 5 times faster than the average. Detailed observation of specimens revealed that the fluctuation was strongly dependent on the micro-structure along the crack propagation path. Both of transgranular and intergranular crack types were observed on the crack propagation path of T specimen, while that in L specimen showed only the transgranular type. Moreover, transgranular crack showed two different failure planes, they were along {111} or {001} planes, respectively. Since most part of the whole tests were governed by transgranular cracking, they showed mostly the same propagation property. Intergranular crack in T specimen showed much faster propagation than the transgranular crack, and caused eminent fluctuation of propagation rate.
  • 筧 幸次, 高橋 智
    2005 年 54 巻 2 号 p. 136-142
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    In single crystals of Ni-based superalloys, the γ' precipitate size has been shown to affect both the tensile strength and the creep behavior at intermediate temperatures. The microstructure of Ni-based superalloys contains primary cuboidal γ' particles that precipitate during aging treatment, and cooling γ' particles that precipitate during cooling from the aging temperature. In the Ni-based superalloy containing a high volume fraction of γ' precipitates, the change in the morphology of the secondary γ' precipitates in a matrix channel has been found to affect the creep strength. In this study, three kinds of aged specimens were prepared to investigate the influence of the morphology of γ' precipitates on the strengths of CMSX4 alloy. Slow furnace cooling from the aging temperature was employed to obtain a clean matrix channel completely devoid of secondary γ' precipitates. In order to clarify the effect of secondary γ' precipitates, the strengths of the furnace-cooled specimens were compared with those of the forced-airquenched specimens containing numerous superfine γ' precipitates in the matrix channel, and those of the standard two-step-aged specimens. The purpose of the present investigation is to gain a better understanding of the effect of precipitation heat treatment on the material strengths at an intermediate temperature, where the secondary γ' precipitates remain undissolved during creep deformation.
  • 時吉 巧, 猪狩 敏秀, 金谷 章宏, 紀 博徳
    2005 年 54 巻 2 号 p. 143-148
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    Quantitative prediction of crack growth under displacement-controlled conditions such as thermal fatigue is a key to the residual life prediction of plant components. In a previous paper, the authors proposed a simplified prediction method of fracture mechanics parameters such as J and C* of a perforated plate under thermal fatigue, on the basis of the reference stress approach under displacement-controlled conditions. In this paper, the fracture mechanics parameters of a CCT specimen and structural models of CrMoV cast steel under displacement-controlled conditions were experimentally and numerically examined on the basis of the proposed method. The ratio of the inelastic and the elastic crack opening displacement, as well as the ratio of the inelastic and the elastic load point displacement, was used to correlate the fracture mechanics parameters in the inelastic and elastic regions. The proposed method based on displacements was found to be insensitive to a small variation in the predicted macroscopic load in comparison with the original reference stress method, and is considered to be applicable to displacement-controlled conditions such as thermal fatigue.
  • 藤本 正義, 坂根 政男, 伊達 新吾, 吉田 博明
    2005 年 54 巻 2 号 p. 149-154
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    This paper studies the effect of stress biaxiality on creep rupture time and void growth for 2.25Cr-1Mo steel at 823K. Biaxial tension creep tests were carried out using 2.25Cr-1Mo cruciform specimens, and rupture times under biaxial stress states were experimentally obtained. Void growth in biaxial creep stages was observed by intermitting creep testing. The biaxial creep rupture times were slightly longer than the uniaxial creep rupture times in the correlation with Mises equivalent stress. Void nucleated earlier in biaxial stress states than in uniaxial stress states. Void number density and A-parameter were detected in the rupture life ratio less than 0.5 in biaxial stress states, whereas those were not detected before the life ratio of 0.7 in uniaxial stress state. The relationship between the void nucleation and rupture time in biaxial stress states was discussed based on the fracture mode.
  • 本郷 宏通, 山崎 政義, 渡部 隆, 田淵 正明, 田辺 龍彦, 門馬 義雄
    2005 年 54 巻 2 号 p. 155-161
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    Evaluation of creep properties of the welded joint through taking local fluctuation of the properties into consideration is experimentally or analytically seldom carried out. In this context, the purposes of the present study are to examine the surface strain distribution in the weld metal of a full thickness welded joint specimen and subsequently to investigate the local variation in the properties of the all-weld metal part of the joint using miniature specimens. A welded joint was prepared for 316FR steel plates by gas tungsten arc welding process using Mod. 316 filler wire. Creep tests were conducted at 823K in air using full thickness large welded joint specimens, HAZ and all-weld metal miniature specimens. By interrupting the creep test for the full thickness welded joint specimen, we observed the change in the uniaxial creep strain distribution in the weld metal in the thickness direction of the plate. The last layer of weld metal showed considerably larger creep strain than the central layers of the weld metal. The elastic-plastic creep analysis of the welded joint specimen by FEM was performed using these data. Finite element simulation performed for full-thickness welded joints provided creep strain distribution that is consistent with measured values. From the results above, it is concluded that the creep properties of weld metal in multi-pass, multi-layer welded joints strongly depend on the location of specimen sampling. It is necessary to take the fluctuation of material properties of a weld metal part into consideration when we perform simulation of creep deformation of a welded joint with sufficient accuracy.
  • 田淵 正明, 近藤 雅之, 本郷 宏通, 渡部 隆, 殷 福星, 阿部 冨士雄
    2005 年 54 巻 2 号 p. 162-167
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type IV fracture, which occurs as a result of the formation and growth of creep voids and cracks on grain boundaries in the fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr-3W-3Co-VNb steels with boron content varying from 47 to 180ppm and with nitrogen as low as 20ppm were prepared. The steel plates were welded by gas tungsten arc welding and creep tested at 923K. It was found that the fine-grained HAZ did not exist in the present steel weldments ; that was quite different from the conventional high Cr steels such as P91 and P92 steel. Boron addition had the effect to suppress coarsening of grain boundary carbides during creep not only in base metal but also in HAZ. As a result of these phenomena, the welded joints of present steels showed no Type IV fractures and much better creep lives than those of the conventional high Cr steel weldments.
  • 高橋 由紀夫, 屋口 正次
    2005 年 54 巻 2 号 p. 168-173
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    Prediction of failure life under creep-fatigue condition is of practical importance for sound design and operation of high-temperature plants. Stress-based time-fraction approach often overpredicts failure life because of difference of deformation under monotonic creep and creep-fatigue loading. Strain-based life prediction procedure called ductility exhaustion method has been developed to overcome shortcoming of simpler stress-based approach. However, overly conservative prediction is obtained for some materials by the conventional way of creep damage counting in the ductility exhaustion method. A new method which includes alternative ways of creep damage calculation and modeling creep-fatigue interaction, was developed in this study. This method was applied to a number of creep-fatigue tests conducted for modified 9Cr-1Mo steel (P91) and HCM12A (P122). Excellent agreement was obtained between predicted and experimental lives.
  • 時政 勝行, 高畑 智
    2005 年 54 巻 2 号 p. 174-180
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    A genetic algorithm (GA) is a mathematical search technique based on the principle of natural selection and genetic combination, and there are many problems in the research fields of the mechanical behavior of materials to which a GA can be applied. The present paper investigates the improvement of creep-fatigue damage rule for Mod.9Cr-1Mo steel by using the GA program, which was developed by the authors in order to estimate the values of material parameters required to describe the creep-fatigue damage growth models of materials. Three kinds of creep-fatigue damage growth models were studied, such as a model proposed for Mod.9Cr-1Mo steel, a model proposed for 316LC steel and a more general model proposed in the present study. Optimization of material parameters in each model by GA analysis was conducted based on the results of constant-strain amplitude creep-fatigue tests and two-step variable-strain waveform creep-fatigue tests. As the results, it is found that the 316LC type creep-fatigue damage growth model can predict more precisely creep-fatigue crack growth behaviors and remaining life of Mod.9Cr-1Mo steel than the other two models.
  • 伊藤 隆基, 服部 修次, 藤井 弘志, 若月 勇人, 渡士 克己, 橋本 貴司
    2005 年 54 巻 2 号 p. 181-186
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    An ultrasonic fatigue testing machine was developed to obtain the very high cycle fatigue life at elevated temperature for safety and reliability of structural components in the faster breeder reactor (FBR). This testing machine consists of an amplifier, booster, horn and equipments such as a system controller and data acquisition. The test specimen is attached at the end of the horn. The electric power generated in the amplifier is transformed into the mechanical vibration in the converter and is magnified in the booster and horn. The developed ultrasonic fatigue testing machine enables to carry out the fatigue test at 20kHz so that it can perform the very high cycle fatigue test within a very shorter time as compared with the regular fatigue testing machines such as a hydraulic fatigue testing machine. This study carried out very high cycle fatigue tests using type STBA 24, the steel for tube in boiler and heat exchanger, at room and elevated (673K) temperatures by the developed testing and conventional hydraulic testing machines, and obtained the fatigue lives. This paper also described the cracks observed on specimen surface of fatigued specimen and discussed the very high cycle fatigue strength properties. It was confirmed that the fatigue data obtained by the ultrasonic fatigue testing machine are continuous and compatible with the results obtained by the hydraulic tension-compression testing machine. Fatigue lives more than 106cycles at room and high temperatures can be predicted conservatively by the best fit design curve employed in the nuclear power plant design.
  • 山崎 泰広, 岡崎 正和, 平野 一美
    2005 年 54 巻 2 号 p. 187-192
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    The isothermal low cycle fatigue (LCF) fracture behavior of a new generation titanium alloy matrix composite, SP-700/SCS-6, were investigated compared with the monolithic matrix alloy. To study the effects of the test temperature and the loading frequency on the LCF fracture behavior in SP-700/SCS-6, the LCF tests were performed under strain-controlled condition at room temperature and 450°C. In the LCF tests two strain wave shapes were applied : the fast-fast wave in which the loading frequency was 0.5 Hz, and the slow-slow wave in which it was 1/360 Hz, respectively. The conclusions obtained from the experimental results are summarized as follows : (1) The LCF lives of the composite were almost comparable to those of the matrix alloy, on the basis of strain range. In other words, the performance of the present composite material can be absolutely improved, since the stiffness and the deformation resistance can significantly increased by the composition. (2) The fatigue cracks were initiated from the matrix part at the specimen corner. The fiber pull-out was not so significant on the fracture surface. (3) The LCF lives of the composite at 450°C were longer than those at room temperature. This trend was in contrast to the monolithic matrix alloy which exhibits a normal temperature dependence in the LCF lives. (4) The LCF lives of the composite under the slow-slow wave was noticeably shorter than those under the fast-fast wave at high temperature. This trend was familiar to the conventional monolithic materials.
  • 佐藤 知広, 齋藤 賢一, 新家 昇
    2005 年 54 巻 2 号 p. 193-200
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    An SMA (shape memory alloy) is a functional material with a unique property known as the shape memory effect, or superelasticity. Microscopically, the mechanical actuation of this effect is based on reversible transformation between different crystal phases. To clarify the atomistic mechanism in SMA, we perform molecular dynamics simulation (MDS) of phase transformations for a Ni-Ti alloy, a typical alloy used for engineering SMAs. EAM potential, which can produce both B2 and B19' structures (stable crystal phases of Ni-Ti), is adopted to model the interatomic interaction of the nickel and titanium atomic systems. Two different-sized MDS models are constructed with unit cell structures of B2 phase. These structures are surrounded by free surfaces and constrained regions so as to be subjected to uniaxial tensile loading. A series of reversible processes likely to occur in SMA, including loading, unloading, heating, and cooling, is reproduced by corresponding stages of the MDS. Phase transformation is thought to be observable by detecting the local interatomic distances and bonding angles peculiar to B19' structure (martensite). During tensile loading simulations, the martensite crystal structure is always observed, having transformed from the B2 structure. At a large strain, models exhibit a rapid propagation of local lattice distortions accompanied by the formation of martensite. In unloading simulations, the larger model contains relatively less martensite than the smaller model. The discrepancy with regards to model size may depend on a different degree of constraint strength. Reverse transformation (from B19' to B2) occurs mainly in the subsequent heating stage, in which the stress is observed to increase under constant residual strain.
  • 塙 悟史, 石原 正博, 本橋 嘉信
    2005 年 54 巻 2 号 p. 201-206
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    The brittle fracture model for multiaxial tensile stresses was proposed and its applicability was studied by comparing experimental data. The proposed model can treat microstructures such as grain size and pore size in it, and the fracture probability can be calculated as a function of multiaxial stresses σ1, σ2, and σ3. As experimental data, two types of graphite such as IG-110 and PGX were examined. From the comparison it was shown that the predicted strength agrees well with experimental data not only for the average strength but also for the strength distribution, and that predicted and experimental strengths were fit quite well to the Weibull statistical distribution. Moreover, by applying this model it was predicted that the multiaxial strength behavior would not depend on pore/grain microstructure and specimen volume.
  • 斧 督人, 石田 渉, 中尾 航, 安藤 柱, 森 俊太郎, 横内 正洋
    2005 年 54 巻 2 号 p. 207-214
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    Mullite/SiC whisker composite ceramic was sintered. The three point bending specimen was made from the composite ceramic. A semi-elliptical surface crack up to 400μm in diameter (aspect ratio ≈ 0.9) was introduced on the specimen. The basic crack-healing behavior was studied systematically as a function of crack-healing temperature, and the bending strength of the crack-healed sample was also tested systematically. Followings are main conclusions obtained ; (1) The mullite reinforced by SiC whiskers exhibited a large crack-healing ability. (2) The fracture toughness (KIC) of the mullite composite was increased about 60% by the SiC whisker reinforcement. (3) The crack-healed mullite exhibited lower bending strength (σB) than that of the crack-healed base material by 150∼200MPa. (4) The mullite was able to heal a crack even under constant or cyclic stresses. The critical stress intensity factor (KHSC) for the healing was found to be 2.1MPa · m1/2.
  • 中出 且之, 黒田 敏雄
    2005 年 54 巻 2 号 p. 215-220
    発行日: 2005年
    公開日: 2006/04/07
    ジャーナル フリー
    The influence of sigma phase on the hydrogen embrittlement in the 329J4L super duplex stainless weld metal was investigated by 3-dimensional fracture analysis. In the case of ferrite-austenite as-welded specimen, a little reduction of notch tensile strength was recognized since a little hydrogen cause the hydrogen embrittlement of ferrite. On the basis of the microstructure examination, hydrogen cracking preferentially occurred in the ferrite, while widmanstatten austenite showed ductile fracture. On the one hand, when hydrogen charging was carried out for weld metal precipitated 40% sigma phase (sigma phase-austenite microstructure), the notch tensile strength drastically dropped compared to hydrogenated as-welded specimen. This strength loss had a dependency of the amount of sigma phase. The susceptibility to hydrogen embrittlement of sigma phase was very high and it was clearly found that sigma phase strongly enhanced hydrogen embrittlement.
    The fracture surface was corresponded to typical widmanstatten microstructure. The area of sigma phase was always lower than other ductile area on the 3-dimensional fracture surface since sigma phase strongly promoted hydrogen embrittlement. From the viewpoint of microstructure, the ferrite almost decomposed and 40% sigma phase was present. Consequently, it could be concluded that sigma phase itself and sigma/widmanstatten austenite phase boundaries were preferential hydrogen cracking sites in the 329J4L weld metal.
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