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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 64 (1978), No. 7

  • 「鉄鋼材料の破壊靱性」特集号刊行に寄せて

    pp. 829-830

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  • Study of Drop Weight Test Procedure for Evaluation of Fracture Toughness of Steels

    pp. 831-840

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    A study of the drop weight test procedure for the evaluation of fracture toughness of steels has been made using normal P-2 type specimen and fatigue notch type specimen. NDTTs of the steel having high susceptibility to temper embrittlement, which are evaluated by using P-2 type specimen, are significantly affected by the heat affected zone under the crack starter bear. In this case, the drop weight test of the fatigue notch type specimen is recommended.
    There are some steels showing the large deviation of NDTT from the relation between NDTT and FATT which are widely known. For these steels, a method to estimate the deviation has been proposed.
    It has been also found that NDTT has a good relationship to shear fracture transition property of the steels obtained by the fatigue crack notch Charpy impact test.
  • Fracture Toughness of Temper-Embrittled Medium Carbon Steels

    pp. 841-850

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    In order to find a clue to establish the relationship between fracture toughness and metallurgical factors, macroscopic energy (GIC) for intergranular fracture of temper embrittled 0.3%C-1%Mn-1%Cr-0.02%P-0-3%Ni steels was investigated and it was compared with the surface energy of a crack (γ: true surface energy, γp: plastic strain energy in front of a crack) introduced from Griffith-Orowan's thermodynamic and/or microscopic criterion. To obtain the exact fracture toughness (GIC) corresponding to intergranular fracture due to temper embrittlement, it is required not only to exclude the influence of stretched zone formation or normal rupture in front of fatigue pre-crack, but also to consider the influence of pre-crack path on fracture toughness. Fractographic studies were carried out in detail with a scanning electron microscope to find the exact energy for intergranular fracture mentioned above.
    It was found that fracture toughness (GIC) corresponding to intergranular fracture due to temper embrittlement was in the order of 103 J. m-2. GIC was much bigger than γS (surface energy) and γB (grain boundary energy), and it was found to be close to γP. If it is assumed that GIC corresponds to γP, the reasons for the increase of degree of embrittlement (ΔFATT) and the decrease of GIC with Ni content in embrittled steels (P content is constant) are considered as follows. Intergranular fracture due to temper embrittlement is mainly caused by the decrease of γP, and the decrease of γP is considered, from AES analysis, to be due to the segregation of impurity elements and to the segregation of alloying elements such as Ni and Mn to austenite grain boundaries.
  • Relation between Fracture Behavior of Ferritic Pearlitic Steels and Acoustic Emission

    pp. 851-859

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    Four kinds of ferrite-pearlite steels (JIS S10C, S20C, S40C and S55C steel) have been fractured by static tension in the temperature range from 77K to 300K.
    The evaluation of fracture behavior has been made by fracture toughness KC. critical crack opening displacement (COD) ΦC, electron fractographic and metallographic observations. They have had good correlation with acoustic emission (AE) characteristics such as total count, root mean square (RMS) volt and waveforms. The load for calculating fracture toughness was determined from the condition of AE where the count rate was close to zero and the occurence of large RMS volt was ceased. KC and ΦC values were monotonically decreased with the lowering of testing temperatures; the values in S10C steels were the highest, followed by those of S40C steels, S20C steels and S55C steels in order.
    The generation characteristics in AE agreed with the transitional fracture behavior under the changes of testing temperature and were classified into three groups; I) cleavage crack type, II) stable crack growth type, and III) mixed type of I) and II). The AE total count remained constant to KIC up to 40MPa·m1/2, independent of carbon content, and they turned to linear relationship to KC.
    AE characteristics were dependent on the volume fraction ratio of ferrite and pearlite, and reached to maximum when the ratio was close to 1.
  • Fracture Characteristics Evaluation by Charpy Impact Bending Test

    pp. 860-869

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    Charpy impact bending test is a rapid inexpensive test for determining fracture characteristics.
    Load-time relationships from instrumented Charpy test and their temperature dependency were discussed from a viewpoint of evaluating the fracture characteristics. V-notched and fatigue pre-cracked low carbon steel specimens were tested in the range from liquid nitrogen temperature to room temperature. Slow tensile tests and slow bending tests with Charpy-type specimens were also done in the same temperature range. To evaluate the plane strain fracture toughness, the fatigue pre-cracked specimen was desirable. Absorbed energy in pre-cracked impact test could be used for KIC evaluation under a limitation. The varidity of KIC evaluated could be mostly inspected by the form of the loadtime curve. JIC and COD will be obtained using this test. The loading rate has a small effect on fracture characteristics, and since the values evaluated by Charpy impact test are expedient measures the loading rate effect on them is negligible. Dynamic yield strength and microscopic fracture strength could be given by the instrumented v-notched Charpy test result. To improve this test, the more accurate load measurement is required, while the displacement observation is useless.
  • Fracture Toughness of Turbine Rotor Material Around Room Temperature and Validity Criterion for Plane Strain Fracture Toughness

    pp. 870-876

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    The plane strain fracture toughness of 2.8%Ni-Cr-Mo-V steels was evaluated at the lowest service temperature (around room temperature) using huge size specimen with 345mm in thickness and 920mm in diameter, probably the largest fracture toughness specimen ever tested inthe world.
    The validity criterion for KIC has been investigated by using various sizes of compact tension specimens.
    It is proposed that KIC can be obtained when only the condition of Pmax=PO is satisfied, namely the linear relationship between load and displacement is maintained.
  • Evaluation of JIC Fracture Toughness of Nuclear Reactor Pressure Vessel Steels by Three-Point Bend Specimens

    pp. 877-890

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    Four methods for determining JIC value using small specimens are compared on A533B Cl. 1 steel (HSST 03 Plate). Three-point bend tests are carried out at temperatures between-65 and 70°C. The crack initiation point on a load-deflection curve is determined by an electrical potential method. Besides this, precracked Charpy type specimens of A533B Cl. 1 and A542 steels are tested using the R-curve method to clarify the relation between the J integral value and COD value. The test results obtained are as follows:
    (1) The method proposed by RICE is the most useful with respect to its simplicity, accuracy, and requirement of only one specimen.
    (2) The specimen size requirement for a valid JIC value can be described by the following equation; B≥25 (JY) where B is the specimen thickness and δY is the yield strength.
    (3) The empirical results obtained with small specimens are in good agreement with those obtained with large ones.
    (4) The blunting line used in the R-curve method can be described by the following equation; J=3.7δYΔa where δY is the yield strength and Δa is the crack extension.
    (5) J value, COD, and lateral contraction, LC are related with each other as follows; JY=2.6 (COD) JY=2.0 (LC) COD=0.77 (LC)
  • Evaluation of Fracture Toughness of Structural Steels Through J Integral

    pp. 891-898

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    J integral, KIC and COD values were measured and compared with each other on four structural steels, HT80, HT60, KD32 and SM41C. These fracture toughness parameters were obtained through three-point bend tests conducted at low temperatures varying from liquid nitrogen temperature to 0°C.
    The main results obtained are as follows:
    1) The KIC value calculated from JIC is in good agreement with that obtained according to ASTM standard.
    2) The COD value calculated from J integral value through Dugdale's model is approximately 1.4 times the empirical one regardless material, specimen thickness and temperature.
    3) Equivalent energy method using JC value gives a good estimation of fracture stress of a deepnotched, tensile specimen.
    4) Fracture stress calculated from KIC or J integral value is greater than that from a COD value through Dugdale's model. The difference between them becomes greater as the plate thickness becomes greater and the temperature lower.
  • Hydrogen Embrittlement of High Strength Steels in High Pressure Hydrogen Gas at Ambient Temperature

    pp. 899-905

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    It is well known that the ductility and notched tensile strength of steels are reduced in high pressure hydrogen gas. Since some high strength steels are used for the vessels to contain high pressure hydrogen gas, it is important to study this embrittlement phenomenon for the safety of the vessels. From this point of view, the steels generally used for vessels, AISI 4340, AISI 4130 and a high manganese steel were tested in hydrogen gas at 200kg/cm2 and their embrittlement phenomena were investigated by means of fracture mechanics. In addition, the fracture morphology was observed by the scanning electron microscope and the following results were obtained.
    (1) Critiral stress intensity factor (KH) of the steels increases rapidly when the strengths become lower than 90kg/mm2 by tempering.
    (2) The fracture morphology changes from hydrogen embrittlement quasi-cleavage fracture to intergranular fracture as the stress intensity factor decrases or the strength of the steels increases.
    (3) From comparison with other environments to cause hydrogen embrittlement, it is realized that the high pressure (200kg/cm2) hydrogen gas is a severe emvironment almost corresponding to the pure water saturated with H2S.
  • Factors Controlling Fracture Toughness

    pp. 906-916

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  • Mechanical Aspects of Fracture Toughness Evaluation

    pp. 917-924

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  • Fractography and Fracture Mechanics of Fracture of Steels

    pp. 925-936

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    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • A Study of Shear Crack Propagation in Spring-loaded DCB Testing

    pp. 937-946

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    The research of shear crack propagation with high velocity by spring-loaded DCB testing has a definite objective of obtaining the fracture criterion as well as the material resistance against fracture propagation, which is inseparably related to the establishment of design philosophy against unstable ductile fracture of highly pressurized gas pipelines.
    The experiments and analyses were performed by DCB testing with several types of specimen geometry as well as with different spring compliances on wide variety of steels. It has been derived that the critical parameter, δc/t (crack opening displacement/material thickness), is a material resistance which is independent of specimen geometry (including curvature of groove), and of spring compliance.
    It is also shown that the parameter, δc/t, is closely related to the fracture strain at the tip of running shear crack and that the criterion explains well the measured plastic zone width with a simple supplementary calculation. The comparison between the spring-loaded DCB testing with full-scale burst testing of pipelines has been done, using the available data, by estimating the plastic zone width in full-scale testing or by correlating the Jc value with Charpy energy in both testing. The effects of compliance in the springloaded DCB testing are also discussed.
  • Laboratory Test for Unstable Ductile Fracture

    pp. 947-957

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    A laboratory test for unstable ductile fracture of mild steels was developed. Shear crack was initiated from very deep notch. Some devices such as “pipe tabs” were employed to reduce the stiffness of the system enough to make shear crack continue to grow in an unstable manner.
    Four kinds of pipe materials were tested using the present test method and three kinds of them with low ductility showed unstable ductile fracture. Fracture toughness for the onset of unstable ductile fracture in these steels was evaluated and was correlated successfully to Cvshelf, upper shelf of absorbed energy in Charpy test.
    Slow crack growth test was also performed by means of high stiffness tensile system, “R-cruve” to ductile crack growth being obtained experimentally. A model to ductile crack growth was proposed by the use of the modification of Dugdale model, by which R-curves were finely described. Critical G-values for the onset of the unstable ductile crack propagation were shown to be well compared to the values estimated from the R-curves.
    Thus, both the ductile slow growth and its rapid propagation are shown to be well characterised by the values of notch ductility.
  • On the Propagating Shear Fracture in Large Diameter Gas Pipeline

    pp. 958-968

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    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Effect of Post-weld Heat Treatment on the Fracture Mechanics Behaviour for Electroslag Welding Joints of SM41B Heavy Thickness Plate

    pp. 969-978

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    The effect of post welding heat treatments on the notch toughness and fracture mechanics behaviour of 110mm thick JIS SM41B steel electroslag welding joints has been investigated. The results obtained are summarized as follows:
    1. Notch toughness of welded joints normalized became excellent in heat-affected zone, but in weld metal it became lower. In case of stress relief annealed condition weld metal showed best notch toughness. This reason is considered to the variation of microstructure.
    2. Fracture toughness values (KIC) of welded joints showed an excellent trend in heat-affected zone with both normalized and stress relief annealed conditions.
    3. Fatigue crack growth property of welded joints under stress relief annealed condition was more excellent than those of normalized joints and base metal.
    4. There was good correlation between KIC and Charpy transition temperature for both base metal and its welded joints.
    5. Dynamic fracture toughness values (KId) estimated by instrumented Charpy tests can be correlated with static fracture toughness values (KIC) by rate parameter theory.
  • Fracture Toughness in Heat-Affected Zone Subjected to Stress Relief Annealing

    pp. 979-989

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    Transition curves of Charpy impact value and COD were measured on high strength steels, HT60 and HT80, which were subjected to synthetic welding thermal cycle and SR (stress relief) annealing at 600°C and 650°C. The cooling rate of welding thermal cycle was chosen so as to give not so different hardness between “as welded” and “SR” conditions in the same steel. The following conclusions are obtained.
    (1) Specimen HT-80 stress-relieved at 600°C suffers from temper embrittlement characterized by intercrystalline fracture and high fracture-appearence transition temperature vTrs., in Charpy impact test. Other specimens fracture in a cleavage mode at low temperature.
    (2) The temperature at which COD assumes 0.10 mm, δT0.10, is set to be a measure of brittle fracture initiation temperature. δT0.10 was found to be much lower than that predicted from vTrs in the specimen of intercrystalline fracture type. On the other hand, evaluation of toughness depends not so much on which measure vTrs or δ0.10 is employed in specimens of cleavage fracture type.
    (3) It was found that the high dependency of fracture appearance transition temperature on strain rate is a cause of the extra-ordinary relation between vTrs and δT0.10 in specimens of intercrystalline fracture type. Then it can be concluded that an appropriate strain rate should be selected in toughness test in accordance with the service condition of the objective steel structure.
    x

    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Evaluation Methods of Fracture Toughness of Structural Steels and Significance of Defects in Welded Structures

    pp. 990-1000

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  • Application of the 80kg/mm2 Class High Strength Steel to Welded Structure

    pp. 1001-1019

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  • Fracture and Its Analysis

    pp. 1020-1030

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    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Strength and Low Temperature Toughness of Fe-13%Ni-Mo Alloys

    pp. 1031-1037

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    Mechanical tests were made on newly developed Fe-13%Ni-Mo alloys for cryogenic service. The effects of the additional elements were investigated from the viewpoint of the strength and the low temperature toughness. The alloys added by Al, Ti or V have the better balance of these properties. They did not show low temperature brittleness induced by cleacage fracture in Charpy impact test at 77 K. The microfractography showed the utterly dimple rupture patterns on the broken surface of all specimens. It would be supposed that the cleavage fracture stress is considerably higher than the flow stress. These alloys are superior to some commercial structural materials for low temperature use in the balance between the strength at 300 K and the toughness at 77 K. Additionally, it is noted that these experimental alloys have a good advantage in getting high strength and high toughness by the rather simple heat treatment.
  • Fracture Toughness of Fe-13%Ni-3%Mo-0.2%Ti Alloy at Cryogenic Temperature

    pp. 1038-1046

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    Fracture tests at cryogenic temperature were carried out on Fe-13%Ni-3%Mo-0.2%Ti alloy for cryogenic service. The results showed that this alloy did not yield cleavage fracture even at 4 K. The temperature dependence of the fracture toughness was smaller than those of the yield and the tensile stress. The clear transition temperature was not observed down to 4 K. The ductile-brittle transition temperature decreased with Ni concentration in B.C.C. iron (α-iron) alloy and was extrapolated to 0 K at about 13% of Ni. This estimated value agreed with the results obtained by Charpy impact test.
    The structural materials for cryogenic use should possess high strength and toughness for salty at lower temperature. The yield stress (proof stress) and the fracture toughness of this alloy were 750 MPa at 300K and 90 MPa√m at 4 K, respectively. The good balance between them was satisfied in this alloy.
  • Plane Strain Fracture Toughness and Stretched Zone of an 18%Ni Maraging Steel with Various Prior-Austenite Grain Sizes

    pp. 1047-1055

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    The effect of prior austenite (γ) grain or martensite (α') packet size on the plane strain fracture toughness (KIC) and the correlation between the stretched zone width and KIC of an 18% Ni maraging steel were studied by means of fracture toughness testing and fractography.
    KIC was not affected by γ grain size in the fine (6.7-15.7μ) or coarse (118μ) region, while it increased in the intermediate grain size range from 28.3 to 90.4μ. In the latter condition, the plastic zone spread over about one to tow α' packets ahead of the fatigue pre-crack before the onset of unstable fracture.
    Stretched zone was observed at the tip of the fatigue pre-crack, and the zone width related linearly to the critical crack opening displacement. The width of the stretched zone was increased by the enhanced relaxation of the stress concentration by the micro-cleavage nucleation after the spreading of the plastic zone over about one to two α' packets.
    It seemed that the enhanced blunting process of the fatigue crack led to the increment in KIC. On the other hand, KIC was independent of such a structural unit as γ grain or α' packet when the enhanced blunting effect was not introduced.
    x

    Readers Who Read This Article Also Read

    1. Heat Transfer Phenomena in Immersion Cooling of Heated Steel Plate and Influence of Water Stirring on Heat Transfer Tetsu-to-Hagané Vol.64(1978), No.1
    2. 第97回講演大会討論会講演概要 Tetsu-to-Hagané Vol.65(1979), No.2
    3. 第95回講演大会討論会講演概要 Tetsu-to-Hagané Vol.64(1978), No.2
  • Effects of Aging Conditions and Strain Rate on Elongation of 245kg/mm2 Grade and 210kg/mm2 Grade Maraging Steels

    pp. 1056-1062

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    Tensile strength and elongation of 18% Ni-type maraging steels, the nominal strength levels of which are 245kg/mm2 and 210kg/mm2, have been investigated as a function of aging time. The temperature range in aging was from 575°C to 400°C. A cross-head speed in the tensile test was varied from 1.0mm/min to 0.005mm/min. The change in electrical resistivity at liquid nitrogen temperature has also been measured.
    Brittle fracture which is caused by decreasing the cross-head speed is observed in the 245kg/mm2 grade maraging steel in the early stage of aging in the temperature range from 500°C to 400°C. The decrease in elongation is also observed in the tensile test of the cross-head speed of 0.005mm/min in the 210kg/mm2 grade maraging steel in the early stage of aging from 425°C to 400°C. The brittle behavior in low strain rates is reduced by prolonging aging time. Activation energy is calculated to be about 80 kcal/mol for the 245kg/mm2 grade maraging steel from the relation between reciprocal absolute aging temperatures and times giving the removal of the brittle behavior at the cross-head speed of 0.005mm/min. It is noted that aging temperature and time are important for the removal of the brittle behavior in low strain rates.
  • Relation of Processing Variables in Thermomechanical Treatment to Strength, Ductility, and Toughness of 280kg/mm2 Grade Maraging Steel

    pp. 1063-1071

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    In order to produce the ultrahigh strength maraging steel plate with excellent ductility and toughness, and free from the anisotropy in the maechanical properties, the effects of processing variables in thermomechanical treatment on the mechanical properties of 13Ni-15Co-10Mo steel have been investigated. The relation between prior austenite gtain size and the mechanical properties has also been investigated. The austenite grain size attainable is greatly affected by the reduction in rolling. The grain refinement increases the tensile strength and ductility, but does not improve fracture thoughness. The anisotropies of strength and ductility are found to be related to the occurrence of the unrecrystallized austenite grain, whereas the anisotropy of fracture toughness is not observed for all the conditions. Thus, the recrystallized and fine grained structure is found favorable to produce the excellent combination of the strength, ductility, and isotropy. Such a microstructure is produced by choosing the optimum conditions in the thermomechanical treatment, which involve the rolling temperature and reduction.
  • Influences of Strength and Non-Metallic Inclusion on the Fatigue Crack Propagation Characteristics in Structural Steels

    pp. 1072-1081

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    Fatigue crack propagation rates were obtained for structural steels having tensile strength levels ranging from 40 to 100kg/mm2. The constant m in the Paris' formula, da/dN=C (ΔK) m, was found to decrease with increase in the yield strength of the steel. The influence of m on the fatigue crack propagation life was analysed for the case of center through-notched plate as well as part through-notched plate. Both experiments and calculations showed that the higher strength steels endured longer than the lower strength steels when cracks were large and/or stress ranges were high, however, they endured shorter when cracks were small and/or stress ranges were low.
    When steel plates were fatigued under through-thickness stresses, m increased with increase in sulphur content, though the strength levels of steels were identical. This phenomenon was quantitatively analysed on the basis of the proposed model that sub-cracks initiating from MnS inclusions near the main crack accelerated the fatigue crack propagation rate.
    The endurance limits in through-thickness fatigue were correlated with the projection length of inclusions based on the existance of the threshold range of stress intensity factor, ΔKth, in the fatigue crack propagation rate ΔK diagram.
  • Initiation and Propagation of Microcracks in SNCM8 Steel Fatigued under Combined Axial Loading and Torsion

    pp. 1082-1093

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    The behavior of initiation and propagation of cracks on quench-tempered SNCM8 steel fatigued under combined axial loading and torsion was investigated in particular relation to the inhomogeneity of metallurgical structure. The main conclusions are as follows:
    (1) An inhomogeneous structure was produced in the steel as a result of segregation of manganese and the lower hardness constituent of the structure determined the fatigue strength of the steel.
    (2) The stage 1 cracks tended to form along the maximum shear stress plane and to be more localized in the lower hardness constituents as τaa-ratio became higher, where τa and σa were shear stress and axial stress amplitudes, respectively.
    (3) The threshold amplitude of stress intensity for Mode I crack, KIath, was 5.07 MPa√m and that for Mode II crack, KIIath, was 12.4 MPa√m.
    (4) When τaa≤1/√3, the specimens were fractured by the preferential propagation of Mode I crack originating from non-metalic inclusions. The critical length of Mode I propagating crack at the fatigue limit was observed to be about 0.1 mm. This agreed with an estimation by using the KIath value. When τaa≥√3, the fatigue limit coyresponded to the critical stfess amplitude below which plastic strain amplitude was hardly detectable macroscopically.
  • 抄録

    pp. 1094-1098

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  3. blast furnace permeability
  4. hot rolling
  5. basicity
  6. cohesive zone
  7. alternating current electrolyzing method for colored stainless steel
  8. fe coating
  9. fe nano coating
  10. hole expanding test