• Title/Summary/Keyword: Miniaturized Specimen

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Normalization of DBTT Size Effect far Aged 1Cr-lMo-0.25V Steel (열화된 1Cr-1Mo-0.25V강의 DBTT 크기효과 보정에 관한 연구)

  • Nam, Seung-Hun;Kim, Eom-Gi;Lee, Dae-Yeol
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.12
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    • pp.2109-2115
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    • 2001
  • Miniaturized specimen technology is useful to characterize the mechanical behavior when it is difficult to sample the material enough for the test. In this study, two kinds of miniaturized Charpy impact specimens(i.e., miniaturized specimen with side groove and without side groove) of aged 1Cr- lMo-0.25V steel were prepared and tested. The relationship between the extent of degradation in terms of ductile brittle transition temperature(DBTT) and the fracture stress of 1Cr-1Mo-0.25V steel was established. The fracture stress obtained from miniaturized specimen without side groove turned out to be linearly related with the DBTT of standard specimen. Therefore the fracture toughness of aged turbine rotor steel might be evaluated by the fracture stress. In addition, the correlation between DBTT of standard specimen and that of miniaturized specimen was investigated. As the results of normalizing DBTT by maximum elastic tensile stress, the normalized DBTT of miniaturized specimen without side groove allows one to estimate that of standard specimen.

A Study on the Fracture Stress in Miniaturized Charpy Impact Specimens (소형 샤르피 충격시험편에서의 파괴응력에 관한 연구)

  • Nahm, Seung-Hoon;Kim, Am-Kee;Lee, Dae-Yeol;Kim, Si-Cheon
    • Proceedings of the KSME Conference
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    • pp.132-137
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    • 2001
  • Miniaturized specimen technology is useful to characterize the mechanical behavior using a minimum volume of material, because it is almost impossible to sample the conventional specimen for the fracture toughness test without damage to equipment. Test material was 1Cr-1Mo-0.25V steel which was widely used for turbine rotor material. Two kinds of miniaturized impact specimens were prepared, i.e., miniaturized specimen with side groove and without side groove. The correlation between ductile brittle transition temperature(DBTT) of full size impact specimen and that of miniaturized impact specimen was made. The characteristics of miniaturized impact specimens technique as well as fracture stress were discussed. Finally, we concluded that the characteristics of fracture stress change on aging time were similar to that of DBTT.

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Development of Evaluation Technique of High Temperature Creep Characteristics by Small Punch-Creep Test Method (I) - Boiler Superheater Tube - (SP-Creep 시험에 의한 고온 크리프 특성 평가 기술 개발(I) - 보일러 과열기 튜브 -)

  • Baek, Seung-Se;Na, Seong-Hun;Na, Ui-Gyun;Yu, Hyo-Seon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.12
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    • pp.1995-2001
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    • 2001
  • In this study, a small punch creep(SP-Creep) test using miniaturized specimen(10${\times}$10${\times}$0.5mm) is described to develop the new creep test method for high temperature structural materials. The SP-Creep test is applied to 2.25Cr-lMo(STBA24) steel which is widely used as boiler tube material. The test temperatures applied for the creep deformation of miniaturized specimens are between 550∼600$^{\circ}C$. The SP-Creep curves depend definitely on applied load and creep temperature, and show the three stages of creep behavior like in conventional uniaxial tensile creep curves. The load exponent of miniaturized specimen decreases with increasing test temperature, and its behavior is similar to stress exponent behavior of uniaxial creep test. The creep activation energy obtained from the relationship between SP-Creep rate and test temperature decreases as the applied load increases. A predicting equation or SP-Creep rate for 2.25Cr-lMo steel is suggested. and a good agreement between experimental and calculated data has been found.

Development of High Temperature Creep Properties Evaluation Method using Miniature Specimen (미소시험편을 이용한 고온 크리프 특성 평가법 개발)

  • Yu, Hyo-Sun;Baek, Seung-Se;Lee, Song-In;Ha, Jeong-Soo
    • Proceedings of the KSME Conference
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    • pp.43-48
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    • 2000
  • In this study, a small punch creep(SP-Creep) test using miniaturized specimen$(10{\times}10{\times}0.5mm)$ has been described for the development of the newly semi-destructive creep test method for high temperature structural components such as headers and tubes of boiler turbine casino and rotor and reactor vessel. The SP-Creep testing technique has been applied to 2.25Cr-1Mo(STBA24) steel used widely as boiler tube material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. The overall deformations of SP-Creep curves are definitely depended with applied load and creep test temperature and show the creep behaviors of three steps like conventional uniaxial creep curves. The steady state creep rate${\delta}_{ss}$ of SP-Creep curve for miniaturized specimen increases with increasing creep temperature, but the exponential value with creep loading is decreased. The activation energy$(Q_{spc})$ during SP-Creep deformation with various test temperatures shows 605.7kJ/mol that is g.eater than 467.4kJ/mol reported in uniaxial creep test. This may be caused by the difference of stress states during creep deformation In two creep test. But from the experimental results, e.g. SP-Creep curve behaviors, the steady state creep rate${\delta}_{ss}$ with creep temperature, and the exponential value(n) with creep loading, it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material.

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A Study of New Technique Development for Creep Evaluation of Heat Resistant Steel Weldment(I) (내열강 용접부의 크리프 평가 신기술 개발에 관한 연구)

  • 유효선;백승세;권일현;이송인
    • Journal of Welding and Joining
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    • v.20 no.6
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    • pp.30-30
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    • 2002
  • It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen(l0×10×0.5mm). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at 600℃. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

A Study on New Technique Development for Creep Evaluation of Heat Resistant Steel Weldment (I) (내열강 용접부의 크리프 평가 신기술 개발에 관한 연구(I))

  • 유효선;백승세;권일현;이송인
    • Journal of Welding and Joining
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    • v.20 no.6
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    • pp.754-761
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    • 2002
  • It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen($10{\times}10{\times}0.5mm$). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at $600^{\circ}C$. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

High Temperature Creep Characteristics Evaluation for Degraded Heat Resistance Steel of Power Plant by Mini-Specimen (미소시험편에 의한 재질열화된 내열강의 고온 크리프 특성 평가)

  • Lyu, Dae-Young;Baek, Seung-Se;Yu, Hyo-Sun
    • Korean Journal of Materials Research
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    • v.13 no.7
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    • pp.429-435
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    • 2003
  • In this study the new creep test using miniaturized specimen(10${\times}$10${\times}$0.5 ㎣) was performed to evaluate the creep characteristics for degraded materials of 2.25Cr-1Mo steel. For this creep test, the artificially aged materials for 330 hrs and 1820hrs at $630^{\circ}C$ were used. The test temperatures applied for the creep deformation of miniaturized specimens was X$630^{\circ}C$ and the applied loads were between 45 kg∼80 kg. After creep test, macro- and microscopic observation were conducted by the scanning electron microscope(SEM). The creep curves depended definitely on applied load and microstructure and showed the three stages of creep behavior like uniaxial tensile creep curves. The load exponents of virgin, 330 hrs and 1820 hrs materials based on creep rate showed 14.8, 9.5 and 8.3 at $550^{\circ}C$ respectively, The 1820 hrs material showed the lowest load exponent and this behavior was also observed in the case of load exponent based on creep rupture time. In contrast to virgin material which exhibited fined dimple fractography, a lot of carbides like net structure and voids were observed on the fractography of degraded materials.

Transition Temperature Evaluation of 1Cr-1Mo-0.25V Steel Using Miniaturized Charpy Impact Specimen (소형 샤르피 충격시험편을 이용한 1Cr-1Mo-0.25V강의 천이온도 평가)

  • Nahm Seung Hoon;Kim Si Cheon;Lee Hae Moo
    • Journal of the Korean Institute of Gas
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    • v.2 no.4
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    • pp.42-46
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    • 1998
  • Miniaturized specimen technology Permits mechanical behavior to be determined using a minimum volume of material. The technology is useful in case of not collecting a large amount of materials from industrial equipments. Five kinds of accelerated degradation materials were prepared by isothermal aging heat treatment at $630^{\circ}C$. Three kinds of specimens were prepared for impact testing. In order to increase plastic constraint of subsize specimen, side-groove was introduced. Results between subsize and full size impact testing were compared. Size effects correlations were developed for the impact properties of turbine rotor material. These correlations successfully predict the ductile brittle transition temperature (DBTT) of full size Charpy impact specimens based on subsize specimen data.

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Creep Damage Evaluation of High Temperature Material Using Small Punch Test Method (소형펀치실험법을 이용한 고온재료의 크리프 손상 평가)

  • Yu, Hyo-Sun;Lee, Song-In;Baek, Seung-Se;Na, Sung-Hun
    • Proceedings of the KIEE Conference
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    • pp.265-268
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    • 2000
  • In this study, a small punch creep (SP-Creep) test using miniaturized specimen has been described for the development of the new creep test method for high temperature structural components such as headers and tubes of boiler, turbine casing and rotor, and reactor vessel. The SP-Creep testing technique has been applied to 1Cr-0.5Mo steel used widely as boiler header material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. From the experimental results, e.g. SP-Creep curve behaviors, the creep rate in steady state and creep rupture life with test temperature and load, the load exponential value(n, m), the activation energy($Q_{spc}$), the Monkman-Grant relation and the creep life assessment equation etc., it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material such as boiler header.

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A Study on Small Punch-Creep Test Using Finite Element Analysis II (유한요소해석을 이용한 소형펀치-크리프 시험에 관한 연구 (II) - SP-Creep 시험과 일축 크리프 시험의 상관성을 중심으로 -)

  • Lee, Song-In;Kwon, Il-Hyun;Kim, Yon-Jig;Ahn, Byung-Guk;Ahn, Haeng-Keun;Baek, Seung-Se;Yu, Hyo-Sun
    • Proceedings of the KSME Conference
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    • pp.111-116
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    • 2001
  • Small punch-creep(SP-Creep) test technique has been applied for evaluating the creep characteristics for high temperature materials. However, in order to evaluate the damage and predict the remaining life, it is necessary to establish a quantitative correlation between SP-Creep and uniaxial-creep test results. This paper presents analytical and experimental results of useful correlation between SP-Creep and uniaxial-creep properties for 9Cr1MoVNb steel at $600{\sim}650^{\circ}C$ in terms of stress(load) and activation energy during creep deformation. Especially, the activation energy obtained from SP-Creep test is linearly related to that from uniaxial-creep test at $650^{\circ}C$ as follows: $Q_{sp-p}{\fallingdotseq}1.37\;Q_{TEN},\;Q_{sp-{\sigma}}{\fallingdotseq}1.53\;Q_{TEN}$.

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