• Title/Summary/Keyword: Slow Strain Rate Test (SSRT)

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Stress Corrosion Cracking Susceptibility Evaluation by Small Punch Test (소형펀치시험법에 의한 응력부식균열 감수성평가에 관한 연구)

  • 유효선;이송인;정세희
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.8
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    • pp.2033-2042
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    • 1993
  • In conventional SCC susceptibility test, there are constant strain test, constant load test, slow strain rate test(SSRT) and K$_{ISCC}$ test. Among them, the SSRT method is much more aggressive in producing SCC than the other tests, so that the test time of it is considerably reduced. But this SSRT method has mostly been worked using the uniaxial tensile specimen untill now. Therefore, the SSRT method using the tensile specimen(Ten-SSRT) has much difficulty in SCC susceptibility evaluation of a localized region like weldment and the advantage material of high order. Recentely, the small punch(SP) test method using miniaturized small specimen is the very effective test method for fracture strength evaluation of a localized region like weldment and fusion reactor wall irradiated in the nuclear power plant. This paper investigated the possibility of SCC susceptibility evaluation by the SP-SSRT method using the miniaturized small specimen. Therefore, we obtained the result that the SP-SSRT had the possibility for the evaluations of SCC susceptibility for shorter time to corrosive environment compare to Ten-SSRT which was conventional method.

A Study on the Stress Corrosion Cracking Evaluation for Weld Joint of Steel by Using Miniaturized Small Specimen (미소시험편에 의한 강 용접부의 응력부식 균열 평가에 관한 연구)

  • 유효선
    • Journal of Welding and Joining
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    • v.12 no.4
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    • pp.63-75
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    • 1994
  • The conventional SCC(stress corrosion cracking) test methods have much difficulty in evaluating the SCC behaviors of the localized zone like HAZ, bond line and weld metal because of the specimen size. Accordingly, the purpose of this paper is to develop the new SCC test method of the welded zone by evaluating the SCC susceptibility on parent metal and various microstructures of the welded zone by SP(small punch) test method using miniaturized small specimen and SSRT(slow strain rate test) method(SP-SSRT). Besides, this study is to verify the efficiency of the SP-SSRT results through AE(acoustic emission) test which is a useful technique to monitor the microfracture processes of the material. From the results of SCC susceptibility, SEM observation and AE test, it can be concluded that the SP-SSRT test using miniaturized small specimen(10mm*10mm*0.5mm) will be a good test method to evaluate the SCC susceptibility on the local zone such as the welded zone.

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A Study of Hydrogen Embrittlement Limit Potential of Cu-Containing High Strength Low Alloy Steel for Marine Structure by Potentiostatic SSRT Method (정전위 SSRT법에 의한 해양구조물용 Cu함유 고장력저합금강의 수소취성한계전위 규명에 관한 연구)

  • 김성종;박태원;심인옥;김종호;김영식;문경만
    • Journal of Welding and Joining
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    • v.19 no.2
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    • pp.182-190
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    • 2001
  • A marine structural material was well known to have high tensile strength, good weldability and proper corrosion resistance. Cu-containing high strength low alloy(HSLA) steel was recently developed for their purposes mentioned above. And the steel is free about preheating for welding, therefore it is reported that shipbuilding cost by using it can be saved more or less. However the marine structural materials like Cu-containing HSLA steel are being generally adopted with cathodic protection method in severe corrosive environment like natural sea water but the high strength steel may give rise to Hydrogen Embrittlement due to over protection at high cathodic current density for cathodic protection. In this study Cu-containing HSLA steel using well for marine atructure was investigated about the susceptibility of Hydrogen Embrittlement as functions of tensile strength, strain ratio, fracture time, and fracture mode, etc. and an optimum cathodic protection potential by slow strain rate test(SSRT) method as well as corrosion properties in natural sea water. And its corrosion resistance was superior to SS400 steel, but Hydrogen Embrittlement susceptibility of Cu-containing HSLA steel was higer than that of SS400 steel. However Hydrogen Embrittlement of its steel by SSRT method was showed with pheonomena such as decreasing of fracture time, strain ratio and fracture mode of QC(quasi-cleavage). Eventually it is suggested that an optimum cathodic protection potential not presenting Hydrogen Embrittlement of Cu-containing of HSLA steel by SSRT method was from-770mv(SCE) to - 900mV(SCE)under natural sea water.

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EFFECT OF POST-WELD HEAT TREATMENT OF MARINE STRUCTURE STEEL DURING CATHODIC PROTECTION

  • Kim, Seong-Jong;Masazumi Okido;Kim, Jin-Gyeong;Moon, Kyung-Man
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.273-275
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    • 2002
  • The effect of post-weld heat treatment (PWHT) of marine structures steel was investigated at electrochemical viewpoint. In addition, slow strain rate test (SSRT) was carried out to investigate both electrochemical and mechanical properties by PWHT effect during impressed current cathodic protection. The optimum cathodic protection potential by SSRT was -770 mV(SCE). At the applied cathodic protection potential of -770 mV -850 mV(SCE), the fracture morphology was dimple pattern with ductile fracture, while it was transgranular pattern (Q.C: quasi cleavage) under -875 mV(SCE).

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Evaluation of SCC Susceptibility of Weld HAZ in Structural Steel(I) -material properties and strain rate- (강용접부의 응력부식크랙감수성 평가에 관한 연구 I -재료특성과 변형률 속도-)

  • 임재규;정대식;정세희
    • Journal of Welding and Joining
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    • v.11 no.3
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    • pp.48-60
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    • 1993
  • The cause of corrosion failure found in structures or various components operating in severe corrosive environments has been attributed to stress corrosion cracking(SCC)which is resulting from the combined effects of corrosive environments and static tensile stress. Slow strain rate test (SSRT) provides a rapid reliable method to determine SCC susceptibility of metals and alloys for a broad range of application. The chief advantage of SSRT procedures is that it is much more aggressive in producing SCC than conventional constant strain or constant load tests, so that the testing time is considerably reduced. Therefore, in this paper, the combined effects of material properties and strain rate on the tensile ductility and fracture morphology of parents and weldment for SM45C, SCM440 and SM20C steels were examined and discussed in synthetic sea water. The susceptibility of SCC was the most severe under the strain rate of $1.0{\times}10^{-6} sec^{-1}$, and R.O.A. can be used for parent and maximum load for weldment to evaluate the parameter for SCC susceptibility.

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A Study on the Stress Corrosion Cracking Evaluation for Weld Joint of TMCP steel by SP-SSRT Method (SP-SSRT법에 의한 TMCP강 용접부의 응력부식균열 평가에 관한 연구)

  • 유효선;정희돈;정세희
    • Journal of Welding and Joining
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    • v.15 no.1
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    • pp.46-54
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    • 1997
  • The object of this paper is to evaluate SCC(stress corrosion cracking) susceptibility for parent metal and bond line region of weld joints which have the various weld heat input condtions in TMCP(thermo-mechanical control process) steel by SP-SSRT(small punch-slow strain rate test) method. And the SCC test results of TMCP steel are compared with those of the conventional HT50 steel which has te almost same tensile strength level like TMCP steel. The loading rate used was $3\times10^{-4}$mm/min and the corrosive environment was synthetic sea water. According to the test results, in the case of parent metal, TMCP steel showed higher SCC susceptibility than HT50 steel because of the high plastic strain level of ferrite microstructure obtained by accelerated cooling. And in the case of bond line, the both TMCP steel and HT50 steel showed low load-displacement behaviors and higher SCC susceptibility above 0.6. These results may be caused by theembrittled martensite structure on HT50 steel and by the coarsened grain and the proeutectoid ferrite structure obtained by the impart of accelerated cooling effect on TMCP steel.

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Resistance to Hydrogen Embrittlement of Ultra-high Strength Pearlitic Bolt (펄라이트 조직을 갖는 초고강도 볼트의 수소취성 저항성)

  • Ahjeong Lyu;Young-Kook Lee
    • Journal of the Korean Society for Heat Treatment
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    • v.36 no.1
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    • pp.15-21
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    • 2023
  • Recently, ultra-high strength bolts have been developed for weight lightening of a vehicle and fuel efficiency. However, some amount of diffusible H is absorbed into the bolt during its manufacturing process so that H embrittlement (HE) often occurs particularly in high strength bolts with a tempered martensitic microstructure. This brings attention to ultra-high strength pearlitic bolts with a high resistance to HE. Therefore, in this study the HE resistance of the 1.6 GPa grade pearlitic bolt was evaluated through tightening tests and slow strain rate tests (SSRTs), and fracture surfaces of failed bolts were comparatively observed. A critical H content for the tightening test turned out to be ~0.23-0.35 mass ppm. The bolt with a diffusible H content of ~0.35 mass ppm was fractured during the tightening test, showing a quasi-cleavage fracture surface, indicating the occurrence of HE. In addition, the bolt underwent premature elastic failure during the SSRT. This implies that the HE resistance of high strength bolts can be evaluated by both tightening test and SSRT.

A Study on Stress Corrosion Cracking of Fiber Reinforced Composite by Slow Strain Rate Test (저변형률시험법에 의한 섬유강화 복합재료의 응력부식균열에 관한 연구)

  • Lim, Jae-Gyu;Choi, Tae-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.11
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    • pp.3433-3440
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    • 1996
  • This paper was investigation of the stres corrosion cracking(SCC) mechanism and the properties of corrosion fracture surface of glass fiber reinforced plastics(GFRP) produced by hand lay up(HLU) method in synthetic sea water. Test material is GFRP, that was used vinylester type epoxy acrylate resin and an unsaturated polyester as the matrix and the chopped strand mat(CSM) type E-glss fiber as the reinforcement. The slow strain rate test(SSRT) was performed on dry, wet and saturated wet specimens in sea water. Here the pH concentration of synthetic sea water was 8.2 and the strain rate is 1 x $10^{-6}$($sec^{-1}$) and test temperature ranges varied from $-60^{\circ}C$ to $80^{\circ}C$. It could be confirmed the fact that wet specimens tested at a particular test temperature ranges were appeared the eviences of SCC such as con-planar, mirror and hackle zone. Moreover, SCC of GFRP in sea water was characterised by falt fracture surfaces with only small amounts of fiber pull-out, in partial.

Study on Corrosion Characteristics and Stress Corrosion Cracking of the Weldment for HT-60 Steel in Synthetic Seawater

  • Na, Eui-Gyun;Koh, Seung-Ki;Oh, Seok-Hyung
    • Journal of Mechanical Science and Technology
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    • v.14 no.2
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    • pp.152-158
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    • 2000
  • The contents of this paper include the evaluation of corrosion characteristics and the behaviour of stress corrosion cracking (SCC) for the weldment and post weld heat treatment (PWHT) specimen and parent of HT -60 steel using a slow strain rate test (SSRT) in synthetic seawater. Corrosion characteristics were obtained from the polarization curves by potentiostat, and SCC phenomena were evaluated through the parameters such as reduction of area and time to failure by comparing the experimental results in corrosive environment with those obtained in air. Corrosion rate of the weldment was the fastest, followed by parent and PWHT specimen. SCC phenomena between the weldment of HT-60 steel and synthetic seawater were shown. Besides, SCC was dependent upon the pulling speed greatly. Maximum severity of SCC was obtained at a speed of $10^{-6}mm/min$, whereas SCC could not be seen almost at $10^{-4}mm/min$. The resistance to SCC for PWHT specimen was improved considerably compared that of the weldment at $10^{-6}mm/min$. In case of SCC failure, it was verified from SEM examination that brittle mode and lots of pits could be seen at the fractured region near the surface of the specimen.

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A Study on the Corrosion Rehavior and Mechanical Property by SSRTTest of Welding Part of RE36 Steel for Marine Structure (해양구조물 RE36강의 용접부 부식거동 및 SSRT법에 의한 기계적 특성에 관한 연구)

  • 김종성;김진경;김종호;이명훈;김영식;문경만
    • Journal of Advanced Marine Engineering and Technology
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    • v.24 no.4
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    • pp.460-469
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    • 2000
  • A study on the corrosion behavior of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential and corrosion current density measurement of weld metal(WM), base metal (BM) and heat affected zone(HAZ), Al anode generating current and Al anode weight loss quantity in case of cathodic protection. And we carried out slow strain rate test(SSRT) in order to research mechanical properties such as stress at maximum load, percent strain, time to fracture and strain to failure ratio etc and to find out limiting cathodic polarization potential for hydrogen embrittlement with applied cathodic polarization potential. Hardness of HAZ part was the highest among those three parts and also galvanic corrosion susceptibility was the highest in HAZ part among those three parts due to the lowest corrosion potential than other parts. However corrosion current density was the highest in WM part among those three parts. And the optimum cathodic polarization potential showing the best mechanical properties obtained by SSRT method with applied constant cathodic potential was from - 770mV to - 875mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement on the mechanical properties was under - 900mV(SCE).

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