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미소시험편에 의한 재질열화된 내열강의 고온 크리프 특성 평가
류대영,백승세,유효선,Lyu, Dae-Young,Baek, Seung-Se,Yu, Hyo-Sun 한국재료학회 2003 한국재료학회지 Vol.13 No.7
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.
슈퍼 오스테나이트 스테인리스강의 열화손상에 대한 비파괴적 평가
권일현,백승세,유효선,Kwon, Il-Hyun,Baek, Seung-Se,Iino, Y.,Yu, Hyo-Sun 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.7
This research was undertaken to clarify effects of thermal aging on electrochemical and mechanical properties of superaustenitic stainless steel and to detect the material degradation nondestructively. The steel was artificially aged at $300{\sim}650^{\circ}C$ for $240{\sim}10,000h$ and the mechanical properties were investigated at $-196{\sim}650^{\circ}C$ using small punch(SP) test. Also, the change in electrochemical properties caused by effects of thermal aging on superaustenitic stainless steel was investigated using electrochemical anodic polarization test in a KOH electrolyte. Carbides and ${\eta}-phase(Fe_2Mo)$ precipitated in the grain boundaries seem to deteriorate the mechanical properties by decreasing cohesive strength in the grain boundaries and to promote the current density observed in electrochemical polarization curves, The electrochemical and mechanical properties of superaustenitic stainless steel decreased significantly in the specimen aged at $650^{\circ}C$ corresponding to the sensitization temperature for conventional austenitic stainless steels.
전기화학적 재활성화 분극시험에 의한 터빈부재의 열화손상 평가
권일현,백승세,류대영,유효선,Kwon, Il-Hyun,Baek, Seung-Se,Lyu, Dae-Young,Yu, Hyo-Sun 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.7
The extent of materials deterioration can be evaluated accurately by mechanical test such as impact test or creep test. But it is almost impossible to extract a large test specimen from in-service components. Thus material degradation evaluation by non-destructive method is earnestly required. In this paper, the material degradation for virgin and several aged materials of a Cr-Mo-V steel, which is an candidated as structural material of the turbine casing components for electric power plant, is nondestructively evaluated by reactivation polarization testing method. And, the results obtained from the test are compared with those in small punch(SP) tests recommended as a semi-nondestructive testing method using miniaturized specimen. In contrast to the aged materials up to 1,000hrs which exhibit the degradation behaviors with increased ${\Delta}[DBTT]_{SP}$, the improvement of mechanical property can be observed on the 2,000hrs and 3,000hrs aged materials. This is because of the softening of material due to the carbide precipitation, the increase of ferritic structures and the recovery of dislocation microstructure by long-time heat treatment. The reactivation rates($I_R/I_{Crit},\;Q_R/Q_{Crit}$) calculated by reactivation current densityt ($I_R$) and charge($Q_R$) in the polarization curves exhibit a good correlation with ${\Delta}[DBTT]_{SP}$ behaviors.
고 Cr-Mo강의 수정멱수법칙을 이용한 W.M. 크리프 수명예측
안종교(Jong Kyo An),유효선(Hyo Sun Yu),양성모(Sung Mo Yang),강희용(Hee Yong Kang) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.11
The high temperature creep properties of the generating plant's high temperature tube, pipe and header and such are very significant in accordance with long-time exposure to the high temperature and pressure environment. Not only this, but as the welding procedure is compulsory for the cohesion of components, the creep properties regarding the local microstructures of steel weldment are very important. In order to understand the creep properties regarding the local microstructures of steel weldment, the SP-Creep test which is easy to get sample from the field component was conducted. The local microstructure of steel weldment, that is, W.M. and B.M.'s microstructures were observed using the SEM. The rupture time of W.M. was longer as 110 % averagely in a same condition, which is the consequence of the difference of the microstructure. Each lethargy coefficient of B.M. and W.M. is evaluated by the relation among the temperature, load and the rupture time from SP-Creep Test. The life estimation equation can be induced by the transformation of Power-law. B.M. and W.M. for each 550 ℃ and 575 ℃, the very similar to normal temperature of the domestic thermal power generation in working, are estimated.
양성모(Sung Mo Yang),유효선(Hyo Sun Yu),이용준(Yong Jun Lee),송준혁(Joon Hyuk Song),오제하(Je Ha Oh) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.5
In order to develop a mower attached to the front of speed sprayer, a mowing part was developed separately for power operation. A prototype mower is composed of height adjusting wheels, straight blades(600 mm), gasoline engine(16HP) and the attachment to a speed sprayer. The FE modeling of frame panel is implemented. The maximum Von-Mises stress is 39.33 Mpa at hydraulic system and minimum Von-Mises stress is 0.02 Mpa at the center of frame panel. A safety factor of 6.3 would be adequate for a drive component in a mower.
소형펀치-크리프 시험에 대한 응력해석과 일축 크리프 시험과의 상관성에 관한 연구
이송인,백승세,권일현,유효선,Lee, Song-In,Baek, Seoung-Se,Kwon, Il-Hyun,Yu, Hyo-Sun 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.12
A basic research was performed to ensure the usefulness of Small Punch-creep(SP-creep) test for residual life evaluation of heat resistant components effectively. This paper presents analytical results of initial stress and strain distributions in SP specimen caused by constant loading for SP-creep test and its experimental correlations with uniaxial creep(Ten-creep) test on 9Cr1MoVNb steel. It was shown that the initial maximum equivalent stress, ${\sigma}_{eq{\cdot}max}$ from FE analysis was correlated with steady-state equivalent creep strain rate, ${\epsilon}_{qf-ss'}$ rupture time, $t_r$, activation energy, Q and Larson-Miller Parameter, LMP during SP-creep deformation. The simple correlation laws, ${\sigma}_{sp}-{\sigma}_{TEN}$, $P_{sp}-{\sigma}_{TEN}\; and\; Q_{sp}-Q_{TEN}$ adopted to established a quantitative correlation between SP-creep and Ten-creep test data. Especially, the activation energy obtained from SP-creep test is linearly related to that from Ten-creep test at $650^{\circ}C$ as follows : $Q_{SP-P}\;{\risingdotseq}\;1.37 \;Q_{TEN},\; Q_{SP-{\sigma}}{\risingdotseq}1.53\; Q_{TEN}$.