소형펀치 시험법을 이용한 INCONEL Alloy 617의 수소취화거동 평가

서현욱,마영화,윤기봉 한국수소및신에너지학회 2010 한국수소 및 신에너지학회논문집 Vol.21 No.4

For the conversion into hydrogen society, not only studying facilities of hydrogen production, storage, transportation and charging system but also developing technique of ensuring safety are essentially needed. Hence, for the first step of that, evaluated the hydrogen embrittlement of Inconel alloy 617, Ni-based super heat-resisting alloy, by small punch test. Prepared the various specimens through changing electrochemical charging time and measured the toughness degradation of the specimens by small-punch test. The analysis of hydrogen embrittlement behavior were carried out by investigating the fractured surface of specimens. This study has significance on revealing mechanism of hydrogen embrittlement behavior and the factor affecting hydrogen embrittlement in the future study.

Taylor 급수를 이용한 617 합금의 장시간 크리프 수명 예측

윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),박재영(Jae-Young Park),김선진(Soen-Jin Kim),김용완(Yong-Wan Kim) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.4

본 연구에서는 McVetty 와 Monkman-Grant 의 모델에 기초하여 만들어진 새로운 크리프 수명예측 모델인 Taylor 급수(T-S) 모델을 제안하였다. 본 모델은 회귀분석에서 발생하는 오차를 줄이기 위하여 McVetty 모델에서 sinh 함수를 Taylor 급수에 의해 변환한 후 첫 3 개항을 취한 것으로서 모델중의 상수 값은 통계학적 방법인 최대가능성 기법을 이용하여 결정되었다. T-S 모델을 이용하여 Alloy 617 의 크리프 수명을 예측한 결과 Eno, 지수함수 및 Larson-Miller(L-M) 방법에 비해 더 정확한 예측을 하는 것으로 나타났다. 또한 T-S 모델은 특정 온도에서 크리프 수명 예측을 할 수 있는 등온 T-S(IT-S) 모델로 표현될 수 있었으며, IT-S 모델은 Alloy 617 의 장시간 크리프 수명예측에서 가장 좋은 예측을 하는 것으로 나타났다. In this study, a Taylor series (T-S) model based on the Arrhenius, McVetty, and Monkman-Grant equations was developed using a mathematical analysis. In order to reduce fitting errors, the McVetty equation was transformed by considering the first three terms of the Taylor series equation. The model parameters were accurately determined by a statistical technique of maximum likelihood estimation, and this model was applied to the creep data of alloy 617. The T-S model results showed better agreement with the experimental data than other models such as the Eno, exponential, and L-M models. In particular, the T-S model was converted into an isothermal Taylor series (IT-S) model that can predict the creep strength at a given temperature. It was identified that the estimations obtained using the converted ITS model was better than that obtained using the T-S model for predicting the long-term creep life of alloy 617.

Alloy 617 확산용접재의 상온 저주기피로 거동

박재환(Jaehwan Park),김선진(Seon-Jin Kim),사인진(Injin Sah),김응선(Eung-Seon Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

초고온가스로의 중간열교환기로 인쇄기판형열교환기 타입이 고려되고 있다.^(1-3) 기계적 물성이 우수한 확산용접 방법이 인쇄기판형열교환기 제작에 이용될 것으로 예상된다.⁽⁴⁾ 본 연구는 상온에서 Alloy 617 확산용접재의 저주기피로 거동을 평가했다. 미국기계학회 표준시험법 E606-19에 따라 제작한 버튼헤드형 시편을 이용하였으며, 변형률 속도 3×10^-3 /s 에서 저주기피로 시험을 수행하였다. 저주기피로 시험에 사용된 전변형률 범위는 0.9, 1.2 및 1.5%이다. 삼각파하중 형상을 갖는 완전양진(R=-1) 변형률제어 방법이 사용되었다. 전변형률 범위가 증가함에 따라 피로수명이 감소하였고, 모든 전번형률 범위에서 최대 및 최소 응력이 대칭이었다. 모든 전변형률 범위에서 초기에 반복경화가 발생하였고, 일정 주기 이후 반복연화를 보였다. 확산용접재의 피로수명은 모재의 60~80%임을 확인하였다. 확산용접재 시편의 파손은 표점영역 내 접합계면과 떨어진 지점에서 발생하였다. A printed circuit heat exchanger (PCHE) type is considered for an intermediate heat exchanger (IHX) in a very high temperature gas-cooled reactor.^(1-3) Diffusion welding method which has superior mechanical properties is expected to manufacture PCHE.⁽⁴⁾ In this study, low cycle fatigue behavior of diffusion-welded Alloy 617 was evaluated at room temperature. Low cycle fatigue test was conducted at a strain rate of 3×10^-3 /s with button head type specimen in accordance with standard ASTM: E606-19 in American Society for Testing and Materials (ASTM). Total strain ranges used in the low fatigue test are 0.9, 1.2 and 1.5%. Triangular waveform with fully reversed (R=-1) strain-controlled method was employed. The fatigue life decreased as the total strain range increases, and peak-valley stresses were symmetric in all total strain ranges. Specimens were cyclic hardened at an early stage, and then cyclic softening occurred after a certain cycle in all test condition. It was revealed that fatigue life of the diffusion weldment was 60-80% of as-received Alloy 617. The failure of the specimens occurred away from the interface in the gauge section.

초고온가스로용 Alloy 617의 불순물 함유 헬륨/공기 중에서 고온부식 특성

정수진 ( Su Jin Jung ),이경근 ( Gyeong Geun Lee ),김동진 ( Dong Jin Kim ),김대종 ( Dae Jong Kim ) 한국부식방식학회 2013 Corrosion Science and Technology Vol.12 No.2

A very high-temperature gas reactor (VHTR) is one of the next generation nuclear reactors owing to its safety, high energy efficiency, and proliferation-resistance. Heat is transferred from the primary helium loop to the secondary helium loop through an intermediate heat exchanger (IHX). Under VHTR environment Alloy 617 is being considered a candidate Ni-based superalloy for the IHX of a VHTR, owing to its good creep resistance, phase stability and corrosion resistance at high temperature. In this study, high-temperature corrosion tests were carried out at 850 - 950℃ in air and impure helium environments. Alloy 617 specimens showed a parabolic oxidation behavior for all temperatures and environments. The activation energy for oxidation was 154 kJ/mol in helium environment, and 261 kJ/mol in an air environment. The scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS) results revealed that there were a Cr-rich surface oxide layer, Al-rich internal oxides and depletion of grain boundary carbide after corrosion test. The thickness and depths of degraded layers also showed a parabolic relationship with the time. A corrosion rate of 950℃ in impure helium was higher than that in an air environment, caused by difference in the outer oxide morphology.

950℃ 순수헬륨 분위기에서 크리프 파단된 Alloy 617의 미세구조적 고찰

이경근,정수진,김대종,김우곤,박지연,김동진,Lee, Gyeong-Geun,Jung, Su-Jin,Kim, Dae-Jong,Kim, Woo-Gon,Park, Ji-Yeon,Kim, Dong-Jin 한국재료학회 2011 한국재료학회지 Vol.21 No.11

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

니켈기 합금 Alloy 617의 950℃ 대기/헬륨 분위기에서 산화거동 고찰

정수진 ( Sujin Jung ),이경근 ( Gyeong-geun Lee ),김동진 ( Dong-jin Kim ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.5

Alloy 617 is a candidate Ni-based superalloy for intermediate heat exchanger (IHX) of a high-temperature gas reactor (VHTR), because of its good creep strength and corrosion resistance at high temperature. Small amount of impurities such as H₂O, H₂, CO and CH₄ are introduced inevitably in helium, as a coolant during operation of a VHTR. Reactions of material and impurities are accelerated with increase of temperature to 950℃ of operating temperature of a VHTR, leading to material corrosion aggravation. In this circumstance, high-temperature corrosion tests were performed at 950℃ in air and impure helium environments, up to 250 hours in this study. Oxidation rate of 950℃ in an air environment was higher than that of impure helium, explained by difference in outer oxide morphology and microstructure as a function of oxygen partial pressure. An equiaxed Cr-rich surface oxide layer was formed in an air environment, and a columnar Cr-rich oxide was formed in an impure helium environment.

Alloy 617 의 장시간 크리프 수명 예측을 위한 다중회귀 선형 모델의 제안 및 평가

윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),정익희(Ik-Hee Jung),김용완(Yong-Wan Kim) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.4

Creep life prediction has been commonly used by a time-temperature parameter (TTP) which is correlated to an applied stress and temperature, such as Larson-Miller (LM), Orr-Sherby-Dorn (OSD), Manson-Haferd (MH) and Manson-Succop (MS) parameters. A stress-temperature linear model (STLM) based on Arrhenius, Dorn and Monkman-Grant equations was newly proposed through a mathematical procedure. For this model, the logarithm time to rupture was linearly dependent on both an applied stress and temperature. The model parameters were properly determined by using a technique of maximum likelihood estimation of a statistical method, and this model was applied to the creep data of Alloy 617. From the results, it is found that the STLM results showed better agreement than the Eno’s model and the LM parameter ones. Especially, the STLM revealed a good estimation in predicting the long-term creep life of Alloy 617.

Creep Crack Growth Behavior at High Temperatures of Alloy 617

Woo-Gon Kim(김우곤),Jae-Young Park(박재영),I.M.W. Ekaputra,Seon-Jin Kim(김선진),Eung-Seon Kim(김응선) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Alloy 617 is a major candidate material for use of the intermediate heat exchanger (IHX) of a very high temperature reactor (VHTR) system, which is designed to be used for a 60 year lifetime at a high temperature. Creep crack growth (CCG) behavior as well as creep deformation, due to creep damage during the long service life at elevated temperatures, is very important. However, the CCG design data to meet the needs of the conceptual designers and/or to develop ASME design code of VHTR system are not available elsewhere. In this study, a series of experimental CCG data was obtained from the CCG tests performed under different applied loads at 800 and 850oC for Alloy 617. The CCG behavior was evaluated in terms of the C<SUP>*</SUP> fracture parameter, and the CCG laws for the two temperatures were proposed and fracture microstructures were observed and discussed.

Alloy 617의 850℃ 에서 공기 및 헬륨 분위기 크리프 파단 특성

김우곤(Woo-Gon Kim),박재영(Jae-Young Park),이경근(Gyeong-Geun Lee),홍성덕(Sung-Deok Hong),김용완(Yong-Wan Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.4-2

Experimental creep data for Alloy 617 in the air and He environments at 850°C was obtained under different applied stresses. Alloy 617 followed Norton’s power law and the Monkman-Grant relationship well. There were no large differences in the shapes of the creep curves between the air and He environments. The minimum creep rate and rupture time in the He environment were almost similar to those in the air one. As the stress decreased, the creep ductility decreased significantly. The oxide layer thickness in the He environment was a little higher than that in the air one. However, it was found that creep rupture time was closely related to oxide layer thickness, because the thickness of the outer and internal oxide layers between the air and He environments did not reveal a large difference.

Taylor 급수를 이용한 Alloy 617 의 장시간 크리프 수명 예측 모델의 적용성

윤송남(Song-Nan Yin),김우곤(Woo-Gon Kim),박재영(Jea-Yeong Park),김용완(Yong-Wan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

Creep life prediction has been commonly used by a time-temperature parameter (TTP) which is correlated to a rupture time and temperature, such as Larson-Miller (LM), Orr-Sherby-Dorn (OSD), Manson-Haferd (MH) and Manson-Succop (MS) parameters. A Taylor series model(T-SM) based on Arrhenius, McVetty and Monkman-Grant equations was newly proposed through a mathematical procedure and in order to reduce the fitting errors the McVetty’s equation was transformed by taking the first three-terms of Taylor series equation. The model parameters were properly determined by means of a technique of maximum likelihood estimation of statistical method, and this model was applied to the creep data of Alloy 617. The T-SM results revealed better agreement than the Eno’s model and the LM parameter one. Especially, it was identified that the T-SM showed a good estimation in predicting the long-term creep life of Alloy 617.