Thermal aging of Gr. 91 steel in supercritical thermal plant and its effect on structural integrity at elevated temperature

원민구,정시화,허남수,김우곤,이형연 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.1

In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 C for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and serviceexposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

Creep Behavior of Diffusion-Welded High-Temperature Alloy at 800℃

사인진,황종배,박재환,김응선 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5

A plate-type heat exchanger is considered as an intermediate heat exchanger in next-generation nuclear industry. Solid state diffusion welding is a key technology to achieve such high-temperature components with sufficient structural integrity. High-temperature mechanical properties (creep, fatigue, and creep-fatigue) on diffusion weldment have to be provided to regulatory body and/or designers. As a pioneering study, creep deformation and fracture behavior of a diffusion weldment were evaluated in this study. Stress-rupture test was conducted at 800 ℃ under various stress levels. Time-to-rupture, time-to-tertiary stage, and time-to-1% creep strain were measured using an extensometer physically attached to the gauge section of the specimens. Time-to-rupture of the diffusion weldment was comparable to that of the as-received alloy. It was revealed from a plot of log stress versus log time-to-rupture that the underlying creep deformation and fracture mechanism is dislocation glide and climb. All specimens were fractured away from the interface in the gauge section in a ductile manner. Fracture surface and cross section are analyzed with electron microscope.

액상확산접합한 Ni기 단결정 초내열합금의 크리프 파단 및 피로특성

김대업 대한용접접합학회 2001 대한용접·접합학회지 Vol.19 No.1

The creep-rupture and low cycle fatigue properties of transient liquid phase bonded joints of Ni-base single crystal superalloy, CMSX-2 was investigated using MBF-80 insert metal. The (100) orientation of bonded specimen was aligned perpendicular to the joint interface. CMSX-2 was bonded at 1523K for 1.8ks in vacuum, optimum bonding condition. The creep rupture strength and rupture lives of the joints were the almost identical to ones of the base metal. SEM observation of the fracture surfaces of joints after creep rupture test revealed that the fracture surfaces classified three types of region, ductile fracture surface, cleavage fracture surface and interfacial fracture surface. The low cycle fatigue properties of the joints were also the same level as those of base metal. The elongation and reduction of area values of joints were comparable to those of base metal while fell down on creep rupture condition of high temperature.

Creep and creep-rupture of Alloy 617

Wright, J.K.,Lillo, T.M.,Wright, R.N.,Kim, Woo-Gon,Sah, In-Jin,Kim, Eung-Seon,Park, Ji-Yeon,Kim, Min-Hwan Elsevier 2018 Nuclear engineering and design Vol.329 No.-

<P><B>Abstract</B></P> <P>The Ni-Cr-Mo-Co material Alloy 617 is the leading candidate for VHTR intermediate heat exchangers operating above 750°C. Time-dependent properties are an important consideration in qualifying the alloy for construction of nuclear components. Creep behavior of several different heats of Alloy 617 has been evaluated in the temperature range of 800–1000°C. Power law creep behavior was observed for the minimum creep rate, with a stress exponent of 5.6 and activation energy of approximately 400kcal/Mol. The Monkman-Grant approach relating minimum creep rate to time to rupture gave a reasonable representation of the data for all of the testing with a slope of −0.84. Similarly, a modified Monkman-Grant fit the strain to failure data reasonably well. A Larson-Miller analysis was carried out to compare rupture behavior determined in the current experiments and historical data with well-known provenance over a wide range of conditions. It appears that the properties of modern heats of material are near the lower bound of rupture behavior when all of the data are considered in the same analysis.</P>

초 두랄루민(Al 2024)의 정적인 크리프 거동

황경충,윤종호 한국공작기계학회 2004 한국공작기계학회 추계학술대회논문집 Vol.2004 No.-

Super-duralumin has widely been used as the part materials of aerospace and automobile industry because it has high specific strength and also is light. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, every creep test under four constant stress conditions have been conducted for four temperature conditions. A series of creep tests had been performed to get the basic design data and life prediction of super-duralumin products and we have gotten the following results. First, the stress exponents showed the descending trend as the test temperatures increase. Secondly, the creep activation energy gradually decreased as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy was estimated about 6. And last, the fractographs at the creep rupture showed both the brittle fracture due to the transgranular rupture.

다양한 온도에서의 응력 파단 시험 결과 분석을 통한 크리프 수명 예측 방법에 관한 연구

이정민,송현우,윤정한,박수,석창성 대한기계학회 2019 大韓機械學會論文集A Vol.43 No.5

발전시스템의 고효율화가 추진됨에 따라 발전시스템의 가동온도가 높아졌으며, 그에 따라 고온 환경에서 핵심부품의 내구성 확보가 중요시되고 있다. 고온 환경에서 내구성을 확보하기 위하여 초내열합금이 적용되고 있으며, 그중 니켈기 초내열합금이 고온강도, 크리프 및 피로 저항성, 내산화성이 우수하여 터빈 블레이드 소재로 널리 사용되고 있다. 터빈 블레이드는 고온 환경에 노출될 뿐만 아니라 고속회전에 의한 원심력을 받으며, 이로 인하여 크리프 변형이 발생한다. 따라서 블레이드 설계시 크리프 파단 수명이 반드시 고려되어야 한다. 본 연구에서는 상용 가스터빈 블레이드 소재로 사용되는 IN738LC에 대한 크리프 특성을 분석하기 위하여 여러 온도조건에서의 크리프 파단 시험 결과를 확보하였으며, 이로부터 IN738LC의 크리프 수명을 예측하기 위한 방법에 대한 연구를 수행하였다. As the efficiency of power-generation systems has improved, their operating temperature has increased. Accordingly, it is important to secure the durability of the core parts in a high-temperature environment. To ensure this durability, super heat-resistant alloys have been applied. Among them, nickel-based alloys have been widely used as turbine-blade materials because of their high-temperature strength, and creep, fatigue, and oxidation resistance. The turbine blades are not only exposed to high-temperature environments, but also to centrifugal force, due to the high-speed rotation, which causes creep deformation. Therefore, the creep-rupture life must be considered when designing the blade. In this study, the creep rupture was tested at various temperature conditions, and a study on the creep-life prediction method was conducted by analyzing the creep characteristics of the IN738LC superalloy, which is used as a commercial gas-turbine blade material.

EFFECT OF MINOR ELEMENTS ON THE CREEP RESISTANCE OF Mg-Zn-Mn-(Ca) ALLOY

D. M. KANG,J. O. AN,J. S. KWAK 한국자동차공학회 2010 International journal of automotive technology Vol.11 No.6

Along with alumium, titanium and composite alloys, magnesium alloys have been given much attention by industry for applications such as lightweight automobiles and electronics because of their high strength, low specific density and good damping characteristics. In this paper, creep tests were done with magnesium alloys (Mg–3% Zn–1% Mn, Mg–1.2% Zn–1% Mn, and Mg–3% Zn–1% Mn–0.3% Ca) containing different amounts of Zn to investigate the effect of Zn and Ca on the deformation behavior and the rupture time for Mg alloy creep under elevated temperatures. The alloys were obtained as follows: (1) pure magnesium (9.7 kg) was melted at 720oC in an SF6 atmosphere; (2) the temperature was increased up to 800-820oC after adding 0.3 kg of pure Mn to make the Mg–1% Mn master alloy; (3) the minor element (Zn, Ca) was added to the master alloy; and (4) the magnesium alloy melts were cast into a metallic mold preheated to 150oC. The creep tests were executed under a constant load and temperature to measure the steady-state rate and rupture time of creep. Based on the experimental results, the creep behavior of the alloys seemed to be controlled by dislocation climb at around 0.5~0.55Tm (Tm; melting temperature). In addition, the results showed that the addition of Ca was effective for increasing the creep resistance of a Mg alloy: the more Zn present in the alloy, the stronger the creep strength of the alloy

Ultrasonic Evaluation of Creep Damage in 316LN Stainless Steel

Song-Nan Yin,Yeong-Tak Hwang,Won Yi 한국정밀공학회 2007 International Journal of Precision Engineering and Vol.8 No.4

Creep failure of 316LN stainless steel (SS) occurs due to the nucleation and growth of cracks. An investigation was performed to correlate the creep damage with ultrasonic wave speeds and angular frequencies using creep-tested 316LN SS specimens. Ultrasonic wave measurements were made in the direction of and perpendicular to the loading using contact probes with central frequencies of 10. 15. and 20 MHz. We found that the angular frequency and wave speed decreased with increasing creep time to rupture by analyzing the ultrasonic signals from the 15 and 20 MHz probes. Therefore, the creep damage was sensitive to the angular frequency and wave speed of ultrasonic waves.

고온 폐열회수장치 튜브의 크리프 파단특성 평가

김우중 ( Woo Joong Kim ),김재훈 ( Jae Hoon Ki ),장중철 ( Jung Cheol Jang ),김범수 ( Beom Soo Kim ),이기천 ( Gi Chun Lee ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.3

The Heat Recovery Steam Generator (HRSG) is a device recycling the exhaust gas of gas turbine in combined power and chemical plants. Since service temperatures was very high, the damage of HRSG tubes intensively occurred in superheater and reheater. The aim of this paper is to determine life and hardness relationship that addresses creep-rupture test and creep-interrupt test in modified 9Cr-1Mo steel. The measured life that consists of function of hardness was found to constant tendency.

초 두랄루민(Al 2024)의 정적인 크리프 거동

황경충(Kyung-choong Hwang),윤종호(Jong-ho Yoon) 한국생산제조학회 2004 한국생산제조시스템학회 학술발표대회 논문집 Vol.2004 No.10

Super-duralumin has widely been used as the part materials of aerospace and automobile industry because it has high specific strength and also is light. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, every creep test under four constant stress conditions have been conducted for four temperature conditions. A series of creep tests had been performed to get the basic design data and life prediction of super-duralumin products and we have gotten the following results. First, the stress exponents showed the descending trend as the test temperatures increase. Secondly, the creep activation energy gradually decreased as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy was estimated about 6. And last, the fractographs at the creep rupture showed both the brittle fracture due to the transgranular rupture.