Electrochemical Study on Localized Corrosion of Laser Surface Melted Alloy 600

Lim, Yun Soo,Hur, Do Haeng,Kim, Hong Pyo,Kim, Joung Soo,Kwon, Hyuk Sang 한국부식방식학회 2002 Corrosion Science and Technology Vol.31 No.6

The effects of laser surface melting (LSM) on the resistance to localized corrosion such as intergranular stress corrosion cracking (IGSCC) and pitting of Ni-base Alloy 600 were investigated by electrochemical methods. The degree of sensitization ofthe laser heated Alloy 600 measured using the double loop electrochemical potentiokinetic reactivation method in a 0.1 M Na₂S₄O_6 + 20 ppm KSCN solution was considerably low, which demonstrates that the resistance to IGSCC of Alloy 600 in sulfur bearing environments was improved by LSM. The pitting potentials of Alloy 600 in 1 M NaCl at pH 4 and 9 were also markedly increased by the LSM process, compared with that of the non-laser treated Alloy 600. From the microscopic examination, it was found that pitting was initiated around sulfides associated TiN in the matrix of Alloy 600. Homogeneous microstructure associated with the reduction of inclusion size during LSM could be attributed to the increase of resistance to pitting corrosion in the LSM Alloy 600. On the other hand, complete dissolution of pre-existing intergranular Cr-rich carbides and the resultant Cr healing around grain boundaries was responsible for the improvement of IGSCC properties. The resistance to localized corrosion of the laser treated Alloy 600 was discussed from the results of the electrochemical test and microscopic examination.

600합금의 미세조직 변화 및 SCC거동에 미치는 Ce 첨가의 영향

권오철,이용선,임연수,정만교,김정수 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.1

High purity model alloys with major composition Ni-15Cr-9Fe-0.03C (600CEO) and Ni-15Cr-9Fe-0.03C-0.04Ce (600CE4) were produced. Using these model alloys the effect of alloying element Ce on the SCC behavior of Alloy 600 was evaluated in a caustic solution. To obtain carbides precipitated on grain boundaries, the thermal treatment was performed on both the solution annealed model alloys. Microstructural examinations using SEM and TEM EDX showed that the same structural carbides, Cr_(7)Cc₃, were precipitated on both the alloys and no significant difference in the amount of Cr depletion along grain boundaries was observed between the two model alloys. However, it was shown that the coverage of grain boundary carbides was higher in the Ce-bearing alloy (600CE4). The SCC susceptibility of the alloys was investigated in 40%NaOH solution at 315℃. Being evaluated in terms of the maximum crack depth, the SCC susceptibility of the alloy turned out to be reduced by the addition of Ce. The increased resistance to the SCC in the alloy 600CE4 was considered to be attributable to the increased coverage of grain boundary carbides. (Received September 30, 2004)

Crack growth and cracking behavior of Alloy 600/182 and Alloy 690/152 welds in simulated PWR primary water

임연수,김동진,김성우,김홍표 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.1

The crack growth responses of as-received and as-welded Alloy 600/182 and Alloy 690/152 welds toconstant loading were measured by a direct current potential drop method using compact tensionspecimens in primary water at 325 C simulating the normal operating conditions of a nuclear powerplant. The as-received Alloy 600 showed crack growth rates (CGRs) between 9.6 10 9 mm/s and3.8 10 8 mm/s, and the as-welded Alloy 182 had CGRs between 7.9 10 8 mm/s and 7.5 10 7 mm/swithin the range of the applied loadings. These results indicate that Alloys 600 and 182 are susceptible tocracking. The average CGR of the as-welded Alloy 152 was found to be 2.8 10 9 mm/s. Therefore, Alloy152 was proven to be highly resistant to cracking. The as-received Alloy 690 showed no crack growtheven with an inhomogeneous banded microstructure. The cracking mode of Alloys 600 and 182 was anintergranular cracking; however, Alloy 152 was revealed to have a mixed (intergranular þ transgranular)cracking mode. It appears that the Cr concentration and the microstructural features significantly affectthe cracking resistance and the cracking behavior of Ni-base alloys in PWR primary water

저온 풀림 처리 Alloy 600이 1차수 응력 부식 균열에 가장 예민한 이유

김성수,정종엽,김영석 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.12

It has been proposed that a primary water stress corrosion cracking (PWSCC) in pressurized water reactor (PWR) is governed by a lattice contraction due to a short range ordering reaction in Alloy 600. This leads researcher to think that the kinetics of lattice contraction may control a susceptibility of PWSCC in Alloy 600. A lattice variation with ordering treatment at 400 oC was systematically investigated using high resolution neutron diffraction(HRPD) in high temperature mill anneal (HTMA), low temperature mill anneal (LTMA), and sensitized (SEN) Alloy 600. The results showed that ordering treatment caused an isotropic lattice contraction due to short range ordering (SRO) reaction. The lattice contractions of (111) plane are saturated to be 0.04% in 4 to 1500 hours at 400 oC according to prior treatment condition. The lattice contraction in the magnitude of 0.03% of (111) plane in LTMA Alloy 600 is faster by 8 times and 66 times than that of SEN and HTMA, respectively. This fact may explain why the LTMA is most susceptible to PWSCC through of kinetics of lattice contraction in Alloy 600. Thus, it is possible to conclude that the susceptibility of Alloy 600 to PWSCC is governed by the kinetics of (111) lattice contraction.

Alloy 600에서 원자 규칙화에 따른 격자의 수축 거동

김성수 ( Sung Soo Kim ),김대환 ( Dae Whan Kim ),김영석 ( Young Suk Kim ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.12

A lattice variation with ordering treatment at 400 ℃ in Alloy 600 was systematically investigated using neutron diffraction. Alloy 600 was water-quenched, air-cooled, and furnace-cooled from solution anneal- ing treatment at 1095 ℃. These were ordering-treated up to 5,500 hours at 400 ℃. The results showed that the magnitude of lattice contraction depended on the cooling rate and decreased with the cooling rate. This is due to the fact that the number of ordering bonds increases with decrease in cooling rate. The lattice contraction appeared to be anisotropic according to the crystallographic planes. The water quenched specimen showed a maximum lattice contraction up to 0.04% in the {111} and {200} planes, and this was saturated after 2,000 hours. The lattice contraction due to the ordering reaction should be considered in the assessment of integrity in components made of Alloy 600, because the ordering reaction is a spontaneous and unavoidable phenomenon below 520 ℃ in the Alloy 600.

원전 1차측 수화학 환경에서 수소 농도가 Alloy 600의 표면산화 거동에 미치는 영향

임연수,김동진,김성우,황성식,김홍표,조성환 한국부식방식학회 2022 Corrosion Science and Technology Vol.21 No.6

Surface oxides and intergranular (IG) oxidation phenomena in Alloy 600 depending on hydrogen concentration were characterized to obtain clear insight into the primary water stress corrosion cracking (PWSCC) behavior upon exposure to pressurized water reactor primary water. When hydrogen concentration was between 5 and 30 cm3 H2/kg H2O, NiFe2O4 and NiO type oxides were found on the surface. NiO type oxides were found inside the oxidized grain boundary when hydrogen concentration was 5 cm3 H2/kg H2O. However, only NiFe2O4 spinel on the surface and Ni enrichment were observed when hydrogen concentration was 30 cm3 H2/kg H2O. These results indicate that the oxidation/reduction reaction of Ni in Alloy 600 depending on hydrogen concentration can considerably affect surface oxidation behavior. It appears that the formation of NiO type oxides in a Ni oxidation state and Ni enrichment in a Ni reduction (or metallic) state are common in primary water. It is believed that the above different oxidation/reduction reactions of Ni in Alloy 600 depending on hydrogen concentration can also significantly affect the resistance to PWSCC of Alloy 600.

Alloy 600에서의 규칙 불규칙 반응

김성수 ( Sung Soo Kim ),김정수 ( Joung Soo Kim ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.7

It is proved that there exists an ordering reaction in alloy 600. The differential scanning calorimetric (DSC) tests were carried out for the alloy 600 and a Ni2Cr alloy from room temperature to 800℃ Both an exothermic and an endothermic reaction are interpreted in a aspect of order-disorder reaction in the Ni-Cr and the Ni-Fe binary system. The exothermic reaction was observed only in the water quenched specimens from above 600℃ and the cold worked specimens. However, the endothermic reactions were observed at 490-560℃ in all specimens. Especially, a convex endothermic reaction was observed at about 500-620℃ for specimens aged at 474℃ for 1,100 and 10,000 h. In addition, the activation energy for an exothermic reaction in a quenched specimen after a 1095℃-0.5 hr treatment was Q = 190 kJ/mol (~2 eV/atom), which suggests that this reaction is related to a substitutional diffusion process.

Inconel 600 합금의 고온 프레팅 피로수명에 관한 연구

박대규(D. K. Park),우승완(S. W. Woo),윤동환(D. H. Yoon),정한규(H. K. Jeung),정일섭(I. S. Chung),권재도(J. D. Kwon) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The safety needs in the operation of nuclear power plant facilities have been increased due to the high temperature and pressure operation conditions within these facilities. Several reports exist on the fretting occurring in the materials of stearn generator tubes used in nuclear power plants, which leads to a lower service life. The Inconel 600 alloy, used in steam generator tubes, is a type of nickel-chromium based heat resistant alloy. However, it is necessary to establish a systematic database to guarantee its integrity because there are few data indicating fretting fatigue behaviors at both room and high temperature conditions for the Inconel 600 alloy. Thus, this study analyzed the change in the fatigue characteristics of the Inconel 600 alloy under fretting fatigue by applying plain and fretting fatigue tests at 320℃, which is the room and actual operating temperature applied to the materials of stearn generator tubes. In addition, this study measured the change in the friction force for repetitive cycles in fretting fatigue tests and analyzed the mechanism of fretting fatigue by observing the fracture surfaces.

Alloy 600TT 증기발생기 전열관내 일렬 원주방향 표면 일차수응력 부식균열 성장에 미치는 균열 간격의 영향 고찰

허은주(Eun-Ju Heo),김종성(Jong-Sung Kim),전준영(Jun-Young Jeon),김윤재(Yun-Jae Kim) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.3

일차수응력부식균열 개시 모델과 거시적 현상학적인 손상역학 접근론에 기반한 유한요소 손상해석을 수행하여 Alloy 600TT 로 제작된 원전 증기발생기 전열관에 발생하는 일렬 원주방향 표면 일차수응력부식균열의 성장에 미치는 균열 간격의 영향을 고찰하였다. 기존 연구 결과와의 비교를 통해 손상해석 방법의 타당성을 검증하였다. 검증된 방법을 일렬 원주방향 표면 일차수응력부식균열에 적용하였다. 적용한 결과, 단일 균열에 비하여 일렬 균열의 경우 보다 빠른 합체시간과 관통시간을 보이며 균열 간격이 증가할수록 합체시간과 관통시간은 증가함을 확인하였다. 또한 일정 간격이상으로 두 균열이 떨어지면 합체 이전에 관통될 수 있음을 확인하였다. The study investigated the effect of the distance between two collinear circumferential surface cracks on the primary stress corrosion crack (PWSCC) growth in alloy 600TT steam generator tubes using a finite element damage analysis based on the PWSCC initiation model and macroscopic phenomenological damage mechanics approach. The damage analysis method was verified by comparing the results to the previous study results. The verified method was applied to collinear circumferential surface PWSCCs. As a result, it was found that the collinear cracks showed earlier coalescence and penetration times than the a single crack, and the times increased with the distance. In addition, it is expected that penetration may occur before coalescence of two cracks if they are more than a specific distance apart.

Effect of the Amplitude in Ultrasonic Nano-crystalline Surface Modification on the Corrosion Properties of Alloy 600

김영식,김기태 한국부식방식학회 2019 Corrosion Science and Technology Vol.18 No.5

Surface modification techniques are known to improve SCC by adding large compressive residual stressesto metal surfaces. This surface modification technology is attracting attention because it is an economicaland practical technology compared to the maintenance method of existing nuclear power plants. Surfacemodification techniques include laser, water jet and ultrasonic peening, pinning and ultrasonic Nano-crystalsurface modification (UNSM). The focus of this study was on the effect of ultrasonic amplitude in UNSMtreatment on the corrosion properties of Alloy 600. A microstructure analysis was conducted using an opticalmicroscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). Acyclic polarization test and AC-impedance measurement were both used to analyze the corrosion properties. UNSM treatment influences the corrosion resistance of Alloy 600 depending on its amplitude. Below thecritical amplitude value, the pitting corrosion properties are improved by grain refinement and compressiveresidual stress, but above the critical amplitude value, crevices are formed by the formation of overlappedwaves. These crevices act as corrosion initiators, reducing pitting corrosion resistance.