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비선형 초음파를 이용한 주조 오스테나이트 스테인리스강 열취화 손상 평가
이기영,김현명,김진겸,강성식,김종범 한국비파괴검사학회 2023 한국비파괴검사학회지 Vol.43 No.6
가압경수형원자로의 1차 계통의 가동 운전 환경에서 주조 오스테나이트 스테인리스강(Cast austenitic stainless steels, CASS)은 스피노달 분해가 발생하는 온도보다 낮은 온도임에도 불구하고, 가동 운전 환경에서장시간 노출되면서도 심각한 열취화 현상이 발생하고, 이에 따라 파괴인성이 감소하는 등 기계적 특성의 변화가 발생하는 것으로 알려져 있다. 따라서, 주조 스테인리스강의 열취화가 진행됨에 따라 파괴인성과 관련된 재료 물성 변화를 평가하기 위해 비선형 초음파 기법을 적용하였다. 이를 위해, 다양한 온도와 시간으로열처리한 2종류의 주조 오스테나이트 스테인리스강(CF8과 CF8M)을 준비하였고, 이 재료에 대하여 열취화에따른 초음파 비선형 파라미터와 강도의 변화 사이의 상관관계를 분석하였다. In the operational conditions of the primary system of a pressurized water reactor, cast austenitic stainless steels (CASS) experience pronounced thermal embrittlement, persisting even during prolonged exposure to the operational environment at temperatures below the threshold for spinodal decomposition. This phenomenon is recognized for inducing alterations in mechanical properties, notably a reduction in fracture toughness. Consequently, we employed nonlinear ultrasonic techniques to assess shifts in material properties associated with the progression of heat embrittlement in cast stainless steel. To facilitate this investigation, two variants of cast austenitic stainless steels (CF8 and CF8M) were heat-treated at various temperatures and durations. Subsequently, we conducted an analysis to establish correlations between ultrasonic nonlinear parameters and the changes in strength attributable to heat embrittlement.
인공신경망을 이용한 주조 스테인리스강의 열취화 민감도 평가
김철,박흥배,진태은,정일석,Kim, Cheol,Park, Heung-Bae,Jin, Tae-Eun,Jeong, Ill-Seok 대한기계학회 2004 大韓機械學會論文集A Vol.28 No.4
Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained teaming data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.
원전배관용 주조 스테인리스강의 열화에 의한 2축 피로수명 예측
박중철(Joong Cheul Park),권재도(Jae Do Kwon),류근준(Geun Jun Lyu),권정락(Jeong Rock Kwon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
The multiaxial fatigue test under in-phase and out-of-phase load were performed to study what degradation phenomenon affects fatigue life with virgin and 3600 hrs degraded materials. The various kind of fatigue data for fatigue life prediction were acquired under pure axial and pure torsional load of fully reversal condition. The models which was investigated are: 1) the von Mises equivalent strain range, 2) the critical shear plane approach method of Fatemi-Socie(FS) parameter, 3) the modified Smith-Watson-Topper(SWT) parameter. The result showed that, fatigue life by material degradation are decreased and life prediction which was used the FS parameter is not conservative but the best result.
열취화에 의한 원전배관용 주조스테인리스강의 기계적 특성변화비교
조선영(Sun Young Cho),장창희(Changheui Jang),정일석(Ill Seok Jeong),이승건(Seong Gun Lee),박흥배(Heung Bae Park),진태은(Tae Eun Jin) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
Cast duplex stainless steels like CF8M and CF8A for primary piping in pressurized water reactors are susceptible to embrittlement by thermal aging in service. They exhibit a two-phase structure made up of δ-ferrite in austenite matrix. Spinodal decomposition and precipitation of G-phase are known to be responsible for strengthening of the ferrite phase after aging. Thermal aging embrittlement is mainly characterized by δ-ferrite contents and the evolution of Charpy impact property and fracture toughness. The objective of this paper is to summarize the method of estimating δ-ferrite contents, Charpy impact energy and J-R curve and to evaluate the thermal embrittlement of the cast stainless steel pipings used in the domestic nuclear power plants. Also, the applicability of the estimation methods is checked using the reported test results.
자동압입과 EDS를 이용한 주조 스테인리스강의 열화특성 평가
백승(Seung Baek),이영민(Young-Min Lee),석창성(Chang-Sung Seok),김철(Cheol Kim),진태은(Tae-Eun Jin),정일석(Ill-Seok Jeong) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
Cast austenitic stainless steel piping and pump, valve casings, elbows are susceptible to reduction in toughness and ductility because of long term exposure LWR(light water reactor) operating temperatures. In this paper, we have measured the material properties of long-term aged CF-8A cast stainless steel, accelerated aging at 400℃. These studies have been carried out to using ABI(automated ball indentation) test and EDS(energy dispersive spectroscopy). The fracture toughness of CF-8A cast stainless steel was also determined by using standard fracture toughness and Charpy tests. The decrease in fracture toughness on accelerated aging for 3,572 hours more than 38% compared to the unaged values.
산소가 제거된 310 ℃ 순수환경에서 CF8M 주조 스테인리스강의 환경 피로거동ㆍ수소 및 미세구조의 영향
장훈(Hun Jang),조평연(Pyungyeon Cho),장창희(Changheui Jang),김태순(Tae Soon Kim) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.1
CF8M (11% ferrite) 주조 스테인리스강의 310 ℃ 순수환경에서의 저주기피로 수명에 미치는 수소 및 미세구조의 영향을 분석하였다. CF8M 의 경우, 공기환경 대비 310 ℃ 순수환경에서의 피로수명의 감소는 단조재인 316LN 에 비해 다소 작았다. 미세구조 및 파면 분석을 통해, CF8M 의 저주기피로 수명의 감소는 316LN 의 경우와 마찬가지로 수소유기균열에 의한 것으로 판단되었다. 그러나, CF8M 의 경우, 페라이트상 경계에 수소유기균열에 의한 2 차 균열이 빈번히 발생함에 따라 균열 선단에서의 응력집중이 저하되는 효과가 있었다. 이러한 응력집중의 완화로 인해 수소유기균열에 의한 피로균열진전이 둔화 되어 결과적으로 저주기피로 수명의 저하가 완화되는 것으로 판단되었다. The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a 310 ℃ deoxygenated water environment. The reduction of LCF life of CF8M in a 310 ℃ deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a 310 ℃ deoxygenated water.
변형률속도가 CF8M CASS 환경피로 수명에 미치는 영향 평가
정일석(Ill-Seok Jeong),하각현(Gak-Hyun Ha),전현익(Hyun-Ik Jeon) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
The Environmental fatigue life of CF8M cast stainless steel is influenced by mechanical, environmental and metallurgical parameters, such as strain rate, strain amplitude, temperature, dissolved oxygen concentration, water flow rate and so on. In an actual plant, the mechanical and environmental parameters are changing during the plant operation. Therefore, the effect of such mechanical and environmental parameter changes on fatigue life evaluation have to be studied. Low cycle fatigue life of structural materials diminishes remarkably as functions of various parameters in high temperature and high pressure environments. Such reduction can be estimated by the fatigue life reduction factor(Fen). In this study, fatigue tests were performed under changing conditions of strain amplitude, strain rate. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitudes at 0.004 %/s strain rate, and the fatigue life correction factor was evaluated according to the equation modified by U. S. Nuclear Regulatory Commission(U.S.NRC) and Japanese Environmental Fatigue Tests committee(JEFT).
주조 스테인리스강 CF8M의 43$0^{\circ}C$ 열화거동에 관한 연구 (III) - 탄소성 파괴인성 평가 -
권재도,인재현,박중철,최성종,박윤원,Gwon, Jae-Do,In, Jae-Hyeon,Park, Jung-Cheol,Choe, Seong-Jong,Park, Yun-Won 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.10
A cast stainless steel may experience an embrittlement when it is exposed to approximately 30$0^{\circ}C$ for long period. In the present investigation, The three classes of the thermally aged CF8M specimie n are prepared using an artificially accelerated aging method. Namely, after the specimen are held for 300, 1800 and 3600hrs. at 43$0^{\circ}C$ respectively, the specimens are quenched in water to room temperature. Load versus load line displacement curves and J-R curves are obtained using the unloading compliance method. $J_{IC}$ values are obtained following ASTM E 813-87 and ASTM E 813-81 methods. In addition to these methods, JIC values are obtained using SZW(stretch zone width) method described in JSME S 001-1981. The results of the unloading compliance method are $J_Q$=485.7 kJ/m$^2$ for virgin material, $J_{IC}$ of the degraded materials associated with 300, 1800 and 3600hrs are obtained 369.25 kJ/m$^2$, 311.02 kJ/m$^2$, 276.7 kJ/m$^2$, respectively. The results of SZW method are similar to those of the unloading compliance method. Through the elastic-plastic fracture toughness test, it is found that the value of $J_{IC}$ is decreased with increasing of the aging time. The results obtained through the investigation can provide reference data for a leak before break(LBB) of reactor coolant system of nuclear power plants.