本研究では、PWRプラント運転を想定した熱時効初期の残留応力緩和メカニズム解明の一環として、LP、WJP、バフ研磨の三工法および機械加工を施した600合金について、熱時効時の組織変化を明確にすることを目的とした。各工法の施工材についてEBSD解析を行うことにより、応力緩和過程に関与すると考えられる組織学的因子の検討を実施した。...
英字タイトル:
Microstructural Investigation of Residual Stress Relaxation Process of Ni-based Alloy by EBSD Analysis

The relaxation behavior of the compressive stress in nickel-based alloy 600 introduced by WJP and buffing stress improving treatments has been investigated. Hardness reduction behavior in WJP and buffing processed samples during thermal aging has been found to follow the Johnson-Mehl-Avrami equation and the rate constant for hardness reduction to be expressed by the Arrhenius equation. EBSD crystal orientation analysis has confirmed that the strain is introduced mainly in the surface region. Positron lifeti...
英字タイトル:
Mechanism for stress relaxation behavior of WJP and buffing stress improving treatments

In order to prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). However, the compressive residual stresses induced by WJP might be relaxed during the actual operation because of the elevated temperature environment. Therefore, the stability of the compressive residual stresses caused by WJP has been investigated during thermal aging. The result shows that the compressive residual stresses has...
英字タイトル:
Relaxation behavior of residual stress generated by water jet peening under operation temperature environment ― Evaluation for long term stability of residual stress improving treatment on Ni base alloy (report 1) ―

Abstract The fusion reactor is expected as a next-generation electric source to resolve electricity shortage. The reduce d activation steel F82H has been considering as the structural material for blanket modules set in fusion reactors. In t he case of welding for the steel, its demanded to minimize the heat affected zone (HAZ). Therefore, laser beam welding ( LBW) has been considering as one of welding methods to construct the modules. The objectives of this investigation are t o clarify the critical cond...
英字タイトル:
Study on Applicability of Laser Beam Welding for Reduced Activation Ferritic Steel F82H

Fiber laser welding is expected to be especially useful for the fabrication of ITER test blanket module for fusion reactor components. The objective of this study is to clarify the weldabilit y of the dissimilar butt joint between F82H and SUS316L. The plates 4 mm thick of F82H and SUS31 6L were butt-welded by 4 kW fiber laser welding. In 0.2 mm amount of shift from the abutting su rface to SUS316L side, the weld metal region had a mixed phase where the austenite and the ferri te coexist after welding. Vic...
英字タイトル:
Fiber Laser Welding for Dissimilar Butt Joint of Reduced Activation Ferritic Steel / Austenite Stainless Steel

Stress corrosion cracking (SCC) is one of serious aging degradation problems for the Alloy 600 components of pressurized water reactors (PWRs). In order to prevent SCC, various methods such as water jet peening (WJP), laser peening (LP), surface polishing have been used to introduce compressive stresses at the surfaces of the PWR components. However, it has been reported that such compressive residual stress introduced by these methods might be relaxed during the practical operation, because of high te...
英字タイトル:
Kinetic analysis on the long term stability of the effect obtained by various residual stress improvement methods ― Evaluation for long term stability of residual stress improving treatment on Ni base alloy (report 2) ―

In order to estimate the stability of the stress improving effect by water jet peening (WJP) residual stress improvement methods during the long-term operation of nuclear power plants, the residual stress in nickel-based alloy 600 has been studied through the kinetics of hardness reduction behavior in practical operation temperatures. Based on the relationship between the residual stress relaxation and the hardness reduction rates, it has been found that in actual operating condition, when the hardness decr...
英字タイトル:
Prediction of Residual Stress Stability Introduced by Water Jet Peening Residual Stress Improvement Method to Ni-based Alloy during Long-Term Operation

In order to compare the stability of the stress improvement effect introduced by laser peening (LP), water jet peening (WJP) and buffing residual stress improvement methods during the long-term operation of nuclear power plants, the hardness in nickel-based alloy 600 has been studied through the kinetics of hardness reduction behavior in practical operation temperatures. The predicted hardness results show that in actual operating condition, the time required to reduce the hardness to 180HV is 1268 years fo...
英字タイトル:
Long-Term Stability Comparison of LP, WJP and Buffing Residual Stress Improvement Methods under Actual Operating Condition

Abstract Surface finishing methods, such as Water Jet Peening (WJP), have been applied to welds in some major components of nuclear power plants as a counter measure to Primary Water Stress Corrosion Cracking (PWSCC). In addition, the methods of surface finishing (buffing treatment) is being standardized, and thus the buffing treatment has been also recognized as the well-established method of improving stress. On the other hand, the long-term stability of peening techniques has been confirmed by acc...
英字タイトル:
Prediction method of long-term reliability in improving residual stresses by means of surface finishing

原子力発電プラントの高経年化に伴い発生する経年劣化事象の一つである応力腐食割れ(Stress Corrosion Cracking: SCC)の防止対策として、溶接に伴って発生した引張残留応力を圧縮残留応力に変化させる応力改善が有効である。 本研究では、材料内部の格子欠陥の存在状態を定量的に、かつ、高感度に評価できる陽電子寿命法を採用することにより、応力改善工法の施工により導入された残留応力に密接に関連する格子欠陥や転位によるひずみの存在を調査した。...
英字タイトル:
Consideration on Mechanism of Residual Stress Relaxation Behavior of Ni-based Alloy Using Positron Annihilation Lifetime Spectroscopy?