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Vol.13 No.2previousAA177-AA178
Academic Articles
Regular Paper Vol.13 No.2 (2022) p.1 - p.13
 

Long-term stability mechanism for the effect with WJP and buffing residual stress improving treatments

 

Lina YU1 , Kazuyoshi SAIDA1 , Kazutoshi NISHIMOTO1 , Hideki　ARAKI1 , Kazuki　SUGITA1 , Masataka　MIZUNO1 and Naoki CHIGUSA2

 
1Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
2The Kansai Electric Power Co., Inc., 8 Yokota, 13 Goichi, Mihama-cho, Mikata-gun, Fukui 919-1141, Japan
 
Abstract
The mechanism for long-term stability of the compressive stress in nickel-based alloy 600 components of the pressurized water reactor (PWR) plants introduced by water jet peening (WJP) and buffing stress improving treatments has been investigated in the present study. After thermal aging at the maximum actual operating temperature in PWR plants of 340 ℃ for 50 h, considerable hardness reduction was observed in WJP and buffing treated samples, but it was still much higher than that in solution heat-treated (ST) sample. However, after thermal aging at the higher temperature of 700 ℃ for 120 h, which should cause complete recrystallization, the hardness not only in the WJP treated sample but also in the buffing treated sample decreased to the level nearly equal to that of the ST sample. Furthermore, positron lifetime analysis has revealed that vacancies introduced by WJP and buffing treatments were mostly annihilated after thermal aging at the actual operating temperature, however considerable part of dislocations still stably remained. Based on these results, it has been elucidated that the long-term stability of the compressive residual stress in PWR components introduced by WJP and buffing stress improvement treatment can be attributed to the remained dislocations of relatively stable situation in the actual operating condition of PWR plants.
 
Keywords
Long-term stability, WJP, Buffing, Hardness, Positron lifetime
 
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Article Information
Article history:
Received 10 May 2021
Accepted 17 November 2021