電気化学的非破壊検出法を用いたクリープ疲労累積損傷の評価法に関する研究

Evaluation of creep-fatigue damage accumulation by means of electrochemical nondestructive detection method

庄子 哲雄*; 渡辺 豊*; 駒崎 慎一*; 川原 鉄士*

not registered; not registered; not registered; not registered

本研究では,高速炉構造用316FR鋼についてクリープ疲労損傷の非破壊検出法の開発を目的として,電気化学的手法,集中誘導型交流電位差法(ICFPD)による検討を行った。キャビティの優先的形成箇所となる粒界析出物の定量的検出を目的とし,電気化学的手法の適用性を検討した。1N KOHおよび1N H2SO4+KSCN溶液の2種類の検出電解液を用いたアノード分極曲線の計測を行った。1N KOHにおいて,粒界析出物の選択的溶解に対応するピーク電流が観察され,粒界析出物の析出量という側面からクリープ疲労損傷を検出できる見通しが得られた。また,粒界析出に伴うCr欠乏層の形成に着目した1N H2SO4+KSCN溶液を用いたアノード分極の結果から,損傷度と再活性化率とを対応づけられることが示された。集中誘導型交流電位差法(ICFPD)を用いたクリープ疲労損傷材の計測では,新材と損傷材の間に明確な差が認められた。詳細な検討は今後の課題であるが,電位差信号は,キャビティ,析出物,表面き裂等のクリープ疲労における微視的損傷因子を反映しているものと期待され,電位差の連続モニタリングによるクリープ疲労損傷検出の見通しが得られた。

In this study, for the purpose of development of a nondestructive detection technique of creep-fatigue damage in Type 316FR stainless steel for fast reactors, application study of electrochemical methods and the Induced Current Potential Drop(ICFPD) was done. Applicability of electrochemical methods to evaluation of grain boundary precipitates which, provide preferred site for cavities was investigated. Anodic polarization curves were measured both in 1N KOH solution and in 1N HSO+KSCN solution. An anodic current peak that, corresponds to preferential dissolution of the grain boundary precipitates was observed in the measurements using in the KOH solutlon. It was suggested that evolution of the grain boundary precipitates which should be associated with creep-fatigue damage can be evaluated by the electrochemical method using KOH solution. The results of reactivation ratio of the material in 1N HSO+KSCN solution, which is recognized as the sensitive indicator of Cr-depletion, suggested a correlation between the reactivation ratio and creep-fatigue damage. Clear differences between the as-received material and the creep-fatigue damaged sample were found in ICFPD results. Although more detailed investigation is required to make a conclusion, it was expected that potential drop can reflect creep-fatigue damage in the microstructure, e.g. precipitates cavities, surface cracks. Based on the preliminaly result, the ICFPD technique may be expected to provide a quantitative monitoring capability of creep-fatigue damage.