Study on effect of microstructure on crack propagation behavior in austenitic stainless steels

き裂進展に及ぼす材料微細組織の影響評価に関する研究

加治 芳行  ; 近藤 啓悦  

Kaji, Yoshiyuki; Kondo, Keietsu

オーステナイト系ステンレス鋼のき裂進展挙動に及ぼす照射速度の影響を調べるため、JMTRにおいて1E-81E-7dpa/sの照射速度範囲で照射したオーステナイト系ステンレス鋼(はじき出し損傷量約1dpa)を用いて高温水中のき裂進展試験を実施し、さらに進展き裂周辺のミクロ組織観察をEBSD法により実施した。き裂進展速度(CGR)に関しては、高照射速度材の方が若干高いCGRを示すものの、進展き裂周辺の平均塑性ひずみ量をgrain orientation spread (GOS)を使って評価するとひずみ量は約1%程度であり、照射速度による違いは見られなかった。さらに、照射量が約2倍である照射材のき裂周辺の塑性ひずみ量の評価等を行い、き裂進展挙動に及ぼす照射速度の影響について議論する。

In order to investigate the influence of neutron dose rate on crack propagation behavior of type 304 stainless steel, crystallographic analyses around the cracks were conducted by Electron Backscattered Diffraction (EBSD) on crack growth rate (CGR) tested specimens irradiated at the Japan Materials Testing Reactor (JMTR) up to about 1dpa under the dose rate conditions from 1E-8 to 1E-7 dpa/s. Although CGRs of specimens with different dose rates suggested that specimens with the higher dose rate irradiation showed the slightly larger CGR than that with lower dose rate irradiation, estimation of the plastic strain by means of the EBSD measurement revealed that plastic strain around the crack in both low and high dose rate specimens was estimated to approximately 1%, and the significant difference was not observed. Furthermore, the distribution of plastic deformation around the crack is estimated on the specimens irradiated up to about 2 dpa and the influence of neutron dose rate on crack propagation behavior is discussed in this study.