高純度SUS304系合金の照射後SSRT特性へのS, P, C, Ti添加の影響

Effects of S, P, C and Ti addition on slow strain rate tests properties of irradiated high purity type 304 alloys

中野 純一; 根本 義之  ; 沼田 正美; 田口 剛俊 ; 塚田 隆 

Nakano, Junichi; Nemoto, Yoshiyuki; Numata, Masami; Taguchi, Taketoshi; Tsukada, Takashi

照射誘起応力腐食割れ(IASCC)へ及ぼす添加元素の影響を調べるために、高純度SUS304系合金を製造し、微量元素、Si, S, P, C, Tiを添加した。JRR-3を用い、3.510n/m(E1MeV)まで中性子照射を行い、561Kの高温高圧水中で低ひずみ速度引張(SSRT)試験後、破面観察及び硬さ試験を行った。Si及びC添加合金に関しては以前に報告済みである。P添加合金では、他の合金よりも低い約15%の粒界型応力腐食割れ(IGSCC)破面率を示し、P添加によりIASCC感受性が低下したといえる。S添加合金では照射量6.710n/mの場合とほぼ同じIGSCC破面率でありSCC感受性が低照射量で飽和していたと見られる。粒界と粒内で硬さに差はなかったが、Cを含む合金の硬さは、他の合金よりも高い値となり、Cの添加による硬化が顕著に現れた。

To evaluate the effects of minor elements on Irradiated Assisted Stress Corrosion Cracking (IASCC), type 304 stainless steels with high purity were fabricated and minor elements, Si, S, P, C, Ti, were added. After neutron irradiation to 3.510 n/m (E1MeV) in the JRR-3, Slow Strain Rate Tests (SSRT) were performed in oxygenated water at 561 K. Subsequently, fracture surface examination and hardness test were performed. The results of the steels with Si and C have been reported already. The specimen with P showed approximately 15% in Intergranular Stress Corrosion Cracking (IGSCC) fraction which was the lowest in the all specimens. P addition may reduce susceptibility to IASCC. IGSCC fraction of the specimen with S was similar to that of the specimen irradiated to 6.710 n/m. Hardness in the grains was similar to that at grain boundaries. Hardness of the specimens with C was higher than that of the specimens without C.