改良9Cr-1Mo鋼の疲労寿命及びクリープ疲労寿命に及ぼす予ひずみ及び進行性ひずみの影響

Effect of pre-strain and ratcheting strain on fatigue and creep-fatigue lives in Mod.9Cr-1Mo steel

安藤 勝訓 ; 磯部 展宏*; 伊達 新吾*; 菊地 浩一*; 江沼 康弘*

Ando, Masanori; Isobe, Nobuhiro*; Date, Shingo*; Kikuchi, Koichi*; Enuma, Yasuhiro*

改良9Cr-1Mo鋼について、累積ひずみが疲労及びクリープ疲労寿命に与える影響について調査するため、ラチェット疲労及びラチェットクリープ疲労試験を実施した。種々の試験パラメータと寿命の関係について検討したが、一連の試験の範囲では疲労及びクリープ疲労寿命ともに累積ひずみの影響は確認できなかった。これは改良9Cr-1Mo鋼が繰り返し軟化材料であり、累積ひずみを加えても繰り返し負荷中の平均応力が発生しない、もしくは発生しても軟化挙動により相殺され寿命中期では、平均寿命がほとんど発生しないためと考えられた。

The effect of ratcheting deformation and pre-strain on fatigue and creep-fatigue life in Mod.9Cr-1Mo steel was investigated. Uni-axial fatigue and creep-fatigue tests with pre-strain and progressive strain were performed to evaluate the effect of pre-strain and ratcheting strain on the failure cycle. In the fatigue tests with pre-strain, failure lives were not declined. In the fatigue tests with progressive strain, slight reductions of failure lives were observed, however, they were within a factor of 1.5 of the failure life in normal fatigue test. In the creep-fatigue tests with progressive strain, the same conclusion of the fatigue tests was obtained. In both kinds of tests, maximum mean stresses during the tests were insignificant and/or generated in early cycle in the tests, and this character is considered as a reason of that the effect of ratcheting deformation on the fatigue and creep-fatigue lives are insignificant.