Effect of ratchet strain on fatigue and creep-fatigue strength of Mod.9Cr-1Mo steel

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

安藤 勝訓 ; 磯部 展宏*; 菊地 浩一*; 江沼 康弘*

Ando, Masanori; Isobe, Nobuhiro*; 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鋼が繰返し軟化材料であり、累積ひずみを加えても繰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繰返し軟化により相殺され、寿命中期では平均応力がほとんど発生しないためと考えられた。

The effect of ratcheting deformation on fatigue and creep-fatigue life in Mod.9Cr-1Mo steel was investigated. Uniaxial fatigue and creep-fatigue testing with superimposed strain were performed to evaluate the effect of ratcheting deformation on the failure cycle. In the fatigue tests with superimposed strain at 550C, slight reductions of failure lives were observed. All of the numbers of cycles to failure in the fatigue tests with superimposed strain were within a factor of 1.5 of that of the fatigue test without superimposed strain at 550C. The apparent relationship between failure cycles and testing parameters was not observed. It was assumed that suppression of mean stress generation by cyclic softening reduces the effect of ratcheting strain. In the creep-fatigue tests with superimposed strain, test results indicated that the accumulated stain was negligible.