抄録
In order to investigate the characteristics of creep-fatigue interaction and its mechanism for Cr-Mo-V steel forgings, the creep-fatigue tests were carried out under a strain-controlled condition for long-term and the metallographic observations were conducted on the interrupted creep-fatigue specimens.
The results obtained are summarized as follows:
(1) The data obtained were evaluated using the linear life fraction damage rule. The value of creep damage (Dc) was lower than the value of fatigue damage (Df) by two orders of magnitude for the tests conducted. Consequently, Dc+Df≅Df. The fracture mode was transgranular as is generally seen in the fatigue dominant fracture. However, fracture occurred at a small value of Df when the hold time was added.
(2) Metallographic observation, however, showed that creep cavities nucleated and grew inside the specimen with increasing number of cycles in the case of long hold time and low strain-range. Moreover, it was found that fatigue micro-cracks of the case where creep cavities and creep cracks were observed in the fractured specimen had a tendency to propagate and link up along grain boundary.
(3) It is suggested from the above mentioned results that, even though Dc is very small, creep cavities and creep cracks nucleate, and that they reduce the fatigue life by the effect of their linkage with fatigue crack.
