Influence of Creep and Fatigue Pre-damage on Creep-Crack- and Fatigue-Crack-Growth Rates of CrMoV Rotor Steel
Masaru SEKIHARA and Shigeo SAKURAI
Abstract:The effect of mechanical degradation in a long-term-operated component on the creep- and fatigue- crack growth rates was studied. Creep-crack-growth tests and fatigue-crack growth tests were performed on creep-pre-strained and cyclic-strained CrMoV rotor-steel specimens. It was found that under constant load, creep-crack growth rates, da/dt, of the creep -pre-damaged specimens were higher than those of virgin specimens. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep-void-induced specimens was increased 5times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fall in a narrow scatter band in the relationship between creep J integral C* and da/dt. Another result showed that fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were higher than those of virgin specimens. Under the same stress intensity factor range ĢK, da/dN in an about 10%-crept specimen was increased 20 times. And da/dN in fatigue-pre-damaged specimens were accelerated 10 times. However, the results of the strain-controlled crack growth test fall in a narrow scatter band in the relationship between J integral range ĢJ and da/dN. These results suggest that the creep remaining lives and fatigue remaining lives of the mechanically damaged CrMoV rotor steel can be estimated by using C* & ĢJ of the damaged material and the da/dt and da/dN values of the virgin material. Key Words:CrMoV rotor steel, High temperature, Creep, Fatigue, Crack growth, Degradation, C*, ĢJ