Abstract
Creep crack growth behavior was experimentally investigated at 570°C in 2 1/4Cr-1Mo cast steels, taken out of heavy section components in power boiler plants of which the total service life were longer than 100000 hours. Stress intensity factor, load line displacement rate, C* -integral andQ* -parameter were used as parameters to evaluate the creep crack growth rate. And, degradation of crack growth in aged materials was observed in the evaluations.
In the relationship ofC* -integral or load line displacement rate, and the creep crack growth rate, the so-called tail part, which characterizes the early stage of the test owing to the transient behavior, was considered. The relationship between the minimum of load line displacement rate and fracture life fell on practically a single trend line in terms of Monkman-Grant type equation. It means that the equation is found to be of activation type.
At last, the softening region near crack tip was discussed in the relation of the crack growth resistance.
