Inelastic Deformation and Crack Growth Behavior of CrMoV Cast Steel after Long-Term Service at High Temperature

Abstract

For the purpose of residual life prediction of high-temperature components after long-term service, both stress-strain behavior for evaluating fracture mechanics parameters and crack growth behavior were examined using CrMoV cast steel taken from a main steam valve served for 155,000 hours at 811K under 216 start-stop cycles. Firstly the influence of cyclic softening and thermal aging history on the stress-strain curve was examined. As a result of comparison between virgin and long-term served material, a possibility of predicting the stress-strain behavior of the long-term-served material from that of virgin material was discussed. Secondly creep and fatigue crack growth behavior of long-term served material were experimented and compared with those of virgin material. Finally creep-fatigue crack growth tests under displacement-controlled condition were carried out with structural model specimens made of the long-term served material. The crack growth behavior of the tests was simulated using the method proposed by the authors on the basis of the monotonic stress strain curve and the stress strain curve of half-fatigue life of the material. Comparison with the test results showed that the simulation using the monotonic stress-strain curve of the material gave the conservative prediction of the crack growth behavior.