Creep behavior and rupture life of the simulated intercritical HAZ for 1.25Cr-0.5Mo steel under a mu.pdf

1. Introduction In order to predict the creep life of an actual component such as a pressure vessel, the influence of a mutiaxial stress state upon creep behavior should be considered. Thus, sig- nificant efforts have been made to establish the criterion to determine the multiaxial creep life. A couple of concepts have been developed to clarify the above issue. In the con- cept developed by Hayhurst1) and Cane,2) the maximum principal stresses and equivalent stress differently affected the creep behavior and the contribution of each stress to rupture life varies depending on materials. Al-abed et al.3) examined the notched bar creep behavior of ferritic steels and found that rupture life of brittle Coarse Grained HAZ of 2.25Cr–1Mo steel was predominantly determined by the maximum principal stress. On the other hand, that of duc- tile parent material of 2.25Cr–1Mo steel was almost solely dependent on the equivalent stress. They ascribed the dif- ferent dependence on each stress to the inherent ductility of material. Therefore, the material’s response to a multiaxial stress state must be known for the life assessment. Consid- ering the frequency of creep failures at the welds, the multi- axial creep behavior of the most vulnerable region, Inter- critical HAZ (ICZ), is a high-priority theme. To clarify the effect of a multiaxial stress state upon creep behavior, the creep test using a notched bar is the most accessible technique since it can be performed with a conventional creep machine. Thus, a code of practice was established by the European collaborative project4) in order to derive the multiaxial rupture life (trm) by notched bar creep rupture testing. In that approach, trm is correlated with uniaxial rupture life (tru) by the combination of the equiva- lent stress and the maximum principal stress or the equiva- lent stress and the hydrostatic stress. However, the information on the multiaxial creep behav- ior of ICZ is rather limited. Thus, in this paper, the eff