2004 Volume 90 Issue 4 Pages 206-212
The long-term creep rupture testing was conducted on 9Cr-1Mo-V-Nb steel welded joint to obtain its creep rupture properties and microstructural changes during creep. From these data the relation between the microstructural change and the initiation and propagation of a creep crack was examined. Creep rupture tests were done at three temperatures of 823K, 873K, and 923K, under the stress ranges of 160-230 MPa, 80-130 MPa, and 40-80 MPa, respectively. In order to investigate the stress and strain distribution of the welded joint specimen that showed the type IV fracture in the low loading stress range at 873K and 923K, finite element method (FEM) analysis was carried out using the creep data of simulated HAZ specimen. The analysis revealed that the stress triaxiality is higher in the fine grained HAZ region adjacent to the base metal than in the other parts. The analysis combined with the experimental results suggests that creep crack would initiate at the fine grained HAZ region adjacent to the base metal at the location of transition in groove angle in the welded joint and would propagate toward the upper part of the V groove along the V groove in the region.
