This study evaluated the multiaxial creep properties and creep rupture life of Super304H using a welded miniature cruciform specimen. The material to be evaluated was used only for the central gauge part of the cruciform specimen, and separately prepared parts were welded to the loading griping part to minimize the size of the evaluated material. Deformation in the central gauge part of the weld-type cruciform specimen was larger at the SUS316 gripping area than at the Super304H gripping area. However, there was no significant effect of the different gripping materials on the creep rupture life under the testing conditions of 973 K and 180 MPa equivalent stress. Under the unequal biaxial tensile condition, the creep strain in the direction of minimum principal stress was significantly smaller than the strain in the direction of maximum principal stress. It is suggested that von Mises equivalent stress is effective for creep rupture life correlation. Although the multiaxial creep rupture lives show a tendency to be slightly longer than the uniaxial creep rupture lives, the equivalent stresses indicate that they can be correlated within a factor of 2.
