Multiaxial Creep Rupture Life Evaluation for Austenitic Stainless Steels Using Weld‐Type Miniature Cruciform Specimen

ABSTRACT A multiaxial creep testing technique using a weld‐type miniature cruciform specimen was developed to evaluate the creep properties and rupture life of Super 304H austenitic stainless steel at 973 K (700°C). The cruciform specimen was designed to achieve a plane stress state and overcome material dimensional limitations. In situ observations revealed no significant intergranular cracking on the specimen surface up to a life ratio of 0.9, regardless of the stress condition. Creep curves obtained using the nominal strain calculated by a non‐contact measuring method showed no clear transition region and exhibited ductile rupture with an accelerated strain increase from a life ratio of 0.6. The Mises equivalent stress parameter effectively evaluated the multiaxial creep rupture life within a factor of 2 compared with the uniaxial data. These findings contribute to the understanding of the multiaxial creep behavior and life evaluation of Super 304H, which is an important material for high‐temperature applications.