Effect of oxidation on the creep rupture life of ASME T23 steel

The creep rupture behavior and the effects of oxidation on the creep strength of ASME T23 steel have been investigated. At 625 °C and 650 °C, a greater degradation of long-term creep strength was observed than expected from conventional master curve descriptions in the literature. Oxide scales were observed around the surface of the crept samples tested in air at 625 °C and 650 °C but no oxide scales were observed on samples tested in helium. However, at 625 °C, the creep rupture life was almost the same both in helium and in air, indicating that factors other than oxidation are responsible for the reduction in long-term creep strength. At 650 °C, the creep rupture life was longer in helium than in air, indicating an influence of oxidation, but the long-term strength in helium was still below the master curve. Reasons for the long-term degradation of strength, including microstructural changes, are discussed.