Creep-to-rupture of 12Cr- and 14Cr-ODS steels in oxygen-controlled lead and air at 650 °C

Ferritic and ferritic/martensitic oxide dispersion-strengthened (ODS) steels are a promising class of materials with high potential for application at high temperature and irradiation. Creep-to-rupture behavior of such steels with 12 and 14 mass% chromium (Cr) was tested in stagnant oxygen-controlled liquid lead and air at 650 °C and 125-400 MPa engineering stress. Liquid Pb affects insignificantly creep strength of both steels in comparison to air. In general, 12Cr-ODS shows slightly better creep performance than 14Cr-ODS. A significant change in the stress exponent n of the Norton occurs around 330 MPa and 380 MPa for 12Cr- and 14Cr-ODS, respectively, pointing at a change in creep mechanism of the ODS steels. Additionally, brittle fracture at low stress or strain rate changes to ductile fracture at high stress/strain rate as indicated by increasing necking and strain at rupture.