Creep-rupture tests on chromium-containing conventional and ODS steels in oxygen-controlled Pb and air at 650°C

•Generally superior creep performance of ODS steels with 12–14% Cr is indicated.•Strength of 9Cr-ODS at 650̊C approaches conventional 9Cr steels at decreasing load.•ODS steels show brittle primary and ductile residual fracture.•Apparent link between secondary creep rate and fracture mode of ODS steels.•Clear impact of liquid Pb at low load, corresponding to long time-to-rupture. Conventional martensitic steels with 9mass% chromium (Cr), namely T91 and P92, and ODS steels with 9, 12 and 14mass% Cr, respectively, were subjected to creep-rupture tests in stagnant oxygen-controlled lead (Pb) at 650°C and co=10−6mass% dissolved oxygen. The 9Cr conventional steels were tested in the liquid metal at static engineering stress in the range from 75 to 200MPa. 12 and 14Cr ODS were tested at 190–400MPa, and 9Cr ODS at 75–300MPa. Reference tests in stagnant air were carried out in the same stress ranges. The ODS steels with 12 or 14mass% Cr, mainly tested in oxygen containing Pb, clearly exhibit a change in the stress-dependence of secondary creep rate and appearance of fracture surface at 330–400MPa. No such change has been observed for 9Cr ODS so far. The conventional martensitic steel P92 shows a significant drop in creep strength accompanied by reduced necking and a change from ductile to brittle fracture when tested in Pb at 75MPa (time-to-rupture tR=13,090h).