Creep-oxidation interaction of a new martensitic steel 9Cr3W3Co in water vapor at 650 °C

In this study, the creep tests in air and water vapor environment at 650 & DEG;C under 155-220 MPa were carried out to study the effect of water vapor on the creep property, creep deformation and creep fracture mechanisms of 9Cr3W3Co steel. The results indicated that the water vapor environment did not affect the creep deformation mechanism but affected the creep behaviors and life, which was determined by the stress level. Under the high applied stress level (& GE; 180 MPa) in water vapor, the thin oxide particle dispersion strengthening layer formed on the surface increased the strength of the subsurface structure, which led to a decrease in the steady-creep rate and an increase in the time of the steady-creep stage than that in air. On the other hand, the crack blunting caused by the recrystallization of microstructures ahead of crack tip delayed the creep fracture. As a result, the creep life increased in the water vapor environment. Under low applied stress (& LE; 155 MPa) in water vapor, the increase of cavities number in the inner oxide layer and cracks number on the oxide film/matrix interface led to the reduction of the effective bearing area of the material, and thus the steady-state creep rate increased and the time of steady-state creep stage decreased. Different creep damage forms induced by the interaction of different applied stresses and creep environments affected creep fracture process and creep life. Oxidation in water vapor accelerated the connection of existing creep cavities on lath boundaries by promoting crack growth, thereby accelerating creep damage, which led to a significant reduction in creep life.