Inherent creep strength and long term creep strength properties of ferritic steels

Inherent creep strength is defined as a constant creep strength independent of time and microstructure. Sigmoidal inflection of a relation between stress and time to rupture is explainable in terms of a loss of creep strength followed by the advent of inherent creep strength. Although a large variation of short term creep rupture strength is observed, inherent creep strength is evaluated to be almost the same for several low alloy Cr-Mo steels. Creep rupture strength of the 12Cr-1Mo-1W-0.3V steel is higher than the other steels investigated in the short term region, however, it decreases with decrease in stress abruptly and it is almost the same as common inherent creep strength for low alloy Cr-Mo steels. On the other hand, creep rupture strength of the modified 9Cr-1Mo steel is higher than the other steels even at low stresses.