Short Creep-Fatigue Crack Growth in an Advanced 9 %Cr Steel

Abstract

While the development of short cracks due to cyclic elastic loading has been relatively widely studied, in particular at room temperature, their consideration for cyclic inelastic loading at high temperatures and lower frequencies is not so common. Short creep-fatigue crack growth rates may be correlated in terms of cyclic strain range, cyclic J-integral or strain energy density factor, with appropriate allowance for associated creep damage accumulation. Candidate approaches are evaluated with reference to test results generated for an advanced 9 %Cr turbine rotor steel. This paper promotes the use of cyclic strain range and strain energy density factor relative to other candidate correlating parameters in relation to the results of a series of 30 min hold time creep-fatigue tests performed using fully instrumented uniaxial specimens with short crack starters. The focus of the testing campaign is an advanced 9 %Cr turbine rotor steel at temperatures of 600 and 625 C.