Tertiary creep behaviour of 9Cr-1Mo ferritic steel

The paper presents tertiary creep behaviour of thick section 9Cr-1Mo ferritic steel forging at 793 and 873 K. The stress dependence of rupture life obeyed power law. The steel exhibited distinct low and high stress regimes characterised by separate values of power law exponent and constant in the creep rate-rupture life relationships of Monkman-Grant type. Extensive tertiary creep in terms of both the large time spent and the large creep strain accumulation during tertiary creep has been observed. The prolonged tertiary creep was associated with the high and distinct values of creep damage tolerance factors in the low and high stress regimes indicating dominance of microstructural degradation in the steel. Separate master creep curves have been obtained for low and high stress regimes in the coupled relationship for creep deformation and damage that depends only on creep damage tolerance factor envisaged in the continuum damage mechanics approach.