Creep deformation behaviour and kinetic aspects of 9Cr-1Mo ferritic steel

This paper presents the detailed investigations on creep behaviour of 9Cr-1Mo ferritic steel with an emphasis to understand and unify the different stages of creep deformation in the framework of first order kinetic approach. The different values of stress exponent and apparent activation energy observed for the two stress regimes have been rationalized by invoking the concept of resisting stress. The detailed analysis of results revealed that both transient and tertiary creep obeyed first order kinetics with separate values of transient and tertiary creep parameters in the respective stress regimes. The two stress regimes with different values of stress exponent are manifested as separate master creep curves for transient and steady state creep. Similarly, the analysis of tertiary creep also revealed distinct master creep curves relating steady state and tertiary creep in the respective stress regimes. The paper also focuses attention on two important relationships, one obtained between transient and steady state creep, and the other between steady state and tertiary creep. The useful implications of these relationships in understanding the existing creep rate-rupture life relationships of Monkman-Grant type are also highlighted in this paper.