The role of primary and tertiary creep in defining the form of the Monkman-Grant relation using the 4-θ methodology: An application to 12Cr-Mo-V-Nb steel

It is important to be able to predict the life of materials at high temperatures. The Monkman-Grant relation offers potential for reducing the development cycle for new materials. This paper uses the 4-θ methodology to i. identify and explain the form of this relation in terms of creep mechanisms and ii. to discover whether this form is compatible with development cycle reduction. The Monkman-Grant proportionality constant (M 2 ) was found to fall into three groupings depending on the amount of damage and the rate at which this occurred. Only once this was considered did the exponent on the secondary creep rate equal −1 – as predicted by 4-θ methodology. One of these groupings might be relevant for longer term life assessment.