Generation of creep-fatigue interaction diagram for modified 9Cr-1Mo steel

The selection of structural materials for elevated temperature applications relies on the availability of proper design codes based on adequate data pertaining to the properties at service-relevant loading conditions. Two of the most widely used high temperature design codes, viz, the ASME Boiler and Pressure Vessel Code and the RCC-MRx code are at variance with each other on the bilinear interaction point in the creep-fatigue interaction diagram for modified 9Cr-1Mo ferritic steel. In view of this, a detailed investigation was carried out on the creep-fatigue interaction behavior of this alloy with special emphasis on the evaluation of the creep-fatigue damage and construction of the interaction diagram. Tests were performed on two chemical variants of the steel at two temperatures (773 K and 823 K) using the strain amplitudes of +/- 0.25%, +/- 0.4%, +/- 0.6% and +/- 0.8%. Hold times of different durations in the range, 1-60 min, were imposed in the tensile and compressive peak strains to introduce the creep damage. The ASME creep-fatigue interaction diagram was observed to be a more conservative design approach for the alloy.

Automated summary

The study on the creep-fatigue interaction behavior of modified 9Cr-1Mo steel reveals that the ASME code provides a more conservative design approach for this alloy.