Difficulties in modelling creep rupture data due to inconsistencies between the batches tested under different temperature and stress conditions are discussed, in relation to the methodology of model formulation. It is demonstrated how such problems may be overcome using the P-NID modelling procedure. The limitations of statistical methods for evaluating models are examined.
Sanicro 25 is a heat-resistant steel with high performances used in the advanced ultra-super critical power plants. This paper provides a discussion on the creep-fatigue interaction behaviours of this steel with different strain ranges and dwell times at 700 degrees C. The influences of dwell time on the cyclic deformation behaviours and life time have been evaluated. Increase of dwell time will generally decrease number of cycles but increase the time to failure. The influence of dwell time at a large strain on the life cycle is small. Dwell time can significantly impact both the initiation and propagation of cracks during a creep-fatigue interaction process, resulting in more intergranular cracking. The influences of dwell time on the cyclic plastic deformation, precipitation behaviour, recovery phenomena, and crack initiation and propagation have also been discussed. Fracture investigations show that dwell time results in more intergranular cracking.
