Requirements for and challenges in developing improved creep ductility-based constitutive models for tempered martensitic CSEF steels

Creep fracture behaviour of tempered martensitic steels is generally governed by the process of cavity nucleation, growth and coalescence into microcracks. Therefore, creep ductility, which can be treated as material resistance to damage, has a critically important implication on the creep performance of materials and components, particularly where mechanical and metallurgical constraints are present. This review deals with some key aspects relating to creep ductility of high-temperature materials, paying a specific attention to creep strength enhanced ferritic (CSEF) steels. In the present work, the currently available state-of-the-art creep ductility-based constitutive models are reviewed, and the predictive capabilities of these models, particularly under multi-axial stress states, are examined. On this basis, the main limitations and challenges associated with using the existing models are evaluated and identified, and the requirements for developing improved creep ductility-based models for CSEF steels in order to carry out more accurate service life assessments are addressed.