Advanced technology in creep life prediction and damage evaluation for creep strength enhanced ferritic steels

Abstract

Creep damage mechanisms of recently developed boiler and steam-turbine steels are not well clarified, however, creep life prediction technology for such creep strength enhanced ferritic steels, grades 91, 92 122, etc. with tempered martensitic structure including welds has been strongly demanded by power plant operators and equipment manufacturers. In this paper, the technologies related to the creep life prediction and damage evaluation for creep strength enhanced ferritic steels being studied from the various aspects in Japan will be surveyed and presented. The creep life prediction of this type of steel must be grounded on the findings on microstructural degradation and creep softening in martensitic structure composed of very fine martensite lath, block, packet and prior austenite grains, and precipitation and dislocation structures. Physical properties response to the creep degradation and measurement and detection of localized creep damageystrength would be useful tools to develop diagnostic techniques for life prediction of creep strength enhanced ferritic steels. Other important techniques to support the creep life prediction based on creep-strainyrupture data are creep modelling and data analysis which have been successfully investigated to date.

Guest Editorial: Personal perspective on microstructure of steels: 25th anniversary of MST and collection of papers in honour of Sir Robert Honeycombe

“…Turning now to creep resistance, there has been substantial international activity with the goal of designing steels which can survive 100 MPa of stress at 650uC over a service period of 25 years or more, bearing in mind the requirements of weldability, oxidation resistance and cost. 30,31 These are demanding requirements and early theoretical work 32 indicating new designs failed to live up to its predictions 33 because of the unexpectedly rapid formation of undesirable phases and failure to take account of oxidation. Similarly, large experimental programmes have systematically failed to achieve the targets for two reasons.…”