CREEP BEHAVIOUR AND MICROSTRUCTURAL CHANGES IN 9 – 12Cr STEELS UNDER NONSTEADY LOADING

摘要

Creep behaviour and damage processes in creep of advanced 9-12%Cr power plant steels are phenomena of major practical relevance, often limiting the lives of power plant components and structures designed to operate for long periods under stress at elevated temperatures. Although the development and evaluation of advanced 9-12%Cr steels have proceeded on the basis of simply laboratory – type tests, it is widely recognized that the realistic application of these materials is under conditions far different from those for which they were developed. Thus methods of creep property assessments based on physical changes in the material that are likely to occur during service exposures rather than simple parametric extrapolation of the short-term data are necessary. rnThe present investigation was conducted on three advanced 9-12%Cr ferritic steels (P91, P92 and E911) in an effort to obtain more complete description and understanding of the role of degradation processes in high temperature creep under nonsteady loading. A comparison between the creep characteristics of nonsteady and monotonously loaded creep specimens has revealed no significant deterioration of the creep strength and fracture resistance of the steels P91, P92 and E911 under non-steady loading in power-law (dislocation) creep. The final part of this paper deals with detailed microstructural and fractographic investigations of crept specimens to explain the observed creep behaviour.