Development of a Design Methodology for High-Temperature Cyclic Application of Materials Which Experience Cyclic Softening.

摘要

The project described in this report has, as its beginning, two investigations, the first a study of the effect of material softening on the overall structural stability of complex components, and the second an evaluation of damage induced through cyclic loads combined with high temperature environmental effects. The initial work was carried out on one grade of 2.25Cr 1Mo steel, with the intention of extending the investigation to other grades once the investigative techniques had been settled. However, considerable interest has grown in the application of modified forms of austenitic steel to very high temperature use in superheaters and reheaters. The ability to utilize these materials can mean an increase of 100(degree)C in the top temperature in a power plant, which converts into a significant improvement in thermal efficiency for a very small investment in material. Therefore, the direction of this project has been modified to continue on this class rather than the ferritic alloys originally under consideration. The basic problem to be investigated in the austenitics is the concern for possible strength variations, either positive or negative, induced in the very complex microstructures by service conditions of cyclic load and high temperature. 23 refs., 31 figs., 6 tabs.