Design and Exploration of High-Temperature Steels for Electric Power Generation Applications

Northwestern University, Evanston IL

Investigators

Abstract

Increasing the efficiency of electric power generation helps reducing fuel consumption and carbon dioxide emission. About 80 percent of the electricity in the U.S. is generated with steam turbines whose efficiency is limited by their maximum operating temperature. This award supports fundamental research to develop economically viable steels that can be used at substantially higher temperatures than those used in steam generators today, in order to increase their energy conversion efficiencies. Benefits for the U.S. economy and society will be multidimensional: in addition to potential savings in fuel cost and reduced emissions in power generation afforded by these new alloys, this research will advance the knowledge base for designing improved high-temperature alloys by deepening the understanding of how processing and the resulting microstructure bring about the improved properties of a newly designed material. This research aims to develop the intellectual basis for designing high-temperature resistant steels that can be used in high-efficiency ultra-supercritical steam generators for electric power plants at temperatures above 650C (1200F). This involves a novel combination of several strategies in steel design: utilizing a fine dispersion of semi-coherent mono-carbide or carbo-nitride precipitates, additions of molybdenum or tungsten for solid solution strengthening, and optimizing the carbon concentration to suppress formation of precipitate phases detrimental to creep strength. The underlying scientific concepts include minimizing interfacial energies and diffusion to reduce the rate of coarsening, and semi-coherent interfaces between precipitates and the matrix to create obstacles for impinging dislocations for improved high-temperature strength. In pursuing these design principles, computational thermodynamics, precipitation modeling, micro- and nanostructural characterization by optical, transmission-electron and atom-probe microscopies, and evaluation of high-temperature mechanical properties will contribute to a multidimensional understanding of the processes governing the high-temperature creep strength, ultimately leading to the development of new alloys with improved properties.