Elevated-temperature Strength and Hot Corrosion Resistance of 2OCr-25Ni Steel for Tubes in Ultra-supercritical Power Boilers

The two oil crises of 1973 and 1975 spurred the development of ultra-supercritical power plants for greater energy savings by higher steam temperature and pressure. The development project has been mainly led by the Electric Power Development Co. Ltd. in Japan and Electric Power Research Institute in the United States. Since the existing steels are not strong and corrosion resistant enough to meet the intended application, it is a pressing need to develop high-strength steel for boiler tubes that can withstand the intended ultra-supercritical steam temperature and pressure. After study of solid solution strengthening of the matrix, precipitation strengthening, prevention of sigma phase formation and other factors involved in austenitic heat-resistant 20Cr-25Ni-1.5Mo-Nb-Ti-N steel has been developed. The steel has creep rupture strength of over 88 MPa at 700°C and 100000 h and excellent corrosion resistance, and can be produced by continuous casting.