HIGH CREEP-STRENGTH ALLOYS

Current coal-fired supercritical-steam power plants currently operate with steam boiler and turbine inlet temperatures at about or slightly above 600oC. New ultra supercritical (USC) steam power plants will require boiler tubing and turbines capable of reliable operation at steam temperatures up to 760oC. ORNL has been involved in alloy development of a wide range of steels, stainless steels and alloys, and various superalloys with more creep-strength and temperature capability based on careful design and control of microstructures. This paper highlights recent processes in three areas relevant to USC steam conditions, including modifications of wrought and cast stainless steels that correspond to grade 347 stainless steels, modifications of bainitic 3Cr and martensitic 9Cr steels, and studies of processing effects on the new 740 alloy (introduced by Special Metals)