Superclean 3.5NiCrMoV turbine rotor steel: a status report. I: Steelmaking practice, heat treatment, and metallurgical properties

Recent international research has resulted in the development of superclean 3.5NiCrMoV steel for low pressure turbine rotors. Such steel is highly resistant to temper embrittlment and will thus facilitate increased efficiency in electricity generation through the use of higher operating temperatures and improvements in design. Steels with impurity contents typical of the superclean specification can be manufactured for production rotors with properties that equal or exceed those for conventional 3.5NiCrMoV rotors in every detail. Of particular interest are the observations that the superclean steels appear to be virtually immune to temper embrittlement and may be used up to their creep limited temperature of 500 deg C (932 deg F). An introduction to the steelmaking practices and heat treatments used to produce full sized production rotors is presented along with resulting metallurgical properties. Graphs. 36 ref.--AA