Development of Integral High-Pressure—Low-Pressure Combination Rotor Forgings

Abstract

Integral high pressure (HP)-low pressure (LP) combination rotor forgings for single-cylinder turbines used under the steam condition over 773 K require good toughness and elevated temperature strength. Conventional Ni-Cr-Mo-V or Cr-Mo-V steel forgings are undesirable from the viewpoint of material properties. We developed integral HP-LP combination rotor forgings by alloy modifications (niobium and nickel addition) based upon Cr-Mo-V steel and the application of differential heat treatment. An actual dimensional prototype sample forging (1650 mm in diameter) was manufactured and evaluated. The forging exhibited high quality, and superior creep rupture strength at the HP zone and excellent toughness at the LP zone were obtained simultaneously. These developed rotor forgings have been applied for several turbine units of about the 100-MW class.