2001 Volume 87 Issue 8 Pages 564-569
The 2.25CrMoV steel is applied to conventional combined high-pressure (HP) and low-pressure (LP) rotor forging, and it has excellent creep properties and toughness at 538°C conventional steam temperature. However, at 566°C steam temperature, it is required to improve the properties of the rotor forgings. The effects of chemistry on toughness and creep rupture strength have been investigated on the 9CrMoV base materials for the purpose of developing a new HP-LP rotor material for 566°C steam temperature. Thus 9.8Cr1.4Mo1.0NiVNbN steel, named HLP9F, with higher toughness and creep rupture strength compared with conventional 2.25CrMoV steel, has been developed. A trail HP-LP rotor forging with the diameter of LP section of 1800 mm and that of HP section of 1200 mm has successfully been manufactured through the VCD process from 68 t ingot. In spite of a large ingot, neither chemical composition change nor eutectic Nb (C, N) formation could be recognized. The rotor, furthermore, exhibited satisfactory quality in toughness and creep rupture strength. This rotor material is suitable to the HPLP rotor material for advanced combined cycle steam turbine.
