1998 Volume 84 Issue 3 Pages 236-241
CrMoV (1Cr-1Mo-0.25V) rotor steel is commonly utilized for high pressure (HP) or intermediate pressure (IP) turbine rotor forgings used at steam temperature up to 566°C. The steel has excellent mechanical properties at elevated temperatures, especially creep rupture strength. Improved toughness of the CrMoV rotors, however, is desired in order to minimize the warm-up time of the turbine system. In this study, a fundamental examination was performed using small laboratory ingots. Optimal chemical composition and heat treatment conditions of developed CrMoV rotor steel were selected to obtain good fracture appearance transition temperature (50%FATT) without loss in the creep rupture strength. Toughness was improved by decreasing the silicon content (VCD : Vacuum Carbon Deoxidation) and increasing hardenability to a level greater than conventional HP rotor forgings. The toughness was also improved by accelerating the cooling rate by oil quenching instead of blast cooling. Based on the knowledge obtained through the fundamental study, actual full size HP/IP rotor forgings were manufactured. As test results, it was verified that these rotor forgings show higher toughness along with excellent creep rupture strength.
