EFFECT OF CHEMICAL-COMPOSITION AND MANUFA CTURING PROCEDURE ON TOUGHNESS OF CRMOV HP ROTOR FORGINGS

CrMoV (1Cr-1Mo-0.25V) rotor steel is commonly utilized for high pressu re (HP) or intermediate pressure (IP) turbine rotor forgings used at s team temperature up to 566 degrees C. The steel has excellent mechanic al properties at elevated temperatures, especially creep rupture stren gth. Improved toughness of the CrMoV rotors, however, is desired in or der 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 develo ped CrMoV rotor steel were selected to obtain good fracture appearance transition temperature (50%FATT) without loss in the creep rupture st rength. Toughness was improved by decreasing the silicon content (VCD: Vacuum Carbon Deoxidation) and increasing hardenability to a level gr eater than conventional HP rotor forgings. The toughness was also impr oved by accelerating the cooling rate by oil quenching instead of blas t cooling. Based on the knowledge obtained through the fundamental stu dy, actual full size HP/IP rotor forgings were manufactured. As test r esults, it was verified that these rotor forgings show higher toughnes s along with excellent creep rupture strength.