LOW ALLOY STEEL FOR GEOTHERMAL POWER GENERATION TURBINE ROTOR AND LOW ALLOY MATERIAL FOR GEOTHERMAL POWER GENERATION TURBINE ROTOR AND METHOD FOR MANUFACTURING THE SAME

摘要

According to the present invention, a low alloy steel ingot comprises: 0.15-0.30 wt% of C; 0.03-0.2 wt% of Si; 0.5-2.0 wt% of Mn; 0.1-1.3 wt% of Ni; 1.5-3.5 wt% of Cr; 0.1-1.0 wt% of Mo; more than 0.15 and equal to or less than 0.35 wt% of V; optionally Ni; and the balance of Fe and unavoidable impurities. The low alloy steel ingot can be performed quality heat treatment including a quenching step and a tempering step so that materials can have a grain size number of 3-7. Moreover, free ferrite is not provided in a metal structure, and tensile strength of 760-860 MPa and fracture surface transition temperature less than 40°C can be secured.