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

A low alloy steel ingot includes: 0.5-0.30 % of C; 0.03-0.2 % of Si; 0.5-2.0 % of Mn; 0.1-1.3 % of Ni; 1.5-3.5 % of Cr; 0.1-1.0 % of Mo; more than 0.15 and equal to or less than 0.35 % of V; optionally Ni; and the remainder consisting of Fe and other unavoidable impurities. The present invention performs quality heat treatment including a hardening step and a tempering step of the low alloy steel ingot so that a substance has a grain size number of 3 to 7, doesn′t have free ferrite in a metallographic structure, and has tensile strength of 760 to 860 MPa and fraction transition temperature not higher than 40°C.