An Advanced 12Cr Steel Rotor Applicable to Elevated Steam Temperature 593°C

The upper limit of steam temperature which 12Cr steel rotors can withstand has been considered to be 566°C, but the recent projects on the advanced steam turbine of large capacity demand to raise it. The key factor in upgrading the creep rupture strength of the existing 12Cr steel rotors is to adjust “Equivalent Molybdenum Content” to the optimum, which is 1.5 percent in case no tungsten is contained. A HP-IP rotor, of 11 tons in final machined weight, for EPDC’s Wakamatsu high-temperature turbine to be operated with 593/593°C steam, has been manufactured with the chemical composition of C 0.14, Si 0.08, Mn 0.51, P 0.013, S 0.001, Ni 0.60, Cr 10.23, Mo 1.48, V 0.17, Nb 0.056, N 0.045, and Al 0.002 percent, respectively, through ESR process, Its creep rupture strength after heat treatment is 122 MPa for 593°C and 10⁵ hr. The paper reports the concept of this material and the actual achievement in Wakamatsu rotor forging, referring to the working condition expected on the rotors for 1000 MW-class advanced steam turbine.