Creep Rupture Properties of 12%Cr Steel Rotor for an Ultra Super Critical Steam Turbine

Abstract

To improve the heat rate in the thermal power station, the development of an ultra super critical steam turbine has projected. A 12%Cr steel rotor forging which has higher creep rupture strength than conventional rotor forging has been required as the turbine rotor for a steam temperature of 593°C. Creep rupture strength at 593°C for 10⁵ h has been required to be over 10 kgf/mm².
To achieve this requirement, the effect of carbon and nitrogen contents on creep rupture properties were studied using small laboratory heats based on low Si-10Cr-1.5Mo-0.05Nb-0.17V series steels. The excellent creep rupture properties were observed at the range of C: 0.130.15%, N : 0.040.05%.
Based on the results of laboratory heats, the rotor forging for the demonstration tests was manufactured from 39 t ESR ingot. Creep rupture strength at the center core of the rotor forging was 12.4 kgf/mm² at 593°C for 10⁵ h. No drop of creep rupture ductility and no notch embrittlement were observed even for long term tests.