PRACTICAL APPLICATION OF AN ADVANCED 12CR-ROTOR TO 593-DEGREES-C-700MW STEAM-TURBINE PLANT

The largest class IP rotor forging with 1 200 mm in maximum diameter, for steam turbine of 700 MW class to be operated at 538/593-degrees-C steam temperature, has successfully been manufactured with an advanced 12Cr rotor material which we call this alloy TMK1, through the electroslag remelting (ESR) process from 55 t ingot. The quality and material characteristics of this advanced 12Cr rotor forging were evaluated for various locations of this rotor. In spite of a large ingot, neither chemical composition changes nor mechanical properties differences with positions in the rotor could be recognized. This is due to the ESR process and the advantages of the ESR are fully exhibited. Significant improvements in toughness and creep rupture properties were recognized in this rotor forging. Especially, the improvement of creep rupture strength in this advanced 12Cr steel is mainly attributed to dispersion strengthening by V4C3 and NbC in addition to solid-solution strengthening by Mo. It was confirmed that this rotor had sufficient characteristics for a large 12Cr steel rotor for 593-degrees-C steam temperature.