DI GIANFRANCESCO Augusto Centro Sviluppo Materiali

Spoluautoři NERI Stefano, CALDERINI Massimo, FORONI Luca, MONTANI Raimondo

The 718 is a very well know superalloy developed in the years ’60 worldwide used for aircraft engine, petrochemical plants, oil and gas applications, with a very wide operating temperatures spectrum with an upper limit close to 650°C. The continuous trend in efficiency improving for the new fossil fuel fired plants for power generation needs an increasing in temperature and pressure of the critical components: boiler and turbine. Therefore the tubes, cast and forged components in the hottest part of the plant are hardly stressed and steel and alloys with improved creep performances are required. The steam turbine inlet temperature for the new generation plants is scheduled in the range of 720°C with a pressure of 350MPa and the high and intermediate pressure rotor sections are going to be produced in superalloys. In the frame of the Thermie Advanced (700°C) Pulverised Fuel Power European Project a trial rotor disk has been forged by Società delle Fucine in Italy using a billet produced by AOD + double VAR remelting at Acciaierie Foroni. A new heat treatment was developed by Centro Sviluppo Materiali to increase the microstructural stability in the range of 650-750°C and to improve the creep behaviour. Now the longest creep tests are approaching the 100.000 hours and a creep data assessment show an increase of about 50°C respect to the standard UNS718 material. This work summarize the 12 years of work done that could now open the possibility of use the 718 superalloy up to 700°C for forged components in the new steam turbine for the Advanced Ultra Supercritical Power Plants.

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