Published: Jan 1986
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Steel Grade X5 Cr-Ni-Mo 12 6 containing 0.05% carbon, 12% chromium, 6% nickel, and 1.50% molybdenum is an advantageous material for turbine rotors in geothermic power stations because of its excellent strength and toughness properties in combination with good erosion and corrosion resistance.
In terms of the phase diagram, this soft-martensitic steel has its place at the martensite/austenite/ferrite interface. Therefore, its chemical composition must be chosen so as to have a completely martensitic structure after hardening. During tempering above 773 K (500°C), austenite is precipitated in finely dispersed form in the tempered martensite. This secondary austenite improves the toughness, is extremely stable, and does not transform even at temperatures down to approximately 73 K (-200°C).
The manufacture of and the mechanical properties of a turbine rotor 1200 mm in diameter by 5600 mm in length with a finished weight of approximately 21.5 tons are described in detail.
soft-martensitic stainless Cr-Ni-Mo steel, turbine rotor, geothermic, high toughness combined with good strength, austenite formation during tempering
Engineer, Quality and Materials Engineering, ARBED Saarstahl, Völklingen,
Chief engineer, Quality and Materials Engineering, ARBED Saarstahl, Völklingen,