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INTERNATIONAL TUNGSTEN INDUSTRY ASSOCIATION
Information on tungsten: sources, properties and uses
Heat Resisting Steel and Cast Steel
In certain cases, tungsten is added when steels are used in higher temperature ranges. Heat resisting steels are either chromium nickel steels with up to 6% tungsten, or heat treatable 9-12% Cr-steels, where tungsten is added in the range of 1-2% to improve the creep resistance and long-term stability of the steels.
The main use for austenitic Cr/Ni steels is as valve steels for combustion engines, which contain around 2% W. Similar steels are used for components of steam and gas turbines, such as blades, discs, bolts and pins. Heat treatable creep resistant chromium steels can be used up to about 620°C for continuous operation in power plants. They are currently considered to possess the maximum creep strength of all heat-resistant steels for boiler components and piping systems. Such steels are also used in a slightly modified form for large cast chromium steel components in steam power plants, such as inner and outer casings or valve housings in the high pressure and medium pressure part of the turbine.