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Alleima® 4C54 is a ferritic, stainless chromium steel for use in high-temperature applications such as recuperators in the metallurgical and glass industries and thermocouple protection tubes.
The grade is especially suitable for sulfurous flue gas atmospheres and can be used at temperatures up to 1100°C (2010°F), depending on the service parameters and application. The ferritic structure of Alleima® 4C54 also gives it good resistance to extremely corrosive metal melts, such as copper, tin and lead.
The grade's extremely good resistance to reducing sulfudizing gases and salts, compared with austenitic stainless steels, is due to the high chromium content and absence of nickel. Alleima® 4C54 also exhibits excellent resistance to isothermal and cyclic oxidation in air.
A large, German steel manufacturer wanted to change existing low-alloy recuperator tubes to a material with longer service life. Tubes would be required to resist temperatures up to 1000°C (1832°F) in a sulphur-rich* atmosphere.
Alleima material specialists recommended Alleima® 4C54 and in 2008, the German company installed 2000 meters of high-temperature grade tubes from Alleima in one of the recuperators. The tubes have now been in use for 3.5 years (2012), without any problems or production stops. This is already twice as long as the previous low-alloy tubes.
* The combustion gases consisted of 3% O2, 12% CO2, 6% H2O polluted with 1500–2000 mg of SO2. The maximum outlet combustion temperature was 1000°C (1832°F) and the maximum wall temperature of the tubes reached 850°C (1562°F).