Fe-Cr-Al Alloys

Fe-Cr-Al Alloys:Cr13Al4, Cr21Al4,Cr20Al5, Cr21Al6, Cr23Al5, Cr25Al5, Cr21Al16Nb, Cr27Al7Mo2, Resistivity 1.25-1.53 ohm mm2/m

RESISTANCES OF TYPE Fe-Cr-Al

Ferritic alloys allow to reach process temperatures of 2192 to 2282°F, corresponding to a resistance temperature of 2372°F.All ferritic alloys have approximatively the same basis composition: 20 to 25 % of chromium, 4.5 to 6 % of aluminium, balance being iron.Some of them contain in addition rare earth, as Yttrium or Silicium.Those alloys having a ferritic structure, we observe, after a maintenance at high operating temperature, an important growth of the grain and a precipitation of chromium carbides at the grain joints level.This induces an increased embrittlement of the resistance, especially when it is come again at ambient temperature.

CORROSION

All the alloys FeCrAl form, in oxidising atmosphere, a protective coat of alumina.This alumina coat renews itself suitably as much as aluminium content is sufficient (about 2 %).This consumption of aluminium intervenes during scaling off of the oxide coat when this is subjected to thermic gradients.Addition of rare earths in the alloy,as Yttrium,permits to improve adherence of the oxide coat, and consequently to reduce phenomenon of scaling off.When content in aluminium is no more sufficient to ensure renew of oxide coat, it results a formation of chromium oxide on the surface. Degradation of the resistance is also especially speeder as temperature is elevated because oxide of chromium is volatile up to 2012 °F.

PROFESSIONAL ALCHROME AND FECRAL ALLOY PRODUCER IN CHINA

Fe-Cr-Al Alloys