Iron Chromium Aluminium Alloys – Rescal

Those are alloys of chemical composition Fe + Cr + Fe with some additional elements and rare earth so as Yttrium, zirconium, Titan, Cerium, and Lanthanum which confer them:

• An excellent resistance to oxidation under heat
• A limitation of intergranular oxidation
• A good life time

Alloys in question are:

Resistohm 125 – 135 – 140 – 145 – Y

Their metallurgical structure confers them nevertheless a cold plasticity lower than austenitic alloys (NiCr).

Advantages of FeCrAl compared with NiCr

• A higher resistivity (until 1.44 ohm mm²/m)
• A temperature of use higher in the air (1300°C against 1200 °C for Resistohm 80)
• A higher charge rate
• A good resistance to sulphurous and carbonaceous atmospheres
• A lower density which means: with an equal weight of material a more important number of elements (a cheaper unit price)

However

• A less important plasticity and a more difficult shaping
• Mechanical behaviour limited and embrittlement after first heat
• Possibility of corrosion more important because of the iron
• Phenomenon of “path” more important (striction and elongation of the resistances)

Constraints

• Pre-oxidation often necessary
• Minimal content in alumina of the supports: 60 % without iron oxide
• In furnaces under atmosphere, initial coat of protective oxide to regenerate periodically.