Selection Guide - Choosing FeCrAl or NiCr Heating Alloys

Selection table

Criterion	Condition	Recommended	Reason
Element temperature	Below 950 °C	1Cr13Al4 or 0Cr23Al5	Lowest cost; adequate oxidation resistance
Element temperature	950 - 1100 °C	0Cr25Al5	General-purpose; leave 50-100 °C margin
Element temperature	1100 - 1300 °C	0Cr21Al6Nb	Niobium resists grain growth and sagging
Element temperature	Above 1300 °C	0Cr27Al7Mo2 or radiant tubes	Consider silicon carbide if above 1400 °C
Atmosphere	Clean air / oxidising	Any of the above	Standard selection applies
Atmosphere	Sulphur-bearing	FeCrAl only	Sulphur attacks NiCr; low-melting nickel sulphides form
Atmosphere	Carburising	NiCr preferred	FeCrAl oxide film may reduce; carbide ("green rot") forms
Atmosphere	Vacuum / dry hydrogen	NiCr preferred	FeCrAl loses aluminium by volatilisation
Duty	Frequent cycling / repeated dismantling	NiCr (Cr20Ni80)	Better room-temperature ductility and thermal fatigue

Five-step selection

Confirm the actual element temperature (not furnace temperature) and set the grade boundary with 50-100 °C margin.
Check the furnace atmosphere and exclude unsuitable materials (no NiCr in sulphur-bearing atmospheres).
Calculate the required resistance from voltage and target power: R = U² / P.
Derive diameter or strip cross-section, then check surface load and support spacing.
Confirm dimensional fit, terminal arrangement and expansion allowance before ordering.

Surface load reference

Temperature range	Typical surface load
Below 700 °C	2.0 - 3.0 W/cm²
700 - 1000 °C	1.5 - 2.5 W/cm²
1000 - 1150 °C	1.3 - 2.2 W/cm²
Above 1150 °C	1.0 - 1.8 W/cm²
Inside radiant tubes	0.8 - 1.5 W/cm²

Typical values and experience-based estimates. Final selection must be verified against actual working conditions, furnace geometry and support arrangement.

FAQ

How do I choose the element temperature?

Use the element temperature, not the furnace temperature. The element runs tens to over a hundred degrees hotter than the furnace; selecting by furnace temperature removes that margin entirely.

What surface load should I use?

Typical values: 2.0-3.0 W/cm² below 700 °C, 1.5-2.5 W/cm² at 700-1000 °C and 1.0-1.8 W/cm² above 1150 °C. Long holds and frequent cycling call for the lower end.

Why did power change after replacing the element?

Because resistivity or cross-section changed, or the cold resistance was used for calibration. FeCrAl resistivity rises by more than 10% when hot, so power checks should use hot resistance.