Temperature, atmosphere, cycling. Get these three right and the grade choice is usually obvious.
There are dozens of grades and the datasheets all look similar. In practice, three numbers decide most of it.
Not furnace temperature. The element runs 50–150 °C hotter than the furnace, so the grade must be rated above the element temperature, not the furnace temperature.
| Element temperature | Suitable grades |
|---|---|
| below 800 °C | 1Cr13Al4, Cr15Ni60 |
| 900–1,000 °C | Cr15Ni60, 0Cr25Al5 |
| 1,000–1,100 °C | 0Cr25Al5, 0Cr21Al6Nb |
| 1,100–1,200 °C | 0Cr21Al6Nb |
| 1,200–1,300 °C | 0Cr27Al7Mo2 |
| above 1,300 °C | special alloys or non-metallic elements |
| Atmosphere | Note |
|---|---|
| Air / oxidising | normal use for both families |
| Nitrogen | fine, but watch the oxygen partial pressure |
| Hydrogen | reducing — attacks the oxide film, avoid FeCrAl |
| Vacuum | metal evaporates; heating alloys are generally unsuitable |
| Carburising | carbon pick-up embrittles the element |
| Sulphur-bearing | severe corrosion |
When the atmosphere is aggressive, Ni-Cr is the safer default.
| Pattern | Relative life |
|---|---|
| Continuous, 2 stops a year | 100% |
| 2 stops a week | 70–80% |
| 1 stop a day | 45–55% |
| 3+ stops a day | 25–35% |
Frequent cycling favours Ni-Cr because of its toughness.
Example 1 — 1,000 °C, air, continuous. 0Cr25Al5. Cheapest grade that meets the requirement. Example 2 — 1,000 °C, air, 3 stops a day. Cr20Ni80. Costs more, but survives the cycling. Example 3 — 1,200 °C, air, continuous. 0Cr21Al6Nb or 0Cr27Al7Mo2. Example 4 — 900 °C, hydrogen, continuous. Not a good fit for heating alloys. If it must be used, Cr20Ni80 at a reduced surface load.
Choosing the highest grade "to be safe". Higher grades are more brittle, harder to form, and more expensive. They do not automatically last longer — they last longer only if the operating conditions actually require them.
