Inconel 601 and Inconel 600 are confused constantly because of the similarity of their names. 601 is NOT an “improved” version of 600 — it is a different alloy, made for a different job.
Two different purposes
A simple rule: Inconel 600 is a corrosion alloy, Inconel 601 is a heat-resisting alloy.
600’s nickel is at least 72 %; that high nickel gives it practical immunity to chloride stress corrosion cracking and resistance in caustic environments. 601 drops the nickel to 58–63 %, raises chromium to 21–25 % and adds 1.0 to 1.7 % aluminium.
What does the aluminium do?
What protects an alloy at high temperature is its oxide layer. The aluminium in 601 increases that layer’s adherence to the metal and prevents the scale spalling under heating and cooling cycles. Special Metals, Rolled Alloys, VDM Metals, NeoNickel, High Performance Alloys and Jacquet — six organisations — agree on this point: 601 forms a tight oxide scale that stays bonded to the metal even when repeatedly reheated.
The result is a concrete difference in continuous service temperature: the published figure for 601 is about 1200 °C (Special Metals 2200 °F, VDM 1200 °C, Rolled Alloys 2200 °F, NeoNickel 1204 °C). For 600 the sources scatter across 980 to 1093 °C (Special Metals 980 °C, Sandmeyer and Rolled Alloys 1093 °C); because they do not converge on one value, we give it as a range.
Compared in figures
The values are ASTM B166 / B168 composition limits.
| PROPERTY | Inconel 601 (N06601) | Inconel 600 (N06600) |
|---|---|---|
| Nickel (Ni) | 58.0 – 63.0 % | 72.0 % minimum |
| Chromium (Cr) | 21.0 – 25.0 % | 14.0 – 17.0 % |
| Aluminium (Al) | 1.0 – 1.7 % (addition) | not an alloying element |
| Iron (Fe) | balance | 6.0 – 10.0 % |
| Carbon (C) | 0.10 % max | 0.15 % max |
| Manganese (Mn) | 1.0 % max | 1.00 % max |
| Silicon (Si) | 0.50 % max | 0.50 % max |
| Sulphur (S) | 0.015 % max | 0.015 % max |
| Copper (Cu) | 1.0 % max | 0.50 % max |
| Continuous service temperature | approx. 1200 °C | 980 – 1093 °C (per source) |
| Defining property | oxidation + cyclic scale adherence | chloride SCC and caustic resistance |
Which one, where?
Inconel 601 is preferred for: heat treatment fixtures and baskets, radiant tubes, furnace components, refractory anchors, thermocouple protection tubes, steam superheater supports, rotary kilns, municipal waste incinerator combustion chambers, exhaust manifolds and thermal reactors, ammonia crackers, nitric acid catalyst grids. What they have in common is high temperature and thermal cycling.
Inconel 600 is preferred for: nuclear reactor components and high-purity water, caustic alkali (NaOH) production, dry chlorine and HCl service, vinyl chloride reactors, heat treatment muffles and retorts, vacuum furnace fixtures, food processing and electronic components.
Caution: where chloride stress corrosion cracking or caustic service is involved, moving to 601 is not an upgrade but a step backwards — its nickel has been reduced.
What to watch when ordering
“Inconel” is a registered trademark, not a generic word.
INCONEL® is a trademark of Special Metals Corporation. VDM Metals’ equivalent is Nicrofer 6023 H / VDM Alloy 601, Rolled Alloys’ is 601 Alloy. Write UNS N06601 / N06600 and ASTM B166 or B168 into your specification — writing “Inconel 601” may tie you to a single source.
A little-known process warning for 601
VDM Metals reports that 601 carries a risk of stress relaxation cracking during continuous operation above 100 hours in the 600–650 °C range, and recommends a heat treatment of about 3 hours at 980 °C as mitigation. That temperature band sits squarely in the middle of many waste heat and exhaust applications, and it does not appear on most datasheets.
Two further warnings: aluminium is not an alloying element in 600 — it is misleading when some suppliers publish an aluminium figure for it. And “typical” and “minimum” are frequently confused in the mechanical data; the gap can be a factor of two. Ask which one appears on the certificate.
Designations, standards and AMS equivalents
The same steel is called different things depending on which system you are speaking in. Most ordering and certification confusion starts here, so a short summary:
- AISI — the American Iron and Steel Institute’s grade naming (410, 316L and so on). It is the most widely used name in everyday use, but on its own it is not a purchasing specification: composition and mechanical requirements are defined in the ASTM standards.
- UNS — the Unified Numbering System operated jointly by ASTM and SAE (S41000 and so on). It is the number used for ordering and certification in North America, and it is more precise than the AISI name.
- W.Nr / EN — the European material number (1.4006 and so on) and EN name (X12Cr13 and so on). This is the governing designation in Europe. It is usually only an approximate equivalent of the AISI grade; carbon, sulphur or molybdenum limits frequently differ.
- AMS — SAE’s Aerospace Material Specifications. An AMS specification binds not only the composition but also the melting practice, the product form, the heat treatment condition and the inspection requirements. In aerospace and defence orders this is the designation that governs.
| DESIGNATION | Inconel 601 | Inconel 600 |
|---|---|---|
| AISI / trade name | Inconel 601 | Inconel 600 |
| EN material no. (W.Nr) | 2.4851 | 2.4816 |
| UNS number | N06601 | N06600 |
| AMS specifications | AMS 5870 | AMS 5540 · AMS 5665 |
| Product page | Inconel 601 technical page | Inconel 600 technical page |
Two reminders. First: an AMS number is specific to a product form and condition. The same grade may have separate AMS specifications for bar, sheet and forgings, so establish which product form you need before calling up an AMS number.
Second: the AISI name, material number, UNS and AMS data in the table above are the designations shown on Defence Metal’s product pages. If you are working to a different edition of a standard or to a different product form, state the material number and the specification edition explicitly on your order.