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Inconel 600 / (2.4816) / UNS N06600 / AMS 5540 / AMS 5665

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Inconel 600 (2.4816), also widely known as Alloy 600, is one of the most widely used of all nickel alloys. The material contains essentially more than 70% nickel. Containing close to 15% chromium alongside the nickel, this high-nickel alloy is one of the most readily available nickel alloys. Designated 2.4816 in the DIN system, its EN designation is NiCr15Fe.

Best described as an engineering material, it is frequently chosen where high temperatures are involved and where high corrosion resistance is required at the same time. Thanks to the high nickel content, the material withstands many acids and demanding environments. This nickel alloy cannot be hardened by ageing: age hardening is possible with Inconel 718, for example, but not with this material, which can only be hardened by cold work. Able to operate even at high temperatures, it can be used in parts working at temperatures as extreme as 1095 °C.​‌​​‌​

One of the most frequent application areas for Inconel 600 is the chemical industry. It is used in parts requiring high mechanical properties together with high corrosion resistance. Various industrial heaters, piping carrying acids, and environments where pressure and temperature occur together are among its most common applications. Also used in many furnace components in heat treatment furnaces, Alloy 600 is likewise used in many engine parts that must withstand high temperatures. As with many Inconel materials, Alloy 600 is also widely used in nuclear reactors.

Standards by Product Form​‌​​‌​

Inconel 600 (UNS N06600 / W.Nr. 2.4816) is the 72 % minimum nickel Ni-Cr-Fe alloy. The most expensive mistake on this page is a single standard number: alloy 600 does not have “an ASTM standard” — it has a different one for every product form, plus two classes of document that look alike but are not.​‌​​‌​

Watch the general-requirements specifications. B906, B829, B775 and B751 are general-requirements standards; each states in its own text that where it conflicts with the product specification, the product specification governs. A purchase order citing only “ASTM B829” has specified nothing about the material. Equally, a stockist’s short specification list is not the alloy’s specification list — absence of a form from that list is not absence of the form from the standard.​‌​​‌​

Composition: Ni (+Co) ≥72.0 % · Cr 14.0–17.0 % · Fe 6.00–10.00 % · C ≤0.15 % · Mn ≤1.00 % · Si ≤0.50 % · Cu ≤0.50 % · S ≤0.015 %. Note the nickel line: the limit is on Ni + Co combined, not nickel alone, so mill certificates reporting the two separately need adding before comparison. Carbon circulates as three different figures: ASTM and the originator give 0.15 % max; aerospace and wire practice quotes 0.10 % max; one mill datasheet footnotes 0.20 %, contradicting its own table. Specify your limit on the order.

Toughness and creep: Charpy keyhole on ½-in plate gives 82–86 J at 21 °C, 88–91 J at −79 °C and 82–83 J at −196 °C — there is no ductile-to-brittle transition. Against that, the 100,000-hour rupture stress is 110.3 MPa at 538 °C but only 8.3 MPa at 871 °C. Read the two together: the alloy is excellent cryogenically and is not load-bearing above about 800 °C.

Welding and Heat Treatment​‌​​‌​

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Welding

Processes: GTAW, GMAW, SMAW and SAW. Filler: Filler Metal 82 (AWS ERNiCr-3) for gas-shielded processes, Electrode 182 (AWS ENiCrFe-3) for SMAW. No numeric heat input, interpass temperature or preheat is published on this page — none of the sources reviewed publishes figures, and the binding values come from welding-procedure qualification. No post-weld heat treatment is required for mechanical reasons; a stress relief is mandatory only for caustic service (below).​‌​​‌​

Two real traps in welding. First, sulphur is catastrophic. The material must be clean before it is heated and must be heated in a sulphur-free atmosphere; no MoS₂ lubricant above 427 °C; sulphurised cutting fluids must be completely removed before welding or heat treatment. At 72 % Ni the alloy forms a low-melting nickel-sulphide eutectic. Second, the weld metal does not share the base metal’s service envelope — the originator states that welds made with Electrode 182 may have decreased ductility after extended exposure at 540–760 °C, in the same document in which it says the base metal shows no embrittlement after prolonged high-temperature exposure. The joint, not the plate, is the limiting element.

Heat treatment​‌​​‌​

Not hardenable by heat treatment — hardened only by cold work; there is no ageing response. Standard anneal ~1010 °C (1850 °F) for about 15 minutes; softening begins around 871 °C and is largely complete after 10–15 minutes at 982 °C. For maximum creep resistance, solution treat at 1090–1150 °C for 1–2 hours (dissolving carbides and coarsening the grain). Do not conflate the two bands: chromium carbides precipitate between 540 and 980 °C, but the material is made sensitised — open to intergranular attack — by exposure between 540 and 760 °C. Quoting the wider band as the sensitisation window over-restricts fabrication; quoting the narrower one as the precipitation range understates the risk. Hence the requirement to cool rapidly through 540–760 °C.

Stress relief for caustic service — sources diverge: the originator gives 900 °C/1 h or 790 °C/4 h; two distributors give 900 °C/1 h minimum, 980–1010 °C/1 h preferred. The common ground is 900 °C/1 h; note that 790 °C sits just above the top of the sensitisation band.​‌​​‌​

Machining, Forming and Service Limits

Machinability is slightly better than Type 304 and slightly worse than free-machining Type 303. Cutting speeds: 11–14 m/min with high-speed-steel tooling, 30–53 m/min with carbide (single-sourced). Heavy-duty equipment is needed, with tools large and heavy enough to carry the load and dissipate heat quickly, and kept sharp. The work-hardening rate is higher than mild steel but lower than Type 304 stainless — the opposite of the common assumption. Hot working 870–1230 °C; heavy work 1040–1230 °C. Do not work between 650 and 870 °C (low ductility). One source puts the top of the range at 1260 °C; the divergence is worth knowing.​‌​​‌​

Sources diverge on density and modulus; do not average them. Density: 8.47 g/cm³ (the originator and one wire producer) or 8.42–8.43 g/cm³ (three distributors). Young’s modulus: 214 GPa (originator) or 207 GPa (four sources). Poisson’s ratio 0.324 or 0.29. Thermal expansion over 20–100 °C is 13.3 µm/m·°C — appreciably below austenitic stainless (≈16–17), which matters at tube-to-tubesheet joints and in dissimilar-metal welds.​‌​​‌​

Frequently Asked Questions

Inconel 600, 601 or 690 — when is each actually required?​‌​​‌​

These are not grades of one alloy; they are three chemistries solving three problems, and each substitution fails in a specific, predictable way. 600 is Ni ≥72 %, Cr 14–17 %, with no aluminium. Its selling point is the nickel: virtually immune to chloride stress-corrosion cracking, good carburisation resistance, and dry chlorine and HCl gas service to about 538 °C. 601 is Ni 58–63 %, Cr 21–25 % and — the whole point of the alloy — Al 1.0–1.7 %. That aluminium builds a tightly adherent scale that resists spalling under thermal cycling. Substitute 600 for 601 and in cyclically heated oxidising service the chromia scale spalls, fresh metal is exposed, and the part loses section by repeated re-scaling. The reverse substitution costs you nickel and therefore chloride-SCC margin. 690 is Cr 27–31 %, C ≤0.05 %, and it exists precisely because 600 cracks by PWSCC in high-temperature primary water; it also gives <1 mpy in nitric acid through 70 %. Substitute 600 for 690 and you get stress-corrosion cracking in nuclear primary water or rapid attack in oxidising acid — a functional failure, not a saving.

Should we order “600H” for high-temperature service? What do carbon and grain size mean here?​‌​​‌​

There is no 600H. The UNS lists in B168, B166, B167 and B564 contain N06600 and no H variant. The habit comes from Incoloy 800H/800HT, where controlled carbon and grain size are written into the specification. For alloy 600 they are not — so if you need them, they must be written onto the purchase order as supplementary requirements. This matters because the alloy pulls in two directions. The originator specifies a solution treatment at 1090–1150 °C for 1–2 hours to dissolve carbides and coarsen grain, maximising creep resistance — the right move for a furnace retort. But chromium carbides precipitate between 540 and 980 °C, and exposure between 540 and 760 °C leaves the material sensitised and open to intergranular attack in aggressive aqueous media, which is why rapid cooling through that band is required. The heat treatment that buys creep life is the opposite of the one that protects an aqueous-service part, and a weld HAZ passes through the sensitisation band whatever you do. Carbon itself is disputed: ASTM permits 0.15 % max, aerospace and wire practice quotes 0.10 % max, and at least one mill datasheet prints 0.20 %. State your limit explicitly.

Which standard goes on the purchase order?​‌​​‌​

Alloy 600 does not have “an ASTM standard”. It has a different one for every product form, and two classes of document that look alike. Material specifications, one per form: B168 plate, sheet and strip; B166 rod, bar and cold-worked wire; B564 forgings; B167 seamless pipe and tube; B163 seamless condenser and heat-exchanger tube (scope limited to 76.2 mm OD and below); B516 welded tube (1/8–5 in OD); B517 welded pipe, made autogenously without filler; B366 wrought fittings. ASME’s SB-prefixed twins are the Code versions of the same documents. General-requirements specifications cannot be ordered alone: B906 flat-rolled, B829 seamless pipe and tube, B775 welded pipe, B751 welded tube — each states that where it conflicts with the product specification, the product specification wins. Two specific traps: B168 is plate, sheet and strip only and is routinely mis-cited as covering pipe; and a distributor’s specification list is not the alloy’s — a stockist lists only the forms it stocks.

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