Is Hastelloy C276 the same as inconel C276?

No. And the reason is simpler than most answers to this question admit. There is no such grade as Inconel C276. The name is a search phrase that has been repeated often enough to look like a designation, and it describes an alloy that no mill produces and no standard lists.

What exists is Hastelloy C276, which is UNS N10276, a nickel-molybdenum-chromium alloy with tungsten. Inconel is a different family of alloys from a different company, built for a different set of problems. The two names are trademarks, not categories, and a trademark does not extend to an alloy that its owner does not make.

The distinction has a practical cost. A purchase order that asks for Inconel C276 can legitimately be answered with at least three different materials, and two of them are not C276. What follows sets out what the name means, what it does not mean, and how to write an order that cannot be answered with the wrong alloy.

The nickel industry grew up around a small number of trademarked families, and the names survived the companies that created them. Each one covers a metallurgical direction, and the direction is the useful part.

The trademark position matters for a buyer because it decides what a supplier is allowed to call a product. Hastelloy is a trademark of Haynes International, and Inconel is a trademark of Special Metals Corporation. Neither company lists a grade called C276 in the family of the other, because neither owns the name of the other.

In practice the trade has blurred the line in two directions. Distributors write Inconel C276 in catalogue headings because buyers search for it, and workshops say Hastelloy 718 for the same reason. The first is a marketing habit and the second is a mistake, and both are worth recognising when a quotation arrives with a trade name and no UNS number.

The alloy has a precise identity, and it is written in numbers and not in trade names. Those numbers are what a mill, a testing laboratory, and a pressure vessel inspector all read the same way.

The generic name in the third row is the one worth learning. NiMo16Cr15W says molybdenum first, at about 16 %, then chromium at about 15 %, then tungsten. That order is the character of the alloy: it is a molybdenum alloy that contains chromium, and that is why it survives hydrochloric acid and wet chlorine where a chromium-rich alloy does not.

Two of those levels explain most of the confusion in the market. The molybdenum at 16 % is roughly double what the common nickel-chromium-molybdenum alloys carry, and the tungsten is absent from most of them. An alloy without those two is not a cheaper C276. It is a different material with a different ceiling in chloride and reducing service.

When the phrase appears in an enquiry, it usually means one of three alloys, and the three are not interchangeable. Asking which one is meant takes one question and saves a rejected delivery.

Alloy 625 is the one that gets named most often and is the least similar to C276. Its molybdenum is about 9 %, roughly half, and its niobium is there for strength and not for corrosion. In chlorinated and reducing service the difference is visible: 625 is the better alloy in oxidising conditions and at temperature, and C276 is the better one in hydrochloric acid, wet chlorine, and chloride crevices.

Alloy 686 is the answer to a more interesting question. It is branded Inconel, it carries the same molybdenum and tungsten levels as C276, and it carries more chromium. If a buyer genuinely wants an Inconel-branded alloy for C276 service, 686 is the honest comparison, and it is not the grade most quotations offer.

The failure is quiet, and it usually surfaces at the receiving inspection and not at the enquiry. A certificate arrives with a UNS number that does not match the drawing, the buyer has no reference for the trade name, and the argument about who is responsible starts.

Four outcomes are possible, and only the first is correct. The supplier may recognise the phrase as C276 and deliver N10276, which is what the buyer wanted. The supplier may read Inconel as the governing word and quote 625, which is a legitimate alloy and the wrong one. The supplier may offer 686 on a price and availability basis. Or the buyer may receive a generic nickel-chromium-molybdenum alloy with a certificate that names no UNS number at all, which is the outcome that costs the most to resolve.

The cost of the mistake depends on the service. In an oxidising environment at temperature, 625 will often outperform C276 and the substitution is harmless. In hydrochloric acid, wet chlorine, or a chloride crevice, the loss of roughly seven points of molybdenum and the absence of tungsten is a real reduction in resistance, and the failure will appear as pitting or as crevice attack at a flange and not as a uniform loss of section.

There is also a paperwork consequence that matters to a fabricator. A pressure vessel or a piping system is qualified against a specification, and the specification names a UNS number. A certificate that carries a trade name and no number cannot be traced to the design, and a third party inspector will reject it on that basis alone, before any question of alloy performance arises.

The useful comparison is not with the Inconel family. It is within the C-type family, where each member trades one kind of resistance against another.

Read as a family, the table shows why no single grade is simply the best. Chromium buys oxidising resistance and molybdenum buys reducing resistance, and every C-type alloy sits somewhere between the two. C276 sits on the molybdenum side with enough chromium to be useful in air, and 686 moves the balance towards chromium without giving up the molybdenum.

Five items remove the ambiguity completely, and the first one does most of the work on its own.

The first item is the one to insist on. A trade name is a description of a family or a marketing phrase, and a UNS number is an identity. An order that carries N10276 cannot be filled with 625 by accident, because the certificate would show the wrong number and the receiving inspection would catch it.

DLX supplies C276 plate, sheet, bar, tube, and fittings from Changzhou, Jiangsu, with the UNS number, the product standard, and the heat treatment stated on the certificate. The same works cover 625 and 686 for the enquiries where the service is oxidising and not reducing, so the answer to a C-type question can include the alternatives and not only the grade that was named.

Two questions settle most of these enquiries. The first is the medium, because a reducing acid and an oxidising bleach point to opposite ends of the family. The second is the form and the standard, because the same alloy in plate and in welded tube carries different test requirements and a different certificate.

No. Inconel and Hastelloy are separate trademarks held by separate companies, and neither lists a grade called C276 in the other family. C276 is UNS N10276, a nickel-molybdenum-chromium alloy with tungsten, and the correct trade name is Hastelloy C276 or the generic alloy C276.

No. Both are nickel-chromium-molybdenum alloys and they differ in the numbers that matter. 625 carries about 9 % molybdenum and 3.65 % niobium, and C276 carries 16 % molybdenum and 3 to 4.5 % tungsten. 625 is stronger and better in oxidising conditions, and C276 is more resistant in reducing acids and in chloride crevices.

686, UNS N06686. It carries the same molybdenum range and the same tungsten addition as C276, with about 21 % chromium instead of 15 %, which improves the oxidising side of its performance. It is not interchangeable in a qualified design, and it is a far closer comparison than 625.

Not without approval. It is a different alloy with a different UNS number, and a design qualified against N10276 is not satisfied by N06625. In some oxidising services 625 performs better, and that is an engineering decision and not a purchasing one, and it needs a documented change.

Because buyers search for it. The phrase combines the family name that people recognise with the grade number they need, and a distributor who omits it loses the enquiry. The name is a search term and not a designation, and a quotation that relies on it without a UNS number is worth questioning.

2.4819, and the composition-based name is NiMo16Cr15W. The generic name is the most useful of the three because it states the alloying direction: molybdenum first, then chromium, then tungsten. That order explains why the alloy behaves the way it does in reducing and in oxidising media.

The question has a short answer and a useful one. Hastelloy C276 and Inconel C276 are not the same, because the second does not exist. There is one alloy, UNS N10276, and it belongs to the Hastelloy family by trademark and to the nickel-molybdenum-chromium family by chemistry.

The practical lesson is to buy by number. A trade name describes a direction and a marketing history, and a UNS number describes a material. An order that names N10276, the product standard, and the condition cannot be filled with 625, and that is the outcome the question is really about.

ASTM B575 for plate, sheet, and strip in the low-carbon nickel-chromium-molybdenum family, for the UNS N10276 chemistry and the flat product requirements.

ASTM B574 for rod and bar in the same family, for the bar product specification.

ASTM B622 and B626 for seamless and welded tube, with B619 covering welded pipe.

ASTM B366, factory-made wrought nickel and nickel alloy fittings, for the fitting specification.

Haynes International, HASTELLOY C-276 alloy data sheet, for the composition, the solution annealing treatment, and the corrosion data behind the C-type comparison.

Special Metals Corporation, INCONEL alloy 625 and alloy 686 technical bulletins, for the composition of both grades and the chromium, molybdenum, and tungsten levels quoted.

ASTM G28 and G48, for the intergranular corrosion and the pitting and crevice corrosion tests named in the ordering section.

The composition ranges quoted are the standard limits and a mill certificate reports the actual analysis of the heat, which will sit inside them. The trade names are used descriptively, and the trademarks belong to their respective owners. The comparison between C276, 625, and 686 is a statement about composition and about the general direction of corrosion resistance, and it is not a ranking for a specific medium; selection for a real service depends on concentration, temperature, and aeration, together with the presence of crevices. The product standards named apply to the forms listed, and a bar, a plate, and a welded tube of the same alloy carry different tests. Standards are revised, and the edition named on the order governs. Nothing here is a substitute for an engineering release or for a corrosion assessment of the actual process.