Hastelloy Material Grades Explained: C276, C22, B3 and X

Most engineers who specify Hastelloy default to C276. It is familiar, widely stocked, and it usually works.

“Usually works” is an expensive standard when the alloy costs several times the price of 316L. In strongly oxidising service, C22 delivers materially longer life. In pure reducing acid, B3 outperforms both. And in high-temperature service, neither C-series grade is the right answer at all.

This guide covers the Hastelloy material grades that matter in practice — what each is composed of, which corrosive environment it was designed for, and how to avoid the substitution errors that cause premature failure.

Asiad Steel Industries supplies Hastelloy and other nickel alloys in fittings, flanges, fasteners and raw material from our Pune facility, serving chemical processing, pharmaceutical, oil and gas and pollution control projects.

What Is Hastelloy?

Hastelloy is a family of nickel-based superalloys engineered for extreme corrosion resistance in environments where stainless steel fails. The main grades are C276 and C22 (nickel-chromium-molybdenum, for broad corrosion resistance), B3 (nickel-molybdenum, for reducing acids) and X (for high-temperature service). Hastelloy is a registered trademark of Haynes International.

That trademark point has a practical consequence for procurement. Only Haynes International products can legally carry the Hastelloy name. Other mills produce chemically identical material under different trade names — “alloy 22”, “alloy C276” and so on.

This is why the UNS number matters more than the brand name. The Unified Numbering System designation is the universal reference:

Always specify and verify the UNS number alongside the applicable ASTM standard. Cross-referencing errors between mills are a genuine source of substitution problems.

The Hastelloy Grade Families

The letter-number designations reflect development sequence, not composition, which is why they look arbitrary:

C276 and C22 together account for the substantial majority of Hastelloy consumed globally, which is why most technical discussion focuses on those two.

Hastelloy C276 (UNS N10276)

The workhorse of the family and the most widely stocked grade.

Nominal composition: approximately 57% nickel, 16% molybdenum, 16% chromium, 5% iron, with tungsten, cobalt and manganese in smaller amounts.

Strengths:

• Outstanding resistance to pitting, crevice corrosion and stress corrosion cracking
• Performs in both oxidising and reducing environments — the versatility that makes it the default choice
• Excellent in wet chlorine, hypochlorite and chloride-contaminated media
• Well understood, widely available, extensive service history

Best for: chemical processing, flue gas desulphurisation, pulp and paper bleaching, pharmaceutical reactors, waste treatment, and any application where the corrosive media varies or is not fully characterised.

Where it is not optimal: strongly oxidising acids and mixed acid conditions, where C22 performs better.

Hastelloy C22 (UNS N06022)

Nominal composition: approximately 56% nickel, 22% chromium, 13% molybdenum, 3% iron, 3% tungsten, with cobalt limited to 2.5% maximum.

The higher chromium content relative to C276 is what drives the performance difference.

Strengths:

• Superior to C276 in oxidising acid environments
• Better performance in mixed acid conditions
• Excellent resistance to localised corrosion and weld attack

Best for: oxidising acid service, mixed acid streams, nitric and sulphuric acid mixtures, and applications where C276 has shown accelerated attack.

Where C276 is preferable: strongly reducing environments, and cost-sensitive projects where C276’s performance is adequate.

C276 vs C22 — the decision

The most common specification error we see is defaulting to C276 out of familiarity without assessing whether C22 would deliver meaningfully longer service life for the specific media.

Hastelloy B3 (UNS N10675)

Compositionally very different from the C-series. B3 is essentially a nickel-molybdenum alloy with minimal chromium, optimised purely for reducing acid service.

Strengths:

• Exceptional resistance to hydrochloric acid at all concentrations and temperatures
• Excellent in hydrogen chloride gas, sulphuric acid and acetic acid
• B3 offers improved thermal stability over the older B2

Critical limitation: B-series alloys have very low chromium content and are not suitable for oxidising conditions. Introducing ferric or cupric ions, or oxidising contaminants, into an HCl stream running in B3 will cause rapid attack. This is the failure mode to guard against.

Best for: hydrochloric acid processing, HCl gas handling, and reducing acid service where oxidising contaminants can be reliably excluded.

Hastelloy X (UNS N06002)

Nominal composition: approximately 47% nickel, 22% chromium, 18% iron, 9% molybdenum, 1.5% cobalt, with tungsten.

A high-temperature alloy dating from the 1950s and still widely used. It offers a good balance of high-temperature strength and oxidation resistance, and cannot be strengthened by heat treatment.

Best for: gas turbine components, furnace parts, combustion chambers, industrial heating equipment and petrochemical furnace applications.

Note: X is selected for temperature performance, not aqueous corrosion resistance. Do not substitute it for a C-series grade in acid service.

Hastelloy vs Stainless Steel: When to Upgrade

The economics matter, because nickel alloys cost several times commodity stainless.

The upgrade is justified when the failure cost — unplanned shutdown, product contamination, safety exposure — exceeds the material cost differential. In a continuous chemical plant, one avoided shutdown typically pays for the alloy several times over.

Where Hastelloy is genuinely overspecified is in applications a duplex grade would handle. Assess duplex before jumping from 316L to a nickel alloy.

Fabrication and Procurement Notes

• Machinability: Hastelloy work-hardens rapidly. Slow speeds, positive feed and rigid setups are essential. Machining costs are materially higher than stainless.
• Welding: generally good weldability, but heat input must be controlled. Matching filler metal is standard practice.
• Heat treatment: solution annealing restores corrosion resistance after significant cold work or welding.
• Documentation: insist on full chemical analysis per heat, plus EN 10204 3.1 mill test certificates. Verify the UNS number on the certificate, not just the trade name on the invoice.
• Product forms: available as plate, sheet, bar, pipe, tube, fittings, flanges and fasteners.

Explore our Hastelloy range, and related nickel alloys Inconel, Monel, Nickel and Titanium.

Conclusion

Selecting between Hastelloy material grades comes down to characterising the environment honestly:

• Oxidising acids or mixed acid streams → C22
• Reducing acids, wet chlorine, variable media → C276
• Pure hydrochloric acid without oxidising contaminants → B3
• High temperature with oxidation exposure → X
• Verify the UNS number, not the trade name, on every certificate

The default to C276 is defensible when media are variable or poorly characterised. It is not defensible when a specific, well-understood oxidising environment would be better served by C22, or when duplex stainless would have done the job at a fraction of the cost.

Asiad Steel Industries supplies Hastelloy and nickel alloy components — fittings, flanges, fasteners and raw material — from Pune, with full chemical analysis and mill test certification traceable to heat number. We manufacture custom components to drawing where standard product forms do not fit.

Specifying a nickel alloy? Send us your service conditions — media, concentration, temperature and contaminants — and our technical team will recommend the appropriate grade before quoting.

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FAQs

What are the main Hastelloy grades?

The commercially significant grades are C276 (UNS N10276) and C22 (UNS N06022) for broad corrosion resistance, B3 (UNS N10675) for reducing acids, and X (UNS N06002) for high-temperature service. The C-series are nickel-chromium-molybdenum alloys, the B-series are nickel-molybdenum, and X is a high-temperature nickel-chromium-iron-molybdenum alloy. C276 and C22 account for most global consumption.

What is the difference between Hastelloy C276 and C22?

C22 contains higher chromium (approximately 22% versus 16%) and performs better in oxidising acid environments and mixed acid conditions. C276 contains more molybdenum and performs better in strongly reducing environments, and is more widely stocked and generally more economical. For variable or poorly characterised media, C276 offers greater versatility.

Is Hastelloy better than stainless steel?

For severe corrosion service, yes — but the comparison is application-specific. Hastelloy resists strong acids, wet chlorine and aggressive chlorides that would rapidly attack 304 or 316. However it costs several times more and is harder to machine. For moderate chloride exposure, SS 316L or a duplex grade is often the correct and far more economical choice. Assess duplex before upgrading to a nickel alloy.

Can Hastelloy B3 be used in oxidising environments?

No. B-series alloys contain very little chromium and are designed exclusively for reducing conditions such as hydrochloric acid. Oxidising contaminants — ferric or cupric ions, or dissolved oxidants — cause rapid attack. If an HCl stream may contain oxidising species, specify a C-series grade instead.

Why is the UNS number important when ordering Hastelloy?

Hastelloy is a registered trademark of Haynes International, so only their material carries the name. Other mills supply chemically identical alloy under different trade names such as “alloy 22”. The UNS designation — N10276 for C276, N06022 for C22 — is the universal identifier and should be verified on the mill test certificate. Relying on trade names alone risks cross-referencing errors and substitution.

What documentation should I request with Hastelloy?

Request EN 10204 3.1 mill test certificates with full chemical analysis per heat, the UNS number stated explicitly, and the applicable ASTM specification. For critical service, corrosion testing on the incoming heat may also be justified. Verify that the certificate UNS number matches your specification rather than accepting a trade name on the invoice.