Hastelloy C-276 / (2.4819) / UNS N10276 / AMS 5530 / AMS 5750
Hastelloy C-276 was developed around fifty years ago to withstand various acids and many demanding environments, and its use is becoming increasingly widespread today. Designated UNS N10276 in the UNS system, the material carries the material number 2.4819.
Alloy C-276 was produced and developed to have excellent corrosion resistance in very demanding and aggressive environments. With its high nickel and molybdenum content, the material preserves its durability over long periods in a wide variety of corrosive environments. The roughly 15% molybdenum in the material in particular raises its resistance to pitting corrosion. This nickel alloy contains very little carbon: its carbon content is below 0.01%, and that low carbon content allows the material to be welded more readily. With low carbon, carburisation during welding is minimised, so there is no loss of corrosion resistance or of mechanical properties in the welded areas. Alloy C-276 also contains a significant proportion of tungsten.
Hastelloy C-276, also widely known as Inconel Alloy C-276, is used in many areas where chemical reactions take place. It is a nickel alloy also frequently used in various special filters, in parts in contact with pulp in paper production, in paper manufacture, in the storage of industrial waste, in certain parts in contact with natural gas, in special fan components, in heat exchangers, in special vessels and tanks in which many chemical reactions take place, and in liquid evaporation systems and the pipework of those systems.
What Hastelloy C-276 Is — and the Honest C-276 / C-22 / C-2000 Positioning
Hastelloy C-276 (UNS N10276 / W.Nr. 2.4819 / DIN NiMo16Cr15W / ISO NiMo16Cr15Fe6W4) is a wrought, single-phase face-centred-cubic (austenitic) nickel–chromium–molybdenum–tungsten solid-solution alloy: nominally ~57 Ni – 16 Cr – 16 Mo – 4 W – 5 Fe. It is not precipitation-hardenable; it can be strengthened only by cold work. Every other Ni-Cr-Mo grade is effectively benchmarked against it — it is the industry reference alloy.
Trade names: HASTELLOY® C-276 (Haynes International, trademark owner), INCONEL® alloy C-276, VDM® Alloy C-276 / Nicrofer 5716 hMoW, generic “Alloy C-276”. Composition standard: DIN 17744:2020-12 (current; replaces 2002-09) · ISO/TR 15608 group 43.
WARNING — the filler metal has its own number: base metal 2.4819, bare welding wire 2.4886 (SG-NiMo16Cr16W), covered electrode 2.4887 (EL-NiMo15Cr15W).
The chemistry is a deliberate compromise. Mo (15.0–17.0 %) and W (3.0–4.5 %) carry resistance to reducing acids (HCl, H₂SO₄) and are the main contributors to pitting and crevice resistance. Cr (14.5–16.5 %) carries resistance to oxidising media — and at only ~16 % this is the alloy’s principal weakness. Fe 4.0–7.0 % is a deliberate specified range, not a residual.
The single most important fact: low C and low Si → usable AS WELDED
The predecessor, alloy C (1930s), carried much higher carbon and silicon. On heating through roughly 600–1100 °C — exactly the cycle a weld heat-affected zone experiences — it threw brittle, Mo-rich intergranular precipitates at grain boundaries, depleting the adjacent matrix of Mo and Cr. The consequence was commercially ruinous: every welded fabrication destined for corrosive service had to be re-solution-annealed after welding — for a large vessel or a field weld, either prohibitively expensive or physically impossible. C-276 (1960s) was made possible by argon-oxygen decarburisation (AOD), which allowed carbon and silicon to be driven down to residual levels. This is the alloy’s entire reason for existing.
Carbon 0.010 % max (100 ppm). Carbon forms M₆C carbide at grain boundaries. The mill’s metallurgy guide calls M₆C “the most important second phase resulting from residual (unwanted) elements” and states it forms “even at very low residual carbon levels (0.005 wt.% or less)” — with kinetics faster than sigma. 0.010 % does not eliminate carbide precipitation; it slows it enough that a weld thermal cycle cannot produce a continuous grain-boundary film.
Silicon 0.08 % max. Silicon is a deoxidiser residual that strongly promotes intergranular precipitation. The mill: carbon and silicon “are undesirable residuals… they precipitate deleteriously at grain boundaries during hot working and welding if present in excess“.
The operative design statement: the alloy is formulated so that “short-term thermal excursions above 500 °C (as encountered during welding) do not cause continuous precipitation“. Three independent publishers corroborate: the alloy “has resisted the formation of grain boundary precipitates in the weld heat-affected zone“, enabling use “in the as-welded condition in most chemical and petrochemical process equipment“.
But do not over-read this. “As-welded” means no mandatory PWHT. It does NOT mean the alloy is indifferent to time at temperature. Nor does it mean weld metal equals base metal: the mill’s own all-weld-metal data show weld rates consistently above base metal — 70 % H₂SO₄ at 66 °C: weld 0.13 mm/y vs base metal 0.05 mm/y.
C-276 · C-22 · C-2000 — where distributor pages mislead most
These three are NOT a quality ladder; they are a Cr/Mo trade-off. There is no answer to “which is best”; there is an answer to “is the environment oxidising or reducing”.
Buying rule: if the service is reducing or mixed → C-276. If it is oxidising or oxidising-chloride → moving to C-22 / 59 / 686 is a genuine upgrade, not marketing. If it is nitric or strongly oxidising → none of the C family is the right answer. Sister alloys: C-2000 · B-3 · Inconel 625 · Incoloy 825.
Standards by Product Form
ASTM B575 covers N10276 alongside N06022, N06035, N06058, N06059, N06200, N06210, N06455 and N06686; B574 covers N10276, N06022, N06035, N06059, N06455 and N06686. Practical warning: “certified to ASTM B575” alone does not tell you which alloy you received — look for the UNS number on the certificate.
Welding consumables — the most common catalogue error lives here. Bare rod/wire (GTAW, GMAW, SAW, plasma): AWS A5.14 / SFA-5.14 · ERNiCrMo-4 · UNS N10276 · W.Nr. 2.4886. Covered electrode (SMAW): AWS A5.11 / SFA-5.11 · ENiCrMo-4 · UNS W80276 · W.Nr. 2.4887.
Note the UNS asymmetry: the bare wire shares the base-metal UNS (N10276); the covered electrode has its own W-prefixed number (W80276). Any catalogue printing “ENiCrMo-4, UNS N10276” is wrong — and this is the single most common error in distributor catalogues. Over-alloyed options: 686CPT (ERNiCrMo-14/ENiCrMo-14 class), FM 59 (2.4607, ERNiCrMo-13). The welding-metallurgy literature states explicitly that for C-276 joints matching ERNiCrMo-4 is superior to ERNiCrMo-3 (alloy 625 filler).
The European / German route. DIN product standards: plate/sheet 17750 (ISO 6208), pipe/tube 17751 (ISO 6207), bar 17752 (ISO 9723/9724/9725), wire 17753, forgings 17754. VdTÜV-Werkstoffblatt 400, maximum design temperature 450 °C (844 °F) — the VdTÜV 400 strength table terminates at 450 °C. There is NO dedicated EN product standard: no EN equivalent of B575/B574 was found; European mills certify to DIN 17744 / 17750–17754 plus VdTÜV 400. This absence is inferred, not confirmed — do not write it as an absolute.
ASME Section IX: base metal P-No. 43, filler F-No. 43 — from two secondary sources; verify against QW-422/QW-432. A-Numbers DO NOT APPLY: ASME IX A-Numbers (QW-442) classify ferrous weld-metal chemistry only; any source quoting “A-No. N10276” is in error.
ASME Code Acceptance and MAXIMUM CODE TEMPERATURES
What follows are CODE LIMITS. They are not capability statements and they are emphatically not corrosion-service recommendations.
NOW THE MOST IMPORTANT SENTENCE ON THIS PAGE. The 677 °C that ASME VIII Div. 1 permits and the temperature at which the alloy is metallurgically viable are not the same thing. The mill’s own metallurgy guide states that C-276’s microstructure is metastable only from room temperature to approximately 427 °C, and that “long-term exposures reveal their equilibrium, multiple phase nature“; an independent comparison likewise cites 427 °C as the practical upper operating temperature. Code ceiling 677 °C; practical corrosion-service ceiling ≈425 °C. These are different numbers answering different questions. A vessel run continuously at 600 °C is code-legal and metallurgically doomed.
Product Forms With NO Standard — the Commercially Valuable Section
This is the section your sales engineers should memorise.
1. Wire (cold-drawn, spring, mesh). No ASTM or ASME product specification exists for N10276 wire. Three separate mill and distributor specification lists map wire only to DIN 17753 / ISO 9723-9725. Specify chemistry by reference to B574/B575 and mechanicals by agreement. Never write “ASTM B574 wire” — no such thing exists.
2. Bolting above 76 mm (3 in.) diameter. F468 explicitly states that mechanical properties of larger sections “shall be negotiated“. There is no code-covered, high-strength C-276 bolting above 3 in.
3. Castings. There is no ASTM casting specification with a C-276 composition. The cast equivalents (A494 CW-12MW, CW-6M) are different alloys with different chemistry and properties. A CW-12MW valve body is not “cast C-276”.
4. Cold-worked (non-annealed) sheet and strip tempers. B575 covers solution-annealed only; cold-rolled tempers are by mill agreement.
5. B626, B366, B462 and B564 mechanical minima. Assumed identical to B574/B575 but not independently verified — for a critical calculation, confirm against the standard.
6. Other fasteners. Washers, threaded rod and socket products outside the F468 scope — by agreement.
Chemical Composition
Why the tungsten is there. W is a specified range, not a tramp element. It behaves metallurgically like molybdenum (roughly half the potency per weight percent) and reinforces resistance to reducing acids and to pitting. The mill says it directly: alloy C-4 “contains 16 wt.% molybdenum and chromium with no tungsten“; C-276 adds 4 % W “for enhanced reducing acid resistance“. In nickel-alloy PREN formulations W is usually counted at half weight.
C ≤0.010 % and Si ≤0.08 % are hard specification limits, not typical values. A certificate showing C = 0.015 % is NON-CONFORMING to ASTM B575/B574. Check the carbon on every certificate: two major publishers print carbon as “0.02 % max” on their own C-276 data sheets — and 0.02 % carbon is precisely the condition C-276 was invented to eliminate.
The ASTM–DIN P/S divergence — real and commercially decisive
Phosphorus max: ASTM 0.04 % · DIN / VdTÜV 400: 0.025 % · VDM® (mill-internal): 0.02 % → a heat at P = 0.030 % passes ASTM and FAILS DIN 17744 / VdTÜV 400.
Sulphur max: ASTM 0.03 % · DIN / VdTÜV 400: 0.010 % · VDM®: 0.01 % → ASTM allows THREE TIMES the DIN sulphur. And sulphur is one of the impurity elements the mill names as driving weld solidification cracking.
Other narrowings: Cr min ASTM 14.5 % / VDM® 15.0 % · V max ASTM 0.35 % / VDM® 0.30 % · Ni ASTM “remainder” / VDM® 51.0–63.0 % as an explicit range.
Procurement implication: a certificate stamped “ASTM B575 / SB-575” does NOT automatically satisfy a European purchaser buying to DIN 17744 / VdTÜV 400. For dual-certified material, state P ≤0.020 % and S ≤0.010 % explicitly on the purchase order — do not assume it.
Mechanical Properties
Three concepts are kept rigidly apart here: the specification minimum (what you can legally rely on), the typical mill value (what a real heat usually tests at — never quote it as a guaranteed minimum on a quotation) and mechanical capability (what the metal can actually do). Confusing these three is the most common source of datasheet errors.
Explain the ASTM–EN gap to your customer. ASTM demands only 283 MPa / 690 MPa / 40 %; VdTÜV demands 310 MPa / 730 MPa but only 30 % elongation on thin sheet. Neither set dominates the other: material can pass ASTM and fail VdTÜV on yield, or pass VdTÜV and fail ASTM on elongation.
Physical Properties
Direct design consequences. 1) Thermal conductivity is roughly one-third that of carbon steel; size heat-exchanger surface area accordingly — do not carry over a carbon-steel or copper-alloy thermal design. 2) CTE ≈11–12 × 10⁻⁶/K sits between ferritic steel (~12) and austenitic stainless (~16–17); dissimilar-metal joints to 316L/304 will see differential expansion. 3) Resistivity is ~7× that of carbon steel and almost independent of temperature to 1000 °C. 4) It is non-magnetic — MAGNETIC PARTICLE INSPECTION CANNOT BE USED; dye penetrant, radiography or ultrasonics only.
Heat Treatment and Thermal Stability
This section is the metallurgical core of the page. All of C-276’s corrosion resistance depends on the alloying elements staying in solid solution. Every Mo and W atom that precipitates at a grain boundary does not merely create a brittle phase — it depletes the adjacent matrix of the very elements that provide the corrosion resistance. That is the sole purpose of the solution anneal and the rapid quench.
What happens on slow cooling — four steps. 1) M₆C nucleates on grain boundaries — it is fast, and it happens even at 50 ppm carbon. 2) Mo and W partition into the precipitates, leaving a depleted zone in the adjacent matrix. 3) That depleted zone is the failure path: intergranular corrosion and intergranular SCC — one mill states plainly that grain-boundary carbide precipitation “reduces intergranular corrosion resistance“. 4) With longer exposure μ and P phases EMBRITTLE the material. This is exactly why the 677 °C code ceiling must not be read as a service recommendation.
Hot working. The mill: start 1232 °C, finish 954 °C; “moderate reductions and frequent re-heating provide the best results“. Another mill: 870–1230 °C with all heavy forming above 1090 °C; others 950–1200 and 950–1230 °C; a specialty producer heats uniformly to 1204 °C for forging. Consensus: hot work between ~950 and ~1230 °C, finish above ~950 °C, then re-solution-anneal and quench.
Cold working. Start from the solution-annealed condition. The alloy work-hardens faster than austenitic stainless steel and is stiffer; more press force and more power are required than for 316L of the same section — size press tonnage accordingly, a routine cause of under-specified brake presses.
Re-anneal threshold — two figures, two purposes. The mill: re-anneal after ≥7 % outer-fibre elongation “for optimum stress corrosion cracking resistance“. Three European sources: after >15 % cold deformation. They are not contradictory: 7 % is the conservative SCC-driven trigger, 15 % the ductility-recovery trigger. For sour or chloride-SCC service, use 7 %.
Welding
Suitable processes: GTAW/TIG (including pulsed current, which measurably reduces Mo microsegregation at subgrain boundaries compared with conventional GTAW), GMAW/MIG (pulsed spray strongly preferred), SMAW, plasma arc, laser, electron beam, resistance welding.
FORBIDDEN: oxy-acetylene welding — carburisation risk, it destroys the low-carbon design; air carbon-arc gouging or cutting — carbon pick-up from the electrode. For cutting use plasma, waterjet or laser.
Filler metal: GTAW/GMAW/plasma/SAW ERNiCrMo-4 (A5.14, UNS N10276); SMAW ENiCrMo-4 (A5.11, UNS W80276). Matching filler is superior to ERNiCrMo-3 (alloy 625 filler). Where extra corrosion margin in the as-cast deposit is wanted: 686CPT or FM 59 / ERNiCrMo-13.
Stress relief at 620–650 °C is FORBIDDEN
C-276 is solid-solution strengthened, not precipitation-hardened. The mill: “Under the vast majority of service environments, corrosion-resistant alloys… are used in the as-welded condition, and post-weld heat-treatment of these alloys is generally not required.” But the real point is this: conventional stress relief is actively harmful. The mill’s C-276 welding data page: “Post-weld stress relieving in the 1200 °F (650 °C) range is NOT recommended.” Its welding brochure gives the reason: intermediate-temperature stress relief at 540–815 °C causes “precipitation of secondary phases in the microstructure which can have a detrimental effect on material properties, such as corrosion resistance“. Another producer: “Stress relief heat treatments are not effective” — use a full anneal instead. The controlling reaction is M₆C carbide, which forms between 650 and 1038 °C and does so even at 0.005 % carbon; molybdenum partitions into it, leaving a depleted, corrosion-prone boundary. A 620 °C soak is not a short excursion; it sits inside the precipitation window. The only acceptable PWHT is a full solution anneal at ~1100–1160 °C with a rapid quench. If a code or customer specification calls for “PWHT at 620 °C” by reflex from carbon-steel practice, that requirement must be challenged IN WRITING.
What actually goes wrong
1. Hot (solidification) cracking. Three conditions must coincide: liquid grain-boundary films, tensile stress on the solidifying weld, and impurity elements — specifically sulphur and phosphorus. The C-276-specific mechanism: microsegregation during fusion-zone solidification concentrates Mo and W and precipitates TCP P and μ phases. Controls: low heat input; convex, not concave, bead profile (“large concave weld beads that place the weld surface in tension tend to promote solidification cracking“); avoid fast travel that produces a teardrop-shaped weld pool; grind out all starts and stops (both Ni- and Co-base alloys have a marked tendency to crater-crack); and buy to the DIN/VDM S ≤0.010 % rather than the ASTM S ≤0.03 %.
2. The unmixed zone. In any nickel-alloy weld there is a thin layer of base metal that melted but did not mix with filler; it re-solidifies as-cast and segregated and is a preferential corrosion path. In corrosion service, avoid autogenous (no-filler) welds. No quantitative data for C-276 was found — do not publish a number.
3. Dilution from carbon steel. Where C-276 is welded to, or overlaid on, carbon or low-alloy steel, iron dilution reduces the effective Ni, Cr and Mo of the deposit. This is why overlay practice is a minimum of two layers, and why deposit chemistry at the surface — not just thickness — must be verified. The mill is relaxed about surface iron contamination — but that statement is about incidental contamination, not about structural dilution from a steel substrate. Do not conflate the two. No published dilution limits were found — specify deposit chemistry, not a dilution percentage.
4. Grinding and cleaning discipline — the most common field failure. Before welding, remove “all greases, cutting oils, crayon marks, machining solutions, corrosion products, paints, scale, dye penetrant solutions and other foreign matter“; the physical reason: “since the melting temperatures of surface oxides are usually much higher than the base metal, they are more likely to stay solid during welding and become trapped in the weld pool“. Condition a 25 mm (1 in.) wide band on both face and root to bright metal with an 80 or 120 grit flapper wheel. INTERPASS CLEANING IS MANDATORY (stainless wire brush, preferably while the weld is still warm); use dedicated stainless or nickel-alloy brushes and grinding media only.
5. Joint geometry. Nickel alloys have a sluggish weld pool and significantly shallower penetration than carbon or stainless steel: a larger included angle, wider root gap and reduced root face are required. Carrying a stainless-steel weld prep straight over to C-276 produces lack of fusion at the root.
6. Copper is not a concern here. Ni and Cu are fully mutually soluble, so nickel-base alloys are not susceptible to liquid-metal embrittlement (that is a cobalt-base concern).
7. NDE constraint. The alloy is non-magnetic — magnetic particle inspection is not applicable.
Machining
A caveat that must be stated: the figures below are what the mill publishes for the corrosion-resistant HASTELLOY alloy family, not for C-276 specifically, and they are conservative HSS and uncoated-carbide values. Publish them as “family starting parameters”.
The governing rules. 1) Machine in the solution-annealed condition. 2) Rigid setup, sharp tools, positive rake. 3) Heavy, constant feed and continuous tool engagement — the alloy work-hardens rapidly, and dwelling or rubbing creates a hardened layer that destroys the next pass and the tool. This, not the base hardness, is the dominant machining difficulty. 4) Modern PVD-coated carbide and ceramic inserts achieve substantially higher speeds, but no authoritative mill figures were located — do not publish modern speeds without a tooling-vendor citation. 5) Descaling after hot work: molten-salt bath → water quench → hydrochloric acid immersion → nitric-hydrofluoric acid, with thorough rinsing between steps. Sulpho-chlorinated tapping compound must be completely removed before any heat treatment or welding — residual sulphur causes hot cracking.
Corrosion — Where It Is Outstanding and WHERE IT FAILS
In one sentence: C-276 is a reducing-acid alloy. Its 16 % chromium makes it good against chloride and moderate oxidising power, but it is insufficient in strongly oxidising media, and at high potential the molybdenum dissolves transpassively — the very element that makes the alloy good betrays it in its worst condition.
A) Where it is outstanding
Chlorine chemistry. C-276 “was developed initially for use with wet chlorine“; wet chlorine “requires Alloy C-276 or titanium“, and the alloy is the standard valve-stem material in carbon-steel dry-chlorine lines because the stem sees humid air. It is highly resistant to concentrated solutions of oxidising salts including iron and copper chloride. Hypochlorite: qualitatively excellent, BUT NO QUANTITATIVE RATE DATA WAS LOCATED at any stated concentration and temperature — DO NOT PUBLISH A NUMBER. For chlorine dioxide see the failure section below: the field data are worse than the marketing claim.
PREN — do not publish a single number. One publisher prints 45.2, another 65–75. The common nickel-alloy formula PREN_W = Cr + 3.3 × (Mo + 0.5 × W) applied to nominal C-276 (16 Cr, 16 Mo, 4 W) gives ≈75; 45.2 is not reproducible from any standard formula and looks like a transposition of 75.2. The correct practice: state the formula and the composition used, give ≈68–76 depending on whether tungsten is counted, and warn explicitly that PREN is a RANKING INDEX developed for stainless steels and is NOT a validated predictor for Ni-Cr-Mo alloys.
B) Where it fails or is over-specified — read this before quoting
This is the commercially valuable section. In Turkish and European projects C-276 is over-specified far more often than it is under-specified — and in the few places it is not, it genuinely fails.
1. Hot concentrated hydrochloric acid — the hard limit. From the mill’s own data: at 79 °C both 10 % and 20 % HCl attack at ≈1.1–1.2 mm/y — roughly 11–12 mm of wall over ten years, unacceptable for almost any pressure vessel. 20 % HCl at 100 °C: 154 mpy = 3.9 mm/y; 1 % HCl at boiling: 0.34 mm/y. The defensible limit: good resistance (<0.5 mm/y) in all concentrations ONLY up to about 50 °C; above roughly 65–80 °C in concentrated HCl you are outside the envelope. The right answer there is a higher-molybdenum nickel alloy (the mill points to its 22 % Mo grade as having “much broader ‘very safe’ and ‘moderately safe’ regimes“), tantalum, or a non-metallic lining.
2. Nitric acid and strong oxidisers — a genuine EXCLUSION. The mill’s own rates (mm/y): 10 % HNO₃ — 66 °C: 0.03, 93 °C: 0.26; 30 % — 66 °C: 0.14, 79 °C: 0.17; 60 % — 66 °C: 0.42, 79 °C: 0.82. 60 % HNO₃ at only 79 °C already gives 0.82 mm/y — an order of magnitude above the 0.1 mm/y “safe” line, and this is dilute-to-medium nitric at a modest temperature. Two publishers state the alloy “lacks sufficient chromium content to operate successfully in the most strongly oxidizing environments like hot, concentrated nitric acid“; the mill rates nitric resistance at 16 % Cr as only “moderate” and says C-2000 with 23 % Cr is better. Do not specify C-276 for nitric acid, nitric/HF pickling or mixed-acid oxidising service. The correct alloys are 304L/316L class, alloy 20, or a 23 % Cr nickel alloy (C-2000, 59).
3. Transpassive attack — chlorine dioxide bleach plants. This is the best-documented real failure mode and it directly contradicts the common “resists chlorine dioxide solutions” claim. Potentiostatic testing at +900 mV_SCE, 70 °C, 600 ppm Cl⁻: pH 6.5 — unwelded 0.47, GTAW-welded 0.47 mm/y; pH 2 — 0.39 and 0.38 mm/y. Welding made no difference. At pH 6.5 N10276 was attacked by uniform (transpassive) corrosion, while the super-austenitic S32654 in the same test corroded at 0.004 mm/y — more than 100× lower. The alloy goes transpassive at 600–700 mV_SCE, independent of pH between 2 and 6.5. Field coupons in neutral D-stage gave up to 0.1 mm/y, and the report notes it “performed well in straight chlorine bleach but showed high corrosion rates when chlorine dioxide substitution increased“. The mechanism to state: MOLYBDENUM, the element that makes C-276 good in reducing acid, is DISSOLVED TRANSPASSIVELY at high potential. Raising the redox potential — ClO₂, high free chlorine, strong oxidising biocides — moves the alloy from its best regime to one of its worst.
4. It is NOT immune to crevice corrosion. CCT 55 °C in acidified 6 % FeCl₃, independently corroborated at 60 °C → CCT ≈55–60 °C. More striking still: in quiescent seawater at only 29 °C, 1–2 crevice sites initiated to 0.10–0.13 mm depth over 180 days — the alloy’s OWN manufacturer documents crevice initiation at ambient seawater temperature. C-2000 reaches CCT 80 °C in the same test. Never write “immune to crevice corrosion.” Write instead: “outstanding but not unlimited crevice resistance; crevice threshold in ferric chloride ≈55–60 °C; design out crevices regardless of alloy — gaskets, tube-to-tubesheet joints, lap joints, deposits”.
5. Over-specification patterns to challenge. C-276 for chloride SCC only: if the only driver is chloride SCC and the medium is mildly corrosive, a duplex (F53, F55) or a 6 % Mo super-austenitic may be a fraction of the cost; C-276 earns its premium when reducing acid and chloride occur TOGETHER. C-276 for high-temperature structural service: ASME allows 677 °C but the metallurgy limits practical corrosion service to roughly 427 °C; the right families are 625, Hastelloy X, 800H and 230. C-276 in ambient seawater with crevices: Titanium Gr 2 is “very resistant to crevice attack in sea water at normal temperatures” and is often cheaper — choose C-276 when reducing acid, HCl or chlorine chemistry is present; choose titanium when the duty is essentially oxidising seawater or hypochlorite. C-276 where C-22/59/686 is technically required: oxidising or oxidising-chloride duties — specifying C-276 “because it is the best alloy” is wrong here.
Frequently Asked Questions
Our carbon-steel vessel is corroding in a 15 % HCl process at 85 °C. Is C-276 the upgrade?
Almost certainly not, and this is the most expensive mistake buyers make with this alloy. C-276’s reputation in hydrochloric acid is real but it is a low-temperature reputation: two independent publishers give the same envelope — good resistance, below 0.5 mm/y, in all concentrations but only up to about 50 °C (120 °F). The mill’s own reagent-grade data show that at 79 °C both 10 % and 20 % HCl attack C-276 at roughly 1.1–1.2 mm/y — call it 11 mm of wall loss over a ten-year design life, before you add any corrosion allowance. At 100 °C in 20 % HCl the published figure is 154 mpy = 3.9 mm/y. At 85 °C you are sitting between those two data points, on a curve that is climbing steeply. Worse, the number is fragile: dissolved oxygen “may drastically accelerate the corrosion attack since it is not a strong enough oxidizer to passivate Alloy C-276“. Any aeration, any ferric or cupric carry-over from upstream steel, any oxidising biocide, and the real rate diverges from the reagent-grade chart.
Ask three questions before quoting. What is the actual maximum temperature, including upset and steam-out? Is the stream aerated or does it carry oxidising contaminants? What corrosion allowance and design life does the client want? If the answer is a sustained 85 °C, C-276 is outside its envelope. The honest recommendations are a higher-molybdenum nickel alloy, tantalum for the hot spots, or a PTFE/graphite-lined vessel. Selling C-276 into this duty produces a failure in eighteen months and loses the account; selling the correct alloy — or honestly declining — keeps it.
Our fabricator wants to stress-relieve the C-276 weldments at 620 °C like they do for our carbon-steel vessels. Is that acceptable?
No. Refuse it in writing. This is a genuine, recurring field failure caused by carbon-steel habits carried into nickel-alloy work. C-276 is solid-solution strengthened, not precipitation-hardened, and its whole design premise is that it can be used as welded. Its extremely low carbon (0.010 % max) and silicon (0.08 % max) exist so that the brief weld thermal cycle does not produce continuous grain-boundary precipitation — the mill states the alloy is formulated so that “short-term thermal excursions above 500 °C (as encountered during welding) do not cause continuous precipitation“.
A 620 °C soak is not a short excursion. It sits inside the precipitation window. The mill’s C-276 welding data page is explicit: “Post-weld stress relieving in the 1200 °F (650 °C) range is not recommended.” Its welding brochure explains why: intermediate-temperature stress relief at 540–815 °C causes “precipitation of secondary phases in the microstructure which can have a detrimental effect on material properties, such as corrosion resistance“. Another producer puts it bluntly: “Stress relief heat treatments are not effective” — a full anneal should be used instead. The controlling reaction is M₆C carbide, which forms between 650 and 1038 °C and does so even at 0.005 % carbon; molybdenum partitions into it, leaving a depleted, corrosion-prone boundary.
The only acceptable post-weld heat treatment is a full solution anneal at roughly 1100–1160 °C followed by a rapid water quench — and for most vessels that is impractical, which is precisely why the alloy was designed to need no PWHT at all.
The mill certificate says ASTM B575 and all elements are in range. Is the material fit for our European sour-service project?
Conformance to ASTM B575 alone does not answer that question, and THREE separate gaps can bite you.
First, the ASTM/EN chemistry divergence. ASTM B575 permits P ≤0.04 % and S ≤0.03 %. The German route under VdTÜV 400 permits only P ≤0.025 %, S ≤0.010 %, and one mill’s own material is tighter still at 0.02 % / 0.01 %. A heat at S = 0.025 % is perfectly ASTM-conforming and three times the DIN sulphur ceiling — and sulphur and phosphorus are the impurity elements the mill names as driving weld solidification cracking. If the project is CE-marked under PED using VdTÜV 400, ASTM-only material may not be acceptable at all.
Second, mechanical minima are not equivalent. ASTM demands 283 MPa / 690 MPa / 40 %; VdTÜV 400 for sheet ≤5 mm demands 310 MPa / 730 MPa but only 30 %. Neither set dominates the other.
Third, NACE status is not automatic. C-276 is listed in NACE MR0175 / ISO 15156 as a type 4e alloy, but compliance depends on delivery condition and hardness, and the certificate must state them. We could not verify the applicable hardness cap or the chloride/pH/elemental-sulphur limits against the standard itself and therefore publish no figures — confirm against the current edition of ISO 15156-3 Annex A. Note also that the ASTM F468 20–32 HRC band is a PRODUCT-SPECIFICATION limit, not the NACE cap.
Purchase-order language that closes all three gaps: “ASTM B575/SB-575 AND DIN 17744 / VdTÜV-Werkstoffblatt 400; P ≤0.020 %, S ≤0.010 %; solution annealed and water quenched; NACE MR0175/ISO 15156-3 compliant with condition and hardness stated on the certificate; ASTM G28 Method A result reported.“
The certificate shows an ASTM G28 result of 6.10 mm/y. Should we reject the material?
No — and the panic itself is a routine occurrence. ASTM G28 is not a service corrosion rate; it is a deliberately brutal, comparative screening test whose only purpose is to prove the material has not been sensitised — that there is no M₆C or intermetallic at the grain boundaries. It bears no relation to plant life. Look at the magnitudes: published G28 Method A rates are 6.10 mm/y (one producer’s material) and 4.05 mm/y (another’s), while quoted acceptance limits are 480 mpy (12.2 mm/y) for G28A and 300 mpy for G28B. So 6.10 mm/y is half the acceptance limit. The correct use of the result is pass/fail against the specified acceptance limit.
But the figure does say something genuinely important: rates vary measurably between producers of identically-specified material (6.10 vs 4.05) — which is itself a reason to require the test on every heat. HASTELLOY® is a trademark; generic C-276 (same UNS N10276, same ASTM) is fully legitimate, but ask for the certified corrosion test data from the actual supplying mill, not a generic datasheet.
Common Datasheet Errors and Traps — Check These Before You Order
Every item below was observed in a real published source.
1. Carbon limit quoted as 0.02 % instead of 0.010 %. Observed on one producer’s own datasheet and on a major distributor page. ASTM B575, B574, B619 and B622 all specify C ≤0.010 % max. Correction: 0.010 % max; reject certificates above it. 0.02 % C is precisely the condition C-276 was invented to eliminate.
2. Weld filler W.Nr. given as 2.4819. 2.4819 is the BASE METAL; the bare wire is 2.4886 and the covered electrode 2.4887. Ordering by that number can bring you base-metal bar instead of drawn wire.
3. Confusing the ERNiCrMo-4 and ENiCrMo-4 UNS numbers. ERNiCrMo-4 (bare wire, A5.14) = N10276; ENiCrMo-4 (covered electrode, A5.11) = W80276. Sites printing “ENiCrMo-4, UNS N10276” are wrong.
4. Mixing the AWS “E” and “ER” prefixes with the wrong spec number. Observed on a mill datasheet: “AWS A5.14 ENiCrMo-13″. A5.14 covers bare rod and wire (ER…); A5.11 covers covered electrodes (E…).
5. Quoting ASTM specification minima as “typical properties”. One distributor spec sheet prints 100 ksi / 41 ksi / 40 % / 100 HRB under the heading “Typical”; those are the ASTM B575 MINIMA. Real annealed C-276 typically tests at 741–796 MPa UTS and 347–376 MPa yield — roughly 25–30 % above the minimum. Always label which you are quoting; otherwise a buyer told the “typical” is 100 ksi UTS may reject perfectly good material testing at 102 ksi as “barely passing”.
6. Reading the ASME Section VIII maximum temperature as a service recommendation. VIII Div. 1 permits 677 °C; the mill’s own metallurgy guide states the microstructure is metastable only to about 427 °C, and M₆C forms from 650 °C upward. A vessel operated continuously at 600 °C is code-legal and metallurgically doomed. Code ceiling 677 °C; practical corrosion-service ceiling ≈425 °C.
7. Averaging or cherry-picking CPT and CCT. Published CPT spans 60 °C to >150 °C and CCT 55 to 105 °C, depending entirely on test medium and method. A page printing a bare “CPT 150 °C” without naming the medium is not wrong so much as meaningless — and it will be quoted back at you after a crevice failure at 65 °C. Always print medium + method + duration.
8. “Immune to crevice corrosion.” Contradicted by the manufacturer’s own data: CCT 55 °C and 1–2 crevice sites initiating to 0.10–0.13 mm in quiescent seawater at just 29 °C over 180 days. C-2000 reaches CCT 80 °C. Correction: outstanding, not immune.
9. PREN = 45.2. Not reproducible from any standard formula; Cr + 3.3(Mo + 0.5 W) gives ≈75 and another publisher quotes 65–75 — the figure looks like a transposition of 75.2. More fundamentally, PREN is a ranking index for stainless steels and is not a validated predictor for Ni-Cr-Mo alloys. Publish the formula, the range and the caveat — never a bare number.
10. Claiming excellent nitric acid resistance. The mill’s own data give 60 % HNO₃ at 79 °C = 0.82 mm/y, and two publishers state the alloy “lacks sufficient chromium content to operate successfully in the most strongly oxidizing environments“. Correction: C-276 is a reducing-acid alloy. For nitric, use a high-Cr grade.
11. Claiming clean chlorine-dioxide resistance. Potentiostatic data show N10276 corroding at 0.39–0.47 mm/y at +900 mV_SCE, 70 °C, 600 ppm Cl⁻ by uniform transpassive attack — while S32654 in the same test gave 0.004 mm/y; welding made no difference. Correction: good in straight chlorine bleach; it degrades as chlorine dioxide substitution rises, because Mo dissolves transpassively at high potential.
12. Treating C-22 as “better C-276” (or vice versa). They are a Cr/Mo trade-off, not a ladder: C-276 is better in reducing environments, C-22 in oxidising ones. Additionally, the mill states C-22 is “very prone” to Ni₂(Cr,Mo) ordering in the 300–650 °C range while C-276 is less susceptible.
13. Unit errors in the melting range. One distributor prints “2415–2500 °C“; those are °F. The correct value is 1323–1371 °C.
14. Cold-work re-anneal threshold quoted as a single number. The mill: 7 % (for SCC resistance); three European sources: 15 % (for ductility). For sour or chloride-SCC service, use the 7 % trigger; quoting only 15 % will cost somebody a cracked bend.
15. Interpass temperature quoted as 120 °C. One mill gives 120 °C; the originating mill gives 93 °C (200 °F) in two separate documents. Default to 93 °C.
16. Assuming “solution annealed” on a certificate means correctly quenched. The most precise published criterion: air cooling is acceptable only below 1.5 mm and only if 1000 → 600 °C is traversed within 2 minutes. A slow-cooled part carries grain-boundary M₆C and has the intergranular corrosion behaviour of alloy C. The certificate should state the quench medium, not just “annealed”.
17. Assuming wire is covered by an ASTM specification. There is no ASTM or ASME product specification for N10276 wire; only DIN 17753 / ISO 9723-9725 apply and wire mechanicals are by agreement. Never write “ASTM B574 wire”.
18. Attributing the alloy’s invention to the wrong company. One educational source states C-276 was “developed by German company BASF using the novel AOD process“. C-276 is a Haynes International (formerly Haynes Stellite / Cabot) alloy and HASTELLOY is a Haynes trademark. Do not repeat the attribution.
19. Sizing presses and heat exchangers from stainless-steel data. C-276 “is stiffer than most austenitic stainless steels” and “work hardens more readily“; its thermal conductivity is 9.2–10.5 W/m·K, roughly a third of carbon steel. Carrying over a 316L press tonnage or a carbon-steel exchanger area is a recurring design error.
Related grades
Hastelloy C-2000 · Hastelloy X · Monel 400 · Monel K-500 · All nickel alloys →