Chemical processing
Reactor vessels, heat exchangers, valves handling sulfuric, hydrochloric, chlorine, hypochlorite, and mixed-acid streams.
Ni-Cr-Mo-W superalloy · UNS N10276
Hastelloy C-276
The corrosion-resistance king. Nickel-molybdenum-chromium-tungsten superalloy that survives reducing acids, oxidizing acids, chlorides, and brines that destroy stainless. Standard for chemical processing, pollution control scrubbers, and sour gas wells.
UTS
790 MPa
Density
8.89 g/cc
Modulus
205 GPa
Mach.
18 /100
When to use
Pick C-276 when stainless has failed by corrosion.
Hastelloy C-276 (Haynes International’s alloy, also produced as Inconel C-276 by Special Metals) is the standard for the most aggressive corrosion service. Where 316L would pit, where titanium would crack from chloride stress corrosion, where Inconel 625 would still corrode in the wettest reducing environments — C-276 holds. The nickel base provides the corrosion resistance, the 16% molybdenum gives it pitting resistance, and the tungsten + chromium handle oxidizing conditions.
The catch is severe machinability (18/100, nearly as bad as Inconel 718) and material cost — the most expensive part of the job. Stock cost runs $50-80/lb, and machining cycle times are 4-6× steel. Use it when the corrosion service genuinely requires it; cheaper alloys serve most other applications.
Strengths
Why chemical industry runs it.
- Universal corrosion resistanceOne of the few alloys resistant to BOTH oxidizing and reducing media — sulfuric, hydrochloric, chlorine, hypochlorite, hot caustic.
- Pitting & crevice resistancePREN ~70. Standard against chloride stress corrosion in seawater, brine, and salt environments.
- Sour gas qualifiedNACE MR0175 / ISO 15156 qualified for H₂S service. Used in sour-gas wellhead and downhole hardware.
- High-temp capableMaintains corrosion resistance and reasonable strength up to 1038 °C (1900 °F).
- WeldableWeldable with matching filler (ERNiCrMo-4) without post-weld heat treatment for most thicknesses.
- Cryogenic capableMaintains ductility down to liquid hydrogen temperatures — used in cryogenic chemical handling.
Trade-offs
What you accept for the corrosion.
- Cost$50-80/lb stock — among the most expensive commonly-machined alloys. Material is often >70% of finished part cost.
- Machinability 18/100Nearly as difficult as Inconel 718. Tooling and cycle time both major cost drivers.
- Density penalty8.89 g/cc — same as steel. No weight savings vs cheaper alloys.
- Lower strength than precipitation-hardening alloysUTS 790 MPa is half of Inconel 718 H-aged. Pick C-276 for corrosion, not strength.
- Long lead timesSpecialty alloy from a few mills — bar stock lead times of 6-12 weeks aren't unusual.
- Work hardens aggressivelySingle rubbing pass and the surface is harder than your tool. Same machining philosophy as Inconel 718.
Specs
Mechanical, physical & chemical data.
Properties for solution-annealed C-276 bar per ASTM B574. Cold work increases strength substantially but is rarely used because annealed condition has the best corrosion behavior.
Mechanical
Properties (annealed)
| Ultimate tensile strength | 790 MPa (115 ksi) |
|---|---|
| Yield strength (0.2% offset) | 360 MPa (52 ksi) |
| Elongation at break | 60% |
| Reduction of area | 70% |
| Modulus of elasticity | 205 GPa |
| Hardness (annealed) | ≤ 90 HRB |
| Cold-worked UTS (max) | 1240 MPa |
| Charpy V-notch at 21 °C | 200 J |
Source: Haynes International datasheet. UTS at 540 °C: 580 MPa; 815 °C: 270 MPa. Maintains useful strength to ~870 °C.
Physical & thermal
At room temperature
| Density | 8.89 g/cc (0.321 lb/in³) |
|---|---|
| Melting range | 1325 – 1370 °C |
| Specific heat | 0.428 J/g·°C |
| Thermal conductivity | 9.8 W/m·K |
| CTE (20–100 °C) | 11.2 µm/m·°C |
| Electrical resistivity | 1.30 µΩ·m |
| Magnetic | Non-magnetic |
Lower thermal conductivity than even Inconel — heat retention drives the machining challenge.
Composition
Chemistry, weight %
| Nickel (Ni) | balance (~57%) |
|---|---|
| Chromium (Cr) | 14.5 – 16.5 |
| Molybdenum (Mo) | 15.0 – 17.0 |
| Iron (Fe) | 4.0 – 7.0 |
| Tungsten (W) | 3.0 – 4.5 |
| Cobalt (Co) | 2.5 max |
| Carbon (C) Strict — for corrosion behavior | 0.01 max |
| Manganese (Mn) | 1.0 max |
| Vanadium (V) | 0.35 max |
| Silicon (Si) | 0.08 max |
The ultra-low carbon (0.01% max) prevents carbide precipitation that would otherwise sensitize the alloy and reduce corrosion resistance.
Specifications
Common purchase specs.
AMS 5750
Bar — solution annealed
ASTM B574
Rod and bar — Ni-base alloy
ASTM B575
Sheet, strip, plate
ASTM B622
Seamless pipe and tube
NACE MR0175
Sour gas service qualification
ISO 15156
Petroleum & gas — H₂S environments
Machining
How we cut it.
Same playbook as Inconel 718 — slow speeds, heavy feeds, sharp tools, rigid setups, and high-pressure coolant. C-276 work-hardens fast, so any rubbing creates a hardness layer that wrecks the next tool.
Cutting speed
30–50 SFM with carbide turning. 50–80 SFM milling. Sharp tools mandatory.
Feed rate
Heavy. Light feed = rubbing = work hardening = catastrophic tool failure.
Depth of cut
Aim deeper than any work-hardened layer from the previous pass — typically 0.030″+ for roughing.
Tooling
Coated carbide (TiAlN/AlTiN) for general work. Whisker-reinforced ceramic for high-speed turning.
Coolant
High-pressure (1000+ psi) through-tool flood. Heat removal is everything.
Climb mill always
Conventional milling rubs and work-hardens. Climb is mandatory.
Rigid setup
Vibration accelerates wear exponentially. Short overhangs, heavy fixturing.
No dwell ever
Stop the feed = work harden the surface = tool failure on next pass.
Applications
Where C-276 earns its cost.
Pollution control
FGD scrubbers, acid absorbers, stack components in coal/incineration plants. Survives wet hot SO₂/SO₃ environments.
Oil & gas — sour service
Wellhead components, downhole tools, valves in sour gas wells. NACE MR0175 / ISO 15156 qualified for H₂S exposure.
Compare
Related materials.
Higher strength
Inconel 718 →
Higher strength, less corrosion. Pick when load matters more than chemistry.
Lower-cost stainless
316L Stainless →
When the chemistry is moderate — saves 80% of the material cost.
Lighter alternative
Ti-6Al-4V →
For seawater + chloride. Half the weight; weaker in reducing acids.
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