Hastelloy C-276
Also: Hastelloy C-276, Alloy C-276, C276, UNS N10276, Inconel C-276, Nickel alloy C-276, W.Nr. 2.4819, NiMo16Cr15W, Nicrofer 5716 hMoW, ERNiCrMo-4 (filler)
Hastelloy C-276 handles the worst wet chemistry: wet chlorine, bleach, ferric chloride and hot acids. 690 MPa (100 ksi) tensile, welds as-is. Values annealed.
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At a glance
| Density | 8.89 g/cm³ (0.321 lb/in³) |
|---|---|
| Tensile strength | 690 MPa (100 ksi) min; typically 790 MPa (115 ksi) |
| Yield strength | 283 MPa (41 ksi) min; typically 355-415 MPa (52-60 ksi) |
| Hardness | About 90 HRB (185-210 HB) |
| Elongation | 40% min; typically 50-60% |
| Modulus of elasticity | 205 GPa (29.8 Msi) |
| Thermal | Melts at 1323-1371 °C (2415-2500 °F); thermal conductivity ~10 W/m·K; oxidation resistant to about 1040 °C (1900 °F), but corrosion service is normally below about 400 °C (750 °F) |
| Composition | Ni balance (about 57%), Mo 15-17%, Cr 14.5-16.5%, Fe 4-7%, W 3-4.5%, Co up to 2.5%, Mn up to 1%, C up to 0.01%, Si up to 0.08% |
Typical values, Solution annealed at about 1120 °C (2050 °F) and rapidly quenched, per ASTM B575 / B574 (the only condition it is sold in). Confirm against the mill certificate and the purchase spec.
- MachinabilityPoor
- About 15-20% of the free-machining steel benchmark; work-hardens severely and holds heat at the tool. Rigid setup, sharp positive-rake carbide, low speed, heavy steady feed and flood coolant; never rub or dwell. Plan 8-12x the cycle time of 6061.
- WeldabilityExcellent
- TIG, MIG and plasma with ERNiCrMo-4 filler, as welded, no post-weld heat treatment. The low carbon and silicon keep the heat-affected zone corrosion resistant, which is what distinguishes it from older alloy C. Low heat input and clean joints.
- FormabilityGood
- Forms cold in the solution-annealed condition with about 2x the force of 304 stainless and heavy springback; deep draws and spins with intermediate anneals. Hot work at 950-1230 °C (1750-2250 °F), followed by a solution anneal and quench.
- Corrosion resistanceExcellent
- Resists wet chlorine, hypochlorite, chlorine dioxide, ferric and cupric chlorides, hot contaminated mineral and organic acids, seawater and sour gas; immune to chloride stress-corrosion cracking and highly resistant to pitting and crevice attack. Limited in hot, strongly oxidizing acids such as boiling nitric, where alloy C-22 or a titanium grade does better.
Hastelloy C-276 is a nickel-molybdenum-chromium alloy with tungsten, and very low carbon and silicon. The molybdenum and tungsten defend it in reducing environments and against pitting and crevice attack; the chromium covers oxidizing conditions. The result is the most versatile corrosion-resistant alloy in common use: wet chlorine gas, hypochlorite and chlorine dioxide bleach, ferric and cupric chlorides, hot contaminated sulfuric, phosphoric, acetic and formic acids, and sour gas. Its low carbon means it stays corrosion resistant in the heat-affected zone of a weld without post-weld annealing, which was the whole point of developing it from the older alloy C.
It is used where 316 stainless, duplex and even Inconel 625 pit, crack or dissolve: chemical reactors and columns, flue gas desulfurization scrubbers and stack liners, pulp and paper bleach plants, pharmaceutical process equipment, waste incinerators, pickling and plating tanks, and sour gas wellhead components. Its strength, about 690 MPa (100 ksi) minimum tensile annealed with 40% elongation, is adequate for pressure equipment and is often secondary to its chemistry.
It fabricates like a nickel alloy: welds well with matching ERNiCrMo-4 filler, forms with high forces and springback, and machines slowly with severe work hardening. It is one of the most expensive common alloys, so it is often applied as a weld overlay, a clad plate or a thin liner rather than as solid section. For strongly oxidizing media, such as hot nitric acid, the sister alloy C-22 (UNS N06022) is the better choice.
Heat treatment
Not hardenable; the alloy is supplied solution annealed at about 1120 °C (2050 °F) with a water quench or rapid air cool, and that is the only heat treatment it should see. Re-solution anneal after hot working or heavy cold forming to restore corrosion resistance and ductility. Avoid slow cooling or holding between about 650 and 1090 °C (1200-2000 °F), which precipitates molybdenum-rich phases at grain boundaries and reduces corrosion resistance; welding is fine because the exposure is brief.
Tempers and conditions
- Solution annealed (the only supplied condition)
- Cold worked (strip and wire, limited)
Stock forms
- Plate
- Sheet and strip
- Round bar
- Seamless and welded pipe and tube
- Forgings, flanges and fittings
- Welding wire and overlay
- Clad plate
Relative cost
Tier 5 of 5. Roughly 12-20x the price of 304 stainless per pound, above Inconel 625, because of the molybdenum and tungsten; machining runs 8-12x aluminum time. Weld overlay, clad plate and thin liners are how most equipment gets C-276 chemistry at a bearable cost.
Typical applications
- Chemical process reactors, columns, heat exchangers and piping
- Flue gas desulfurization scrubbers, stack liners and dampers
- Pulp and paper bleach plant equipment
- Pharmaceutical and fine chemical reactors and agitators
- Waste incinerator and hazardous waste treatment components
- Pickling, plating and acid recovery equipment
- Sour gas wellhead, valve and downhole components
- Pumps, valves and seals for aggressive chemical service
Process compatibility
How C-276 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | PoorPoor | Slow, work-hardening and abrasive; carbide at low speed, heavy feed and flood coolant. Keep machined detail to a minimum and put geometry into cut, formed and welded parts. |
| Welding | ExcellentExcellent | ERNiCrMo-4 filler by TIG, MIG or plasma, as welded, with the heat-affected zone retaining full corrosion resistance; the reason the alloy exists. |
| TIG Welding | ExcellentExcellent | Low heat input, stringer beads, argon shielding, clean joints; interpass temperature below about 95 °C (200 °F). |
| Sheet Metal Fabrication | GoodGood | Sheet and plate cut, form and weld into scrubber liners, ducting, tanks and reactor internals; allow for high forming forces and springback. |
| Press Brake Forming | GoodGood | Bend solution-annealed sheet at about 1-2x thickness inside radius with 5-10 degrees of overbend; forces about 2x those for 304 stainless. |
| Deep Drawing | FairFair | Draws with polished, lubricated tooling and intermediate solution anneals; work hardening limits the draw ratio per pass. |
| Laser Cutting | GoodGood | Fiber lasers cut sheet and plate to about 12 mm (1/2") with nitrogen assist; the edge is clean and only slightly hardened. |
| Waterjet Cutting | ExcellentExcellent | Any plate thickness with no heat-affected zone; the standard route for thick C-276 plate and flange blanks. |
| Plasma Cutting | FairFair | Rough profiling of thick plate; the heat-affected edge should be machined back before welding on corrosion-critical parts. |
| Forging | FairFair | Forged flanges, fittings and valve bodies at 950-1230 °C (1750-2250 °F) with a narrow working window and high flow stress; then solution anneal and quench. |
| Investment Casting | FairFair | Cast as CW-12MW / CW-2M (ASTM A494) for pump casings and valve bodies; cast versions are slightly less corrosion resistant than wrought. |
| Metal 3D Printing | GoodGood | Prints well by laser powder bed for impellers, heat exchangers and chemical process parts; solution anneal and HIP afterward. |
| Electropolishing | GoodGood | Electropolishes to a clean, passive surface for pharmaceutical and high-purity service. |
| Heat Treating | Not recommendedNot recommended | Cannot be hardened, and any hold between 650 and 1090 °C (1200-2000 °F) precipitates grain-boundary phases that cut corrosion resistance. Solution anneal and quench is the only treatment. |
Design and sourcing tips
- Specify "Hastelloy C-276 per ASTM B575 (plate, sheet) or B574 (bar), solution annealed"; add NACE MR0175 when the service is sour.
- Use it where the chemistry demands it: wet chlorine, hypochlorite, ferric chloride, hot mixed or contaminated acids. For plain seawater or mild acids, 625, duplex or 316 costs far less.
- Design welded, as-welded, with ERNiCrMo-4 filler; no post-weld heat treatment, but call out low heat input and clean, degreased joints.
- Consider clad plate or weld overlay on carbon steel for vessels and large flat parts; solid C-276 is for thin sections, complex shapes and small parts.
- For hot, strongly oxidizing acids (nitric, hot chromic) compare alloy C-22, and for hydrofluoric acid compare Monel 400.
- Keep machining to a minimum: put the geometry into laser-cut, formed and welded sheet, and reserve milling for sealing faces and threads.
Frequently asked questions
- What is Hastelloy C-276 used for?
- The most aggressive wet chemical service: flue gas scrubbers, chlorine and bleach plant equipment, pharmaceutical and fine chemical reactors, waste incinerators, pickling and plating tanks, and sour gas wellheads. It is chosen when stainless, duplex and Inconel 625 pit, crack or corrode in the same environment.
- What is the difference between Hastelloy C-276 and C-22?
- C-22 has more chromium (about 22%) and less molybdenum and tungsten, so it does better in oxidizing acids such as nitric and in mixed oxidizing-reducing conditions, and it resists grain-boundary precipitation during welding a little better. C-276 is stronger in reducing acids and hot wet chlorine. They cost about the same and are often interchangeable; C-276 is the more widely stocked.
- Can Hastelloy C-276 be welded?
- Yes, and it is welded as is: TIG, MIG or plasma with ERNiCrMo-4 filler, no preheat and no post-weld heat treatment. Because carbon and silicon are held very low, the heat-affected zone keeps its corrosion resistance, which is what separates C-276 from the older alloy C. Use low heat input, stringer beads and clean joints.
- Is Hastelloy C-276 magnetic?
- No. It is a fully austenitic nickel alloy and is non-magnetic in the solution-annealed and welded conditions. A magnet will not tell it apart from Inconel 625 or austenitic stainless.
- How much does Hastelloy C-276 cost compared to stainless?
- Roughly 12-20x the price of 304 stainless per pound, and it takes far longer to machine. That is why most C-276 equipment uses thin sheet, clad plate or weld overlay rather than solid section, and why it is specified only where the chemistry demands it.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM B575 and ASTM B574 (property minimums by form)
- Haynes International Hastelloy C-276 alloy data sheet
- NACE MR0175 / ISO 15156 (sour service limits)
- ASM Handbook, Volume 13B (Corrosion: Materials)
