Alloy C276,Hastelloy C276 ,UNS N1276

Alloy C276,Hastelloy C276 ,UNS N1276

Alloy C276 (Hastelloy C276, UNS N1276) - Introduction with Composition, Properties, Applications and Product Forms

Alloy C276, commercially known as Hastelloy C276 and designated by UNS N1276, is a premium nickel-molybdenum-chromium superalloy celebrated as one of the most corrosion-resistant materials globally. Engineered to withstand the harshest chemical and thermal environments—including aggressive acids, chloride-rich solutions, and elevated temperatures—it is a cornerstone material in industries where component failure due to corrosion is costly or hazardous. It is available in a comprehensive range of forms to meet diverse industrial needs, including Bar (Round bar, Flat bar), Ribbon, Wire, Rods, Tube, Pipe, Foil, Plate, Sheet, Strip, and Forging Stock. Hastelloy C276 Wire, in particular, stands out for its uniform corrosion resistance and flexibility, making it ideal for welding, thermal spray coatings, and precision components in chemical processing and offshore applications. Below is a detailed overview of its chemical composition, key properties, practical applications, and available product forms.

Chemical Composition

The precisely balanced chemical composition of Alloy C276 (Hastelloy C276, UNS N1276) is the foundation of its exceptional corrosion resistance and mechanical performance. The typical composition (by weight) is as follows:

Nickel (Ni): 57-63% (the primary matrix element, providing a stable base for corrosion resistance and serving as a host for strength-enhancing alloying elements; it also resists chloride-induced stress corrosion cracking)

Molybdenum (Mo): 15-17% (the key contributor to resistance against pitting, crevice corrosion, and reducing environments—e.g., hydrochloric acid—by forming a protective layer that inhibits localized corrosion)

Chromium (Cr): 14.5-16.5% (forms a dense, adherent chromium oxide layer, ensuring superior resistance to oxidation, sulfidation, and oxidizing acids like nitric acid)

Iron (Fe): 4-7% (improves fabricability and balances the alloy’s microstructure without compromising corrosion resistance; also enhances thermal conductivity)

Tungsten (W): 3-4.5% (works with molybdenum to boost pitting and crevice corrosion resistance, especially in chloride-rich media, and enhances high-temperature strength)

Cobalt (Co): ≤ 2.5% (strictly limited to avoid reducing corrosion resistance in aggressive environments, as excess cobalt can promote localized attack)

Carbon (C): ≤ 0.01% (minimized to prevent carbide precipitation at grain boundaries—carbides could deplete chromium near boundaries, creating corrosion-susceptible zones)

Silicon (Si): ≤ 0.08% (controlled to avoid forming brittle silicides and to preserve corrosion resistance in acid environments)

Manganese (Mn): ≤ 1% (aids in deoxidation during manufacturing and improves hot workability, enabling fabrication into thin forms like foil and strip)

Phosphorus (P): ≤ 0.04% (limited to prevent grain boundary embrittlement and reduce the risk of stress corrosion cracking)

Sulfur (S): ≤ 0.03% (minimized to ensure good ductility and resistance to stress corrosion cracking in harsh chemical environments)

This engineered blend—focused on nickel, molybdenum, and chromium—delivers Alloy C276’s signature "all-environment" corrosion resistance, making it suitable for both oxidizing and reducing media.

Key Properties

Alloy C276 (Hastelloy C276, UNS N1276) and its various forms exhibit exceptional properties that make them indispensable in corrosive, high-temperature, and cyclic-stress environments:

Corrosion Resistance (Core Advantage)

General Corrosion: Unmatched resistance to a broad range of corrosive media, including:

Strong reducing acids: Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (even at high concentrations and temperatures).

Oxidizing acids: Nitric acid (HNO₃), chromic acid, and mixed acids (e.g., HCl + HNO₃).

Alkaline solutions: Caustic soda (NaOH) and ammonia, even at elevated temperatures.

Chloride-rich media: Seawater, brines, and chloride-containing process streams (resists pitting and crevice corrosion up to ~100°C/212°F).

Pitting & Crevice Corrosion: Exceptional resistance—maintains integrity in 6% ferric chloride solution (a severe test for pitting) with no attack at temperatures up to 40°C/104°F, outperforming most other nickel alloys.

Stress Corrosion Cracking (SCC): Highly resistant to SCC in chloride, hydrogen sulfide (H₂S), and sour gas environments—critical for offshore oil and gas and chemical processing applications.

Erosion-Corrosion: Combines corrosion resistance with good ductility, enabling it to withstand fluid flow-induced wear in aggressive process streams (e.g., slurry transport in mining).

Mechanical Properties (Annealed Condition)

Tensile Strength: 690-896 MPa (100,000-130,000 psi) at room temperature; retains ~450 MPa (65,300 psi) at 500°C (932°F)

Yield Strength (0.2% offset): 310-414 MPa (45,000-60,000 psi) at room temperature; retains ~275 MPa (39,900 psi) at 500°C (932°F)

Elongation (in 50 mm): 40-60% (excellent ductility, enabling cold forming into complex shapes like tube bends and sheet metal components)

Reduction of Area: 50-70% (superior toughness, resisting fracture under mechanical stress and thermal cycling)

Hardness: 180-220 HB (Brinell hardness) at room temperature; maintains ~150 HB at 500°C (932°F)

Physical Properties

Density: 8.89 g/cm³ (0.321 lb/in³)

Thermal Conductivity: 11.1 W/(m·K) at 20°C (68°F); increases to 18.4 W/(m·K) at 500°C (932°F) (efficient heat transfer for heat exchanger applications)

Coefficient of Thermal Expansion: 12.3 μm/(m·K) (20-100°C/68-212°F); 14.8 μm/(m·K) (20-500°C/68-932°F) (controlled expansion to minimize thermal stress in assembled systems)

Modulus of Elasticity: 205 GPa (29,700 ksi) at room temperature; decreases to ~180 GPa (26,100 ksi) at 500°C (932°F)

Melting Point: 1325-1370°C (2417-2498°F)

High-Temperature Properties

Continuous Service Temperature: Up to 650°C (1202°F) (maintains corrosion resistance and mechanical strength; for short-term exposure, can withstand up to 870°C/1600°F)

Oxidation Resistance: Forms a stable chromium oxide layer, resisting scaling in air at temperatures up to 815°C (1500°F) for extended periods

Creep Resistance: Good creep performance at moderate temperatures—1000-hour creep rupture strength of ~100 MPa (14,500 psi) at 600°C (1112°F)

Product Forms

Alloy C276 (Hastelloy C276, UNS N1276) is manufactured in a diverse range of forms to accommodate specialized corrosive and high-temperature applications:

Bar: Round bar (diameters 6-200 mm) and Flat bar (thickness 5-100 mm, width 20-500 mm) — ideal for machining into valves, pumps, and fasteners for chemical processing and offshore equipment.

Ribbon: Thin, flat strips (thickness 0.07-0.8 mm, width 3-80 mm) — used in thermal spray coatings for corrosion protection on steel substrates and in flexible seals for chemical reactors.

Wire: Hastelloy C276 Wire (diameters 0.3-6 mm) — serves as welding filler metal (TIG/MIG) for joining C276 components and as precision heating elements in corrosive environments.

Rods: Solid cylindrical rods (diameters 2-50 mm) — used for GTAW filler metal and manufacturing small components like sensor probes and valve stems.

Tube and Pipe: Seamless/welded tube (outer diameter 4-150 mm, wall thickness 0.5-10 mm) and pipe (NPS ½-12) — critical for transporting corrosive fluids (e.g., acid lines in chemical plants, offshore sour gas pipelines).

Foil: Ultra-thin sheets (thickness 0.012-0.1 mm) — used as corrosion-resistant liners for electronic components, pharmaceutical packaging, and thin-film gaskets.

Plate and Sheet: Plate (thickness 3-50 mm) and Sheet (thickness 0.2-3 mm) — fabricated into chemical storage tanks, heat exchanger plates, and reactor vessels.

Strip: Narrow, flat strips (thickness 0.07-2 mm, width 2-50 mm) — used for precision components like heat exchanger fins, electrical contacts, and seal rings.

Forging Stock: Billets and ingots (sizes up to 500×500 mm) — hot-forged into complex shapes (e.g., pump casings, turbine parts) requiring high corrosion resistance and strength.

Applications

The exceptional corrosion resistance and balanced mechanical properties of Alloy C276 (Hastelloy C276, UNS N1276) make it a staple in industries facing aggressive chemical or thermal conditions:

Chemical Processing

Acid Production & Handling: Components for hydrochloric, sulfuric, and nitric acid plants — including storage tanks (plate/sheet), transfer pipes (tube/pipe), and pump impellers (bar/forging stock).

Pharmaceutical & Food Processing: Corrosion-resistant equipment (e.g., mixers, reactors, and packaging foil) to avoid product contamination from metal leaching.

Petrochemicals: Catalyst regeneration systems, sour water strippers, and crude oil distillation units (resists H₂S and chloride corrosion).

Oil & Gas (Offshore & Onshore)

Offshore Platforms: Wellhead components, subsea pipelines (tube/pipe), and valve bodies (bar/forging stock) — withstands seawater, sour gas (H₂S), and brine corrosion.

Downhole Equipment: Tubing and casing for high-salinity, high-H₂S wells (resists SCC and pitting in downhole conditions).

Power Generation

Waste-to-Energy Plants: Combustion chamber liners (plate/sheet) and flue gas desulfurization (FGD) systems — resists corrosive flue gases and sulfuric acid byproducts.

Nuclear Power: Heat exchanger tubes (tube) and structural components in secondary coolant systems — resists radiation-induced corrosion and high-temperature water.

Environmental & Water Treatment

Desalination Plants: Reverse osmosis (RO) system components and brine handling pipes (tube/pipe) — resists seawater and concentrated brine corrosion.

Mining: Slurry transport pipes (tube/pipe) and leaching tanks (plate) — withstands acidic mining fluids (e.g., copper leaching with sulfuric acid).

Aerospace & Defense

Aerospace Fuel Systems: Fuel lines (tube) and tank liners (sheet) — resists corrosion from jet fuel additives and atmospheric moisture.

Military Vessels: Seawater cooling systems (tube/pipe) and hull components (plate) — withstands marine corrosion and biofouling.

Specialized Applications by Form

Wire: Welding filler metal for joining C276 components in chemical plants; precision heating coils in corrosive furnaces.

Tube/Pipe: Corrosive fluid transport (acid lines, sour gas pipelines) and heat exchanger tubes in power plants.

Plate/Sheet: Large-scale storage tanks for aggressive chemicals and reactor vessels in pharmaceutical manufacturing.

Forging Stock: Heavy-duty pump casings and valve bodies for high-pressure, high-corrosion process streams.

In summary, Alloy C276 (Hastelloy C276, UNS N1276) — available in forms from Bar and Wire to Plate and Forging Stock — sets the standard for corrosion resistance across diverse harsh environments. Its unique chemical composition and versatile product forms make it an irreplaceable material in chemical processing, oil & gas, power generation, and beyond, where reliability and corrosion resistance are non-negotiable.

Packing of Standard Packing: 

Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 1051 gallon liquid totes Special package is available on request.