Alloy C276 (UNS N10276,2.4819,HASTELLOY C-276)
Alloy 276 (UNS N10276,HASTELLOY C-276) is a nickel-molybdenum-chromium-iron-tungsten alloy which is among the most corrosion-resistant alloys currently available. The high molybdenum content imparts resistance to localized corrosion such as pitting. The low carbon minimizes carbide precipitation during welding to maintain resistance to intergranular attack in heat affected zones of welding joints.
Alloy 276 also has good high temperature strength and moderate oxidation resistance although the alloy will eventually form embrittling high temperature precipitates.

General Properties:
Alloy 276 (UNS N10276) is a nickel-molybdenum-chromium-iron-tungsten alloy which is among the most corrosion-resistant alloys currently available. The high molybdenum content imparts resistance to localized corrosion such as pitting. The low carbon minimizes carbide precipitation during welding to maintain resistance to intergranular attack in heat affected zones of welding joints.
Alloy 276 also has good high temperature strength and moderate oxidation resistance although the alloy will eventually form embrittling high temperature precipitates.
Alloy 276 has been available for several years and has been used in ASME Boiler and Pressure Vessel related construction. The alloy is covered in ASME Section VIII Divisions 1 and 2, in numerous product forms.
The alloy is readily fabricated by welding using techniques similar to those used for austenitic stainless steels and other nickel base alloys. Precautions are advisable during fabrication because raising the low carbon and silicon contents of the material may adversely affect important properties.

Characteristics:
HASTELLOY C-276 has outstanding resistance to a wide variety of chemical process environments including ferric and cupric chlorides, hot contaminated mineral acids, solvents, chlorine and chlorine contaminated (both organic and inorganic), dry chlorine, formic and acetic acids, acetic anhydride, sea water and brine solutions and hypochlorite and chlorine dioxide solutions. Alloy C276 also resists formation of grain boundary precipitates in the weld heat affected zone making it useful for most chemical processes in the as-welded condition. It has excellent resistance to pitting and stress corrosion cracking.
HASTELLOY C276 is one of the few alloys resistant to wet chloride gas, hypochlorite and chlorine dioxide solutions.
HASTELLOY C276 has exceptional resistance to strong solutions of oxidizing salts, such as ferric and cupric chlorides.
HASTELLOY C276 is not prone to grain boundary precipitation in the as welded condition and therefore suitable for many chemical process applications

Chemical Analysis:
Typical values (Weight %)
Ni 57.0, Mo 16.0, Cr 15.5, Fe 5.5, W 3.8

Standards:
ASTM........... B 575
ASME.......... SB 575

Formability:
Alloy 276 is capable of being formed like the standard austenitic stainless steels. The material is considerably stronger than conventional austenitic stainless steels and consequently requires higher loads to cause the material to deform. During cold working, the material work hardens more rapidly than austenitic stainless steels. The combination of high initial strength and work hardening rate may necessitate the need for intermediate anneals if the cold deformation is extensive.

Welding:
Alloy 276 has welding characteristics similar to the austenitic stainless steels. When selecting a welding method, techniques that minimize degradation of corrosion resistance should be used. Methods such as gas tungsten-arc welding (GTAW), gas metal-arc (GMAW), shielded metal-arc (coated electrode), or resistance welding do minimal damage to corrosion resistance of the weld and heat affected zone. Oxyacetylene welding should not be used because of probable carbon pick-up from the acetylene flame. Submerged arc fluxes containing carbon or silicon should not be used because they will similarly cause pick-up. Minimum level of heat input consistent with suitable penetration should be conducted to avoid hot cracking.

Heat Treatment:
All Alloy 276 mill products are furnished in the solution heat-treated condition. This consists of heating in the 1900-2100F (1040-1150C) range and rapidly cooling. Alloy 276 should be cooled from solution heat-treatment temperatures to black in two minutes or less for optimum corrosion resistance.
Stress relief heat treatments are not effective, and full anneal should be conducted where stress relief heat treatment of other materials would be considered.
Material to be heat treated should be clean and free of grease, oils, and other potential sources of carbon.

Descaling and Cleaning:
A clean surface is required to obtain the optimum corrosion resistance of Alloy 276.
Surface oxides formed during anneal or welding tend to deplete chromium very close to the scale-base metal interface. For this reason, acid treatments which remove surface metal under scaled surfaces are necessary for optimum corrosion resistance.
The alloy content of the material makes descaling difficult. Stainless wire brushing or grit blasting is advisable, followed by immersion in a mixture of nitric and hydrofluoric acids and a thorough water rinse.

Applications:
Chemical and petrochemical processing
Pulp and paper equipment
Industrial and municipal waste equipment
Air pollution control
Digesters and bleach plants in the paper industry.
Components exposed to sour gas.
Equipment for flue-gas desulfurisation plants.
Evaporators, heat exchangers, filters and mixers used in sulfuric acid environments.
Sulfuric acid reactors.
Organic chloride process equipment.
Equipment for processes utilizing halide or acid catalysts.