1、 Corrosion resistance

Hastelloy C-276 alloy [1] [2] is a tungsten containing nickel chromium molybdenum alloy with very low silicon carbon content. It is considered to be a universal corrosion resistant alloy. It is mainly resistant to wet chlorine, various oxidizing chlorides, chloride solution, sulfuric acid and oxidizing salts. It has good corrosion resistance in low and medium temperature hydrochloric acid. Therefore, in the past three decades, it has been widely used in harsh corrosive environment, such as chemical industry, petrochemical industry, flue gas desulfurization, pulp and paper, environmental protection and other industrial fields.

The alloy has the following characteristics: ① it has excellent corrosion resistance to most corrosive media in oxidation and reduction atmosphere. ② It has excellent pitting corrosion resistance, crevice corrosion resistance and stress corrosion resistance. Higher Mo and Cr contents make the alloy resistant to chloride ion corrosion, and W element further improves the corrosion resistance. At the same time, Hastelloy C-276 alloy is one of the only materials resistant to the corrosion of wet chlorine, hypochlorite and chlorine dioxide solutions. It has significant corrosion resistance to high concentration chloride solutions such as ferric chloride and copper chloride. It is suitable for sulfuric acid solutions of various concentrations. It is one of the few materials that can be applied to hot concentrated sulfuric acid solutions.

2、 Physical properties

The physical properties of Hastelloy C-276 alloy are as follows:

Material composition: 57ni-16cr-16mo-5fe-4w-2.5co * - 1MN * - 0.35v * - 0.08si * - 0.01c*

Executive standard: UNS N10276, ASTM b575, ASME sb575, DIN / en 2.4819 density: 8.90g/cm3

3、 Mechanical properties

Tensile strength: σ B ≥ 730mpa, elongation: δ ≥ 40%, hardness: HRB ≤ 100. The hot forming of Hastelloy C-276 alloy is immediately annealed at 1150 ℃ and quenched with water. Cold deformation of Hastelloy C-276 alloy will increase its strength.

Hastelloy C-276 alloy has similar formability to ordinary austenitic stainless steel. However, due to its greater strength than ordinary austenitic stainless steel, there will be greater stress in the cold forming process. In addition, the work hardening speed of this material is much faster than that of ordinary stainless steel. Therefore, midway annealing should be adopted in the process of extensive cold forming.

4、 Welding and heat treatment

The welding performance of C-276 alloy is similar to that of ordinary austenitic stainless steel. Before using a welding method to weld C-276, measures must be taken to minimize the corrosion resistance of weld and heat affected zone, such as tungsten gas shielded welding (GTAW), metal gas shielded welding (GMAW) Submerged arc welding or other welding methods that can minimize the corrosion resistance of weld and heat affected zone. However, welding methods such as oxyacetylene welding that may increase the carbon content or silicon content of material welds and heat affected zones are not suitable.

For the selection of welding joint form, refer to the successful experience of ASME Boiler and pressure vessel code for Hastelloy C-276 alloy welding joint.

The welding groove is best machined, but machining will bring work hardening, so it is necessary to polish the machined groove before welding.

Appropriate heat input speed shall be adopted during welding to prevent the generation of thermal cracks.

In most corrosive environments, Hastelloy C-276 alloy can be used as weldment. However, in a very harsh environment, C-276 materials and weldments need solution heat treatment to obtain the best corrosion resistance.

The welding of Hastelloy C-276 alloy can choose itself as welding material or filler metal. If it is required to add some components to the welds of Hastelloy C-276, such as other nickel base alloys or stainless steel, and these welds will be exposed to corrosive environment, the welding rod or wire used for welding shall have corrosion resistance equivalent to that of the base metal.

Solution heat treatment of Hastelloy C-276 alloy includes two processes: (1) heating at 1040 ℃ ~ 1150 ℃（ 2) Quickly cool to black state (about 400 ℃) within two minutes, so that the treated material has good corrosion resistance. Therefore, only stress relieving heat treatment of Hastelloy C-276 alloy is invalid. Before heat treatment, clean the oil stain on the alloy surface and all dirt that may produce carbon during heat treatment.

The surface of Hastelloy C-276 alloy will produce oxides during welding or heat treatment, which will reduce the Cr content in the alloy and affect the corrosion resistance, so it is necessary to clean the surface. Stainless steel wire brush or grinding wheel can be used, then immersed in a mixture of nitric acid and hydrofluoric acid in an appropriate proportion for pickling, and finally washed with clean water.

5、 Application field

Petrochemical equipment, heat exchanger, flue gas desulfurization equipment, fluid chemical pump, fluorine chemical industry, etc.