Properties of Alloy 31

Chemical analysis of Alloy 31

Designated as UNS N08031 or DIN W.Nr. 1.4562, Alloy 31 is an iron-nickel-chromium-molybdenum alloy with nitrogen and copper additions which has hybridized properties of austenitic super stainless steels and regular nickel alloys. Alloy 31 has exceptional corrosion resistance to alkaline & halide-containing media, sulfuric acid, phosphoric acid, chlorine dioxide media, nitric acid as well as reducing & oxidizing medias. It is widely used in offshore & marine industries, chemical & petrochemical processing, pharmaceutical piping, oil and gas extraction, and ore digestion plants. Especially, Alloy 31 can be used for the fabrication of pressure vessels which may endure a wide temperature-range from cryogenic level to elevated temperatures(-196°C to 550 °C).

Alloy 31 is an iron-nickel-chromium-molybdenum alloy with relatively low cost and high corrosion resistance. Nitrogen and copper are added to this alloy element, and its performance is between special alloy austenitic stainless steel and existing nickel-based alloys.  Alloy 31 has excellent general corrosion resistance to alkaline and halide-containing media, sulfuric acid, phosphoric acid, chlorine dioxide media, nitric acid, and reducing and oxidizing media. It also has excellent resistance to intergranular corrosion, pitting corrosion, and crevice resistance. Corrosion and stress corrosion resistance and other local corrosion performance. This alloy has good cold and hot workability, formability, welding performance, high strength, and good plasticity. It is one of the iron-nickel-based corrosion-resistant alloys with the best overall performance.

Chemical Composition Requirements

Features of Alloy 31

Alloy 31 nickel-based alloy is a nitrogen-containing iron-nickel-chromium-molybdenum alloy. Face-centered cubic lattice structure. The 0.2% nitrogen content stabilizes the austenite phase and reduces the tendency of intermetallic phase precipitation. The performance is between the super austenitic stainless steel and the existing nickel-based alloy. The chemical composition of Alloy31 makes it very resistant to halide corrosion. At the same time, the alloy also has excellent corrosion resistance to pure or impure sulfuric acid at various concentrations and temperatures. It has good corrosion resistance in a small amount of aerated industrial sulfuric acid.

Corrosion resistance

UNS N08031 has excellent corrosion resistance and performs well in a variety of highly corrosive environments. The alloy has good corrosion resistance to oxidizing media, reducing media and mixed media, including sulfuric acid, hydrochloric acid, nitric acid, chloride, ammonia water, sea water, etc. In addition, Alloy 31 alloy also has excellent resistance to stress corrosion cracking, especially suitable for corrosive environments under high temperature and high pressure.

High temperature resistance

Alloy 31 alloy has good high temperature resistance, and can maintain good mechanical properties and corrosion resistance at high temperatures. The alloy can be used at temperatures up to 1100°C and still has good strength, ductility and toughness at high temperatures. In addition, the alloy has excellent oxidation resistance and can perform well in high temperature oxidizing environments.

Machining

Alloy 31 alloy can be processed in a variety of ways, including milling, turning, drilling and cutting. Due to the high hardness and toughness of this alloy, it is necessary to use high-quality cutting tools and machine equipment in the machining process to obtain good processing results.

Welding

Alloy 31 alloy can be used for various welding, including TIG welding, MIG welding and arc welding. In the welding process, it is necessary to use welding consumables that match Alloy 31 to ensure the corrosion and mechanical properties of the welded joint. Recommended welding materials include Alloy 31 welding wire and Alloy 31 solder, etc. During the welding process, attention needs to be paid to controlling the welding temperature and welding speed to avoid excessive residual stress and stress corrosion cracking.

Heat treatment

Alloy 31 alloy can be subjected to various heat treatments, including annealing and solution treatment. The solution treatment temperature is 1050-1150°C, and the holding time is 1-2 hours; the annealing treatment temperature is 950-1050°C, and the holding time is 1-2 hours. These heat treatments improve the alloy's grain structure, increase hardness and strength, and reduce residual stress and the risk of stress corrosion cracking.

Applications for Alloy 31

Alloy 31 alloy has excellent corrosion resistance and high temperature resistance, so it is suitable for a variety of industrial fields, including:

1. Chemical industry: used in the manufacture of chemical reactors, distillation towers, pipelines and pumps and other equipment.

2. Petrochemical industry: used in the manufacture of oil well casings, oil and gas pipelines, storage tanks and reactors and other equipment.

3. Marine engineering: used to manufacture seawater desalination equipment, seawater coolers, seawater pumps and equipment on offshore platforms.

4. Sewage treatment: used to manufacture sewage treatment equipment, including sewage treatment reactors, sewage treatment pumps, sewage treatment pipelines and sludge drying equipment, etc.

5. Others: Alloy 31 alloy is also suitable for the manufacture of food processing equipment, pharmaceutical equipment, power equipment and nuclear power equipment.