2205 duplex stainless steel is a widely used duplex stainless steel material, which has excellent comprehensive performance and is widely used in various industrial fields. The following is a detailed introduction to it in English:
Introduction to 2205 Duplex Stainless Steel
2205 duplex stainless steel, also known as UNS S31803 or S32205, is a chromium-nickel-molybdenum duplex stainless steel. It gets its name from its unique microstructure, which consists of approximately 50% austenitic and 50% ferritic phases. This dual-phase structure endows it with superior mechanical properties and corrosion resistance compared to traditional austenitic or ferritic stainless steels.
Chemical Composition
The typical chemical composition of 2205 duplex stainless steel (in weight percentage) is as follows:
- Chromium (Cr): 21.0% - 23.0%
- Nickel (Ni): 4.5% - 6.5%
- Molybdenum (Mo): 2.5% - 3.5%
- Manganese (Mn): ≤2.0%
- Silicon (Si): ≤1.0%
- Carbon (C): ≤0.03%
- Nitrogen (N): 0.08% - 0.20%
- Phosphorus (P): ≤0.03%
- Sulfur (S): ≤0.02%
The balanced composition of chromium, nickel, molybdenum, and nitrogen gives it excellent corrosion resistance and mechanical strength.
Mechanical Properties
2205 duplex stainless steel has high strength and good ductility, and its typical mechanical properties at room temperature are:
- Tensile strength: ≥620 MPa
- Yield strength (0.2% offset): ≥450 MPa
- Elongation at break: ≥25%
- Hardness (HB): ≤290
Compared with austenitic stainless steels (such as 304 or 316), it has about twice the yield strength, which can reduce the thickness of the material used and achieve the purpose of lightweight under the same strength requirements.
Corrosion Resistance
- Pitting and Crevice Corrosion Resistance: Due to its high chromium, molybdenum, and nitrogen content, 2205 duplex stainless steel has excellent resistance to pitting and crevice corrosion. Its pitting corrosion resistance equivalent number (PREN) is usually above 32 (calculated by the formula: PREN = %Cr + 3.3×%Mo + 16×%N), which is much higher than that of 316L stainless steel.
- Stress Corrosion Cracking (SCC) Resistance: The dual-phase structure makes it have better resistance to SCC in chloride environments than austenitic stainless steels. It can be used in environments where traditional austenitic stainless steels are prone to SCC, such as seawater, brine, and chemical process fluids.
- General Corrosion Resistance: It also has good resistance to general corrosion in many acidic and alkaline media, such as dilute sulfuric acid, phosphoric acid, and various organic acids.
Fabrication and Welding
- Hot and Cold Working: 2205 duplex stainless steel can be hot-formed or cold-formed, but cold working will increase its strength and hardness and reduce its ductility. Appropriate annealing treatment may be required after severe cold working to restore its ductility and corrosion resistance.
- Welding: It can be welded by common welding methods, such as tungsten inert gas welding (TIG), metal inert gas welding (MIG), and shielded metal arc welding (SMAW). During welding, it is necessary to pay attention to controlling the heat input to avoid excessive grain growth and the formation of harmful phases, which may affect its mechanical properties and corrosion resistance. Post-weld heat treatment is usually not required, but rapid cooling after welding is recommended to maintain the balance of the dual-phase structure.
Applications
Due to its excellent properties, 2205 duplex stainless steel is widely used in the following fields:
- Oil and Gas Industry: Used for offshore platforms, pipelines, valves, pumps, and other equipment, which need to withstand the corrosion of seawater and acidic media.
- Chemical and Petrochemical Industry: Applied to reactors, heat exchangers, tanks, and pipelines for handling corrosive chemicals.
- Marine Engineering: Used in shipbuilding, seawater desalination equipment, and marine structures.
- Paper and Pulp Industry: Used in equipment exposed to bleaching agents and other corrosive substances.
- Construction and Architectural Applications: For decorative components and structural parts in harsh environments.
- Power Generation: Used in power plant equipment, especially in systems involving wet flue gas desulfurization.
Standards and Specifications
2205 duplex stainless steel complies with various international and national standards, including:
- ASTM A240 / A240M
- EN 10088-2
- ASME SA-240
- ISO 683-13
These standards specify the chemical composition, mechanical properties, and testing requirements of the material to ensure its quality and consistency.
In summary, 2205 duplex stainless steel is a high-performance engineering material. Its unique dual-phase structure makes it have a perfect balance of strength, corrosion resistance, and processability, making it an ideal choice for many demanding industrial applications.
