Introduction to 2205 Stainless Steel
2205 Stainless Steel, a widely used ferritic-austenitic duplex stainless steel, is favored for its combination of high strength and excellent corrosion resistance. Below is a detailed introduction covering its chemical composition, performance characteristics, application fields, and processing methods:
I. Chemical Composition
The chemical composition of 2205 stainless steel is strictly controlled, with the following elements and their roles:
Chromium (Cr) : 21.0%-23.0%. As the core element for corrosion resistance, it forms a passive film on the surface to resist oxidation and corrosion.
Nickel (Ni) : 4.5%-6.5%. Promotes the formation of austenitic phase, enhances toughness and low-temperature performance, and synergizes with chromium to improve corrosion resistance.
Molybdenum (Mo) : 2.5%-3.5%. Strengthens resistance to pitting and crevice corrosion, particularly effective in chloride-containing environments.
Nitrogen (N) : 0.08%-0.20%. Increases strength and corrosion resistance, inhibits the precipitation of harmful phases, and stabilizes the duplex structure.
Carbon (C) : ≤0.03%. The low-carbon design reduces carbide precipitation and lowers the risk of intergranular corrosion.
Manganese (Mn) : ≤2.0%. Assists in austenite formation and improves processability.
Silicon (Si) : ≤1.0%. Enhances oxidation resistance and strength, but excessive content may reduce toughness.
Phosphorus (P) : ≤0.03%. A harmful element that must be strictly controlled to prevent reduced toughness.
Sulfur (S) : ≤0.02%. A harmful element; excessive levels can cause hot working cracking and reduced corrosion resistance.
II. Performance Characteristics
1. Mechanical Properties
High Strength : Tensile strength ≥620MPa, yield strength ≥450MPa, far exceeding that of 304 stainless steel (yield strength ~205MPa), making it suitable for high-pressure and heavy-load scenarios.
Good Toughness : Elongation ≥25% with excellent low-temperature impact performance, maintaining toughness even at -40°C to avoid brittle fracture.
Fatigue Resistance : High fatigue strength, ideal for components subject to long-term alternating loads (e.g., pump shafts, valves).
2. Corrosion Resistance
Resistance to Localized Corrosion : The synergistic effect of chromium, molybdenum, and nitrogen provides outstanding resistance to pitting and crevice corrosion, outperforming 316 stainless steel in seawater and brine environments.
Resistance to Intergranular Corrosion : Low carbon content and stabilizing elements (nitrogen) minimize carbide precipitation. Its intergranular corrosion resistance is verified through sensitization tests (e.g., ASTM A262 Practice E).
Resistance to Stress Corrosion Cracking : The duplex microstructure (40%-60% ferrite, 60%-40% austenite) effectively inhibits stress corrosion, surpassing austenitic stainless steels in chloride-containing environments.
3. Physical Properties
Thermal Expansion Coefficient : Between ferritic and austenitic stainless steels (~12×10⁻⁶/°C), close to carbon steel, reducing thermal stress when joined with dissimilar materials.
Thermal Conductivity : Superior to austenitic stainless steels, ensuring efficient heat dissipation, making it suitable for heat exchange equipment.
III. Application Fields
Oil and Gas Industry : Offshore platform pipelines, oil and gas transmission pipes, and wellhead equipment, resisting corrosion from seawater and corrosive media in oil and gas.
Chemical Industry : Reactors, heat exchangers, and storage tanks for handling corrosive environments such as acids, alkalis, and salt solutions.
Seawater Treatment : Desalination equipment, coastal power plant condenser pipes, and mariculture systems, with excellent seawater corrosion resistance.
Municipal Engineering : Sewage treatment equipment and water supply pipelines (especially in high-chloride areas) to extend service life.
Pulp and Paper Industry : Bleaching equipment and pulp conveying pipes, withstanding corrosion from bleaching agents (e.g., chlorine, chlorine dioxide).
Food Industry : Corrosion-resistant storage tanks and conveying pipes, compliant with food contact standards (e.g., FDA certification).
IV. Processing and Treatment
1. Hot Working
Heating Range : 1050-1200°C, where the duplex structure is uniform and easily formable.
Cooling Requirements : Rapid cooling (e.g., water quenching) after hot working to avoid 475°C embrittlement and σ-phase precipitation (which reduces toughness).
2. Cold Working
Cold rolling and bending are feasible, but higher strength requires greater processing force. Excessive deformation should be avoided to prevent cracking.
Annealing (950-1050°C followed by rapid cooling) is recommended after cold working to restore toughness and corrosion resistance.
3. Welding
Weldability is excellent, with methods such as GTAW (TIG welding) and SMAW (manual arc welding) applicable. ER2209 welding wire or E2209 electrodes are recommended.
Heat input during welding must be controlled to avoid grain coarsening or harmful phase precipitation. Post-weld heat treatment is generally unnecessary for thin parts, but solution treatment is advised for thick sections.
V. Comparison with Other Stainless Steels
Characteristic 2205 Duplex Stainless Steel 304 Stainless Steel 316 Stainless Steel
Yield Strength ≥450MPa ≥205MPa ≥205MPa
Pitting Resistance Excellent (PREN≈33) Moderate (PREN≈18) Good (PREN≈25)
Stress Corrosion Resistance Excellent Poor (especially in chloride environments) Good
Cost Higher Lower Medium-High
(Note: PREN = Pitting Resistance Equivalent Number, calculated as: PREN = Cr% + 3.3×Mo% + 16×N%. Higher values indicate better pitting resistance.)
With its “high strength + high corrosion resistance” combination, 2205 stainless steel is preferred in corrosive environments and high-strength structural applications, often replacing traditional austenitic stainless steels to reduce weight or extend equipment lifespan.