2205

2205 (UNS S31803/S32205) is a classic austenitic-ferritic duplex stainless steel, mainly composed of chromium, nickel, molybdenum, and nitrogen. It is renowned for its unique dual-phase structure (~50% austenite + ~50% ferrite), which combines the corrosion resistance of austenitic stainless steel and the high strength of ferritic stainless steel. It exhibits excellent resistance to chloride stress corrosion cracking (SCC), good mechanical properties in a wide temperature range (-50 °C to 300 °C), and high tensile strength (≥620 MPa). These characteristics make it ideal for harsh environments with corrosive media (especially chloride-containing) and high structural load requirements.​.

Behaviour that matters in service

• Excellent Chloride Corrosion Resistance — Outstanding resistance to chloride stress corrosion cracking (SCC) and pitting/crevice corrosion (critical advantage over austenitic steels like 304/316); suitable for seawater, brine, and chloride-containing chemical media.​.
• High Mechanical Strength — Tensile strength (≥620 MPa) and yield strength (≥450 MPa) are 1.5 – 2 times higher than 304/316 stainless steel; reduces component thickness and weight, lowering overall costs.​.
• Balanced Dual-Phase Structure — ~50% austenite + ~50% ferrite ensures good toughness (especially low-temperature toughness, no brittle fracture at -50 °C) and fatigue resistance, avoiding the brittleness of single-phase ferritic steels.​.
• Good Weldability — Compatible with standard welding methods (TIG, MIG, submerged arc welding); controlled heat input (avoiding overheating) maintains post-weld dual-phase balance and corrosion resistance; no need for post-weld heat treatment in most cases.​.
• Medium-Temperature Stability — Maintains stable mechanical properties and corrosion resistance at temperatures up to 300 °C; avoids phase transformation or performance degradation under long-term medium-temperature service.​.

Typical applications

• Seawater Desalination Industry — Widely used in reverse osmosis (RO) membrane housings, seawater intake pipelines, and desalination plant heat exchangers; resists long-term seawater erosion and chloride stress corrosion.​.
• Oil & Gas Industry — Applied to offshore platforms (structural components, pipelines), subsea wellhead equipment, and oilfield chemical tanks; withstands harsh marine environments and corrosive oilfield media (e.g., hydrogen sulfide, chlorides).​.
• Chemical Industry — Used in chloride-containing chemical reactors, acid-resistant pipelines (e.g., hydrochloric acid, sulfuric acid solutions), and fertilizer production equipment; avoids pitting and crevice corrosion in strong corrosive environments.​.
• Municipal & Environmental Engineering — Employed in sewage treatment plants (aeration tanks, sludge pipelines) and waste incineration flue gas treatment systems; resists corrosion from acidic sewage and harmful gases.​.
• Marine Engineering — Used in ship hulls (seawater contact parts), propeller shafts, and marine heat exchangers; combines high strength and seawater corrosion resistance, extending service life of marine equipment.