Duplex stainless steel grades — 2205, F51, F60, S31803, S32205

What duplex stainless steel is

Standard duplex is 22 % chromium, 5 % nickel, 3 % molybdenum with nitrogen — known as 2205. It exists as two UNS numbers: S31803 (A182 F51), the original, and S32205 (A182 F60), which has tighter, higher minimums for chromium, molybdenum and nitrogen. Most mills now dual-certify S31803/S32205.

• Chromium 21–23 %, nickel 4.5–6.5 %, molybdenum 2.5–3.5 %
• Nitrogen 0.08–0.20 % (S31803) or 0.14–0.20 % (S32205)
• Ferrite content typically 35–55 % in the base metal
• Solution annealed and water quenched

Key properties

Where duplex stainless steel is used

• Offshore oil and gas process piping
• Produced water and seawater-cooled systems
• Chemical tankers and pulp & paper digesters
• Desalination and brine handling
• Higher-strength lines where wall thickness can be reduced

Welding and fabrication

Duplex must be welded with controlled heat input (typically 0.5–2.5 kJ/mm) and over-alloyed nickel consumables (2209) so the ferrite–austenite balance stays in range. Ferrite count, impact testing at −46 °C and ASTM A923 / G48 tests are common project requirements. Avoid long exposure at 300–1000 °C, which forms embrittling sigma and 475 °C phases.