SMO 254

SMO254 (UNS S31254), a proprietary super austenitic stainless steel developed by Outokumpu, achieves ultra-high corrosion resistance through a high-alloy formulation (≈21% Cr, ≈18% Ni, ≈6.5% Mo, ≈0.2% N). It relies on solid-solution strengthening (no aging/quenching required) to maintain a stable austenitic matrix, exhibiting exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in harsh environments (e.g., seawater, dilute sulfuric acid, chloride solutions). Its performance remains stable in the temperature range of -196 °C to 400 °C; prolonged exposure above 400 °C may trigger σ-phase precipitation, leading to toughness and corrosion resistance degradation. These characteristics make it a core material for corrosion-critical industrial scenarios.

Behaviour that matters in service

• Strengthening Mechanism — Solid-solution strengthening via alloying elements; only solution annealing needed post-fabrication.
• Corrosion Resistance — Excellent pitting/crevice resistance (CPT≥90 °C in 3.5% NaCl), suitable for harsh chemical/marine environments.
• Toughness — Outstanding low-temperature performance (-196 °C impact ≥100 J) for cryogenic applications.
• Processability — Weldable with matching filler; cold-formable; machinability slightly lower than 316L.
• Temperature Limit — Stable up to 400 °C; avoid prolonged exposure above to prevent σ-phase embrittlement.

Typical applications

• Marine/Offshore — Seawater desalination heat exchangers, offshore platform valves.
• Chemical/Petrochemical — Sulfuric acid storage tanks, chlor-alkali process equipment.
• Energy — Oil/gas downhole tubing, geothermal power plant heat exchangers.
• Cryogenic Engineering — LNG storage tank liners, liquid oxygen transport pipes.