Stainless 431 / AISI 431Stainless 431 offers the best corrosion resistance of the conventional martensitic stainless grades. Stainless 431 has the best corrosion resistance to marine atmospheres, also resists attack by many petroleum products and organic materials, and several acidic environments. Available forms are seamless pipe, welded pipe, seamless tube, welded tube, bar, wire, sheet, plate, forgings, pipe fittings and flanges.