Stainless steel duplex stainless steels are achieved with an overall lower alloy content than similar-performing super-austenitic grades, making their use cost-effective for many applications. Duplex grades are characterized into groups based on their alloy content and corrosion resistance. Precipitation hardening stainless steels have corrosion resistance comparable to austenitic varieties, but can be precipitation hardened to even higher strengths than the other martensitic grades. The most common, 17-4PH, uses about 17% chromium and 4% nickel. The designation "CRES" is used in various industries to refer to corrosion-resistant steel. Most mentions of CRES refer to stainless steel, although the correspondence is not absolute, because
Marine grade stainless Marine grade stainless Marine grade stainless steel is a misunderstood description. There is no industry recognized definition for a marine grade stainless steel though it is routinely used by many end-users. In a marine environment it must be made clear as to whether the stainless steel is submerged in seawater or is simply near enough to the seashore such that it can be attacked by the chloride present in seawater by splashing or carried by onshore breeze. Chloride ions can cause localized corrosive attack (pitting and crevice corrosion) of susceptible stainless steels. When submerged a stainless steel with a PREN