High-Performance austenitic stainless steels: The more highly alloyed austenitic grades are often termed High-Performance austenitic stainless steels. These steels have increased levels of chromium, nickel, molybdenum, and occasionally nitrogen and are designed to provide increased resistance to aggressive environments such as stronger acids, bases, and higher chloride-bearing environments including seawater, brackish water and brines. A copper addition used in the 904L (N08904) and alloy 20 (N08020) stainless steels provides improved resistance to reducing acids. As a group, the High-Performance grades also tend to have higher strength levels and improved resistance to stress corrosion cracking compared to the 300 and 200 Series stainless steels.
The 6% Mo super austenitic stainless steels, which include the grades UNS N08367, S31254, and N08926, contain approximately 20% chromium, 6% molybdenum, and 0.20% nitrogen. These grades show very good resistance to various chemical environments and can resist long-term exposures to seawater. In many environments, 6% Mo grades have a corrosion resistance that is just below that of the Ni/Cr/Mo alloys such as 625 (N06625) and C276 (N10276).
The most corrosion resistant austenitic stainless steels are the 7% Mo grades UNS S32654, S31277 and N08354, which have a resistance in many environments that approaches the C276 (N10276) alloy.
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