Alloys 309 and 309S are austenitic chromium-nickel stainless steels that are often used for higher temperature applications. Owing to their high chromium and nickel content, Alloys 309 and 309S are highly corrosion resistant, have exceptional resistance to oxidation, and great heat resistance while offering good strength at room and elevated temperatures. The only significant difference between 309 and 309S is the carbon content, Alloy 309S has a much less carbon composition which minimizes carbide precipitation and improves weldability.
SS 309S stainless steel is a highly alloyed austenitic stainless steel utilized for its outstanding oxidation resistance, high-temperature, strength, and creep resistance. The lower nickel content of Stainless Steel 309, compared to Stainless Steel 310, increases its resistance to hydrogen sulfide (H2S) attack at high temperatures. It is tough and ductile and can be readily fabricated and machined. SS 309S is the low-carbon version, and is recommended for, uses where sensitization and subsequent corrosion by high temperature condensates during shutdown may pose a challenge. Stainless Steel 309S is used for its high-temperature oxidation resistance and resistance to H2S attack. 309S Stainless Steels can be roll formed, stamped and drawn readily. In-process annealing is usually needed to increase ductility and reduce hardness.
309S delivers exceptional general corrosion resistance. It is more resistant to marine atmospheres than Type 304. They display great resistance to sulfite liquors and are used for handling nitric acid, nitric-sulfuric acid mixtures, and acetic, citric, and lactic acids.