309/309S Stainless Steel

General Properties

Alloys 309 and 309S are austenitic chromium-nickel stainless steels that are often used for higher temperature applications. Due to their high chromium and nickel content, Alloys 309 and 309S are highly corrosion resistant, have outstanding resistance to oxidation, and excellent heat resistance while providing 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.

Specifications: UNS S30900/S30908

Applications:

Alloys 309 and 309S are used exclusively for their high temperature oxidation resistance, excellent high temperature strength, along with their resistance to creep deformation and environmental attack. Some examples include, but are not limited to:

• Heating elements
• Aircraft and jet engine parts
• Heat exchangers
• Carburizing annealing products
• Sulfite liquor handling equipment
• Kiln liners
• Boiler baffles
• Refinery and chemical processing equipment
• Auto exhaust parts

Standards:

• ASTM/ASME: UNS S30900/S30908
• EURONORM: FeMi35Cr20Cu4Mo2
• DIN: 2.4660

Corrosion Resistance

• Provide excellent corrosion resistance
• More resistant to marine atmospheres than Alloy 304
• Often used at higher temperatures to take advantage of their oxidation resistance
• Have high resistance to sulfite liquors
• Generally considered heat resistant alloys
• Destructive scaling temperature is approximately 2000^oF
• Good scaling resistance with regard to continuous and intermittent service

 High Temperature Corrosion

Heat Treatment

• Cannot be hardened through heat treatment because the consist solely of austenite at room temperature
• Higher tensile and yield strengths that can be obtained through cold working and not followed by full annealing are not stable at the higher temperatures where these alloys are used
• Creep properties can be negatively affected by the use of cold worked material at these higher temperatures

Fabrication

• Can be roll formed, stamped, and drawn readily
• In process annealing is often required to reduce hardness and increase ductility

Weldability

• The austenitic class of stainless steels is generally considered to be weldable
• Generally considered to have weldability equivalent to the most common alloys of the austenitic class 304 and 304L
• Special consideration is needed to compensate for a higher coefficient of thermal expansion to avoid warping and distortion

Chemical Properties:

Mechanical Properties:

Physical Properties: