Alloy 309 (UNS S30900) is an austenitic stainless steel developed for use in high temperature corrosion resistance applications. The alloy resists oxidation up to 1900°F (1038°C) under non-cyclic conditions. Frequent thermal cycling reduces oxidation resistance to approximately 1850°F (1010°C).

Because of its high chromium and low nickel content, Alloy 309 can be utilized in sulfur containing atmospheres up to 1832°F (1000°C). The alloy is not recommended for use in highly carburizing atmospheres since it exhibits only moderate resistance to carbon absorption. Alloy 309 can be utilized in slightly oxidizing, nitriding, cementing and thermal cycling applications, albeit, the maximum service temperature must be reduced.

When heated between 1202 - 1742°F (650 - 950°C) the alloy is subject to sigma phase precipitation. A solution annealing treatment at 2012 - 2102°F (1100 - 1150°C) will restore a degree of toughness.

309S (UNS S30908) is the low carbon version of the alloy. It is utilized for ease of fabrication. 309H (UNS S30909) is a high carbon modification developed for enhanced creep resistance. It most instances the grain size and carbon content of the plate can meet both the 309S and 309H requirements.

Alloy 309 can be easily welded and processed by standard shop fabrication practices.

Applications

• Furnaces - burners, doors, fans, piping and recuperators

• Fluidized Bed Furnaces - grids, piping, wind boxes

• Paper Mill Equipment

• Petroleum Refining - catalytic recovery systems, recuperators

• Power Generation - pulverized coal burners, tube hangers

• Thermal Processing - annealing covers and boxes, burners grids, doors, fans, lead pans and neutral salt pots, muffles and retorts, recuperators, walking beams

• Waste Treatment - incinerators, rotary kilns and calciners