309 Stainless Steel Data Sheet

Alloy 309 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 sulphur 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 is the low carbon version of the alloy. It is utilized for ease of fabrication. 309 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.

Alloy 309 is not designed for service in wet corrosive environments. The high carbon content, which is present to enhance creep properties, has a detrimental effect on aqueous corrosion resistance. The alloy is prone to inter granular corrosion after long term exposure at high temperatures. However, due to its high chromium content (23%), Alloy 309 is more corrosion resistant than most heat resistant alloys.

High Temperature Corrosion Alloy 309 resists high temperature corrosion in most in-service conditions. Operating temperatures are as follows: Oxidizing conditions (max. sulphur content – 2 g/m3) 1922°F (1050°C) continuous service 2012°F (1100°C) peak temperature Oxidizing conditions (max. sulphur greater than 2 g/m3)   1742°F (950°C) maximum temperature Low oxygen atmosphere (max. sulphur content – 2 g/m3) 1832°F (1000°C) maximum temperature Nitriding or carburizing atmospheres   1562 –1742°F (850 – 950°C) maximum

The alloy does not perform as well as Alloy 600 (UNS N06600) or Alloy 800 (UNS N08800) in reducing, nitriding or carburizing atmospheres, but it does outperform most heat resistant stainless steels in these conditions.