Alloy Steel 309 and 309S are austenitic stainless steel alloys, featuring excellent high-temperature oxidation resistance, corrosion resistance, and mechanical properties. They are widely used in the manufacturing of industrial equipment for high-temperature environments. Here is a detailed introduction to these two alloys:

1. Basic Composition and Standards

309 Stainless Steel:
Typical composition: Approximately 22% Cr, 12% Ni, ≤0.20% C, along with small amounts of Mn, Si, P, S, etc.
Compliance standards: Commonly specified in ASTM A240, ASME SA-240, and similar standards.

309S Stainless Steel:
A low-carbon variant of 309, with a composition similar to 309 but with C≤0.08%. The reduced carbon content minimizes the risk of carbide precipitation during welding or high-temperature service, enhancing resistance to intergranular corrosion.

 

 

 

General Properties

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.

 

 

 

 

 

 

 

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