Technical center

309S Stainless Steel Pipes and Tubes

Alloys 309 and Alloys 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.

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. Specifications: UNS S30900 / S30908


Element

309

309S

309H

Chromium

22.0 min.-24.0 max.

22.0 min.-24.0 max.

22.0 min.-24.0 max.

Nickel

12.0 min.-15.0 max.

12.0 min.-15.0 max.

12.0 min.-15.0 max.

Carbon

0.2

0.08

0.04 min.-0.10 max.

Manganese

2

2

2

Phosphorus

0.045

0.045

0.045

Sulfur

0.03

0.03

0.03

Silicon

0.75

0.75

0.75

Iron

Balance

Balance

Balance


Properties

Metric

Imperial

Tensile strength, ultimate

620 MPa

89900 psi

Tensile strength, yield (0.2%)

310 MPa

45000 psi

Izod impact

120 - 165 J

88.5 - 122 ft-lb

Modulus of elasticity

200 GPa

29000 ksi

Shear modulus

77 GPa

11200 ksi

Poisson ratio

0.3

0.3

Elongation at break (in 50 mm)

45%

45%

Hardness, Rockwell B

85

85