What is the composition of 309 stainless steel?
Element	Content (%)
Iron, Fe	60
Chromium, Cr	23
Nickel, Ni	14
Manganese, Mn	2
Silicon, Si	1
Carbon, C	0.20
Phosphorous, P	0.045
Sulfur, S	0.030

 

Stainless steel 309 Properties	Metric	Imperial
Tensile strength	620 MPa	89900 psi
Yield strength (@ strain 0.200%)	310 MPa	45000 psi
Izod impact	120 – 165 J	88.5 – 122 ft-lb
Shear modulus (typical for steel)	77 GPa	11200 ksi
Elastic modulus	200 GPa	29008 ksi
Poisson’s ratio	0.27-0.30	0.27-0.30
Elongation at break (in 50 mm)	45%	45%
Hardness, Brinell	147	147
Hardness, Rockwell B	85	85
Hardness, Vickers (converted from Rockwell B hardness)	169	169

 

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, SUS 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.

SUS309S (UNS S30908) is the low carbon version of the alloy. It is utilized for ease of fabrication. SUS309H (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.

 

Corrosion Resistance SUS309

SUS 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 intergranular 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.

Alloy 309 resists high temperature corrosion in most in-service conditions. Operating temperatures are as follows:

Oxidizing conditions (max. sulfur content – 2 g/m3)	1922°F (1050°C) continuous service 2012°F (1100°C) peak temperature
Oxidizing conditions (max. sulfur greater than 2 g/m3)	1742°F (950°C) maximum temperature
Low oxygen atmosphere (max. sulfur 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.

 

What is the difference between 309 and 310 stainless?

Type 310 forms a tenacious scale at high temperature and is resistant to spalling and performs better than Type 309 in thermal cycling applications. Type 310 has good sulfidation resistance and good resistance to carburization in moderately carburizing atmospheres.