Austenitic Heat resistant stainless steel

309 and 310 stainless sheets of steel are heat-resistant austenitic steels characterized by high Cr and Ni content. 309S and 310S are their low carbon versions respectively. In oxidizing media, they both have excellent corrosion resistance and high-temperature strength. At room temperature, the matrix microstructure of austenitic stainless steel 310 is pure γ. 310 is also known as “2520 stainless steel” because it contains 25% chromium and 20% nickel, respectively. 310S and 309S are not easy to oxidize at high temperature and are commonly used high-temperature resistance grades. The experimental results show that the oxidation rate of 310 is slow when the temperature is less than 1000℃. As the temperature continues to rise to 1200℃, the degree of oxidation of 310 accelerates rapidly. In addition, they are also used in the transport and storage of strong acids such as nitric acid with a concentration of 65% ~ 85%.


Alternative material in other standards:

JIS G4303 SUS 309S, SUS 310S

EN 10088-1 X12CrNi23-13/ 1.4833, X15CrNiSi25-21/1.4841, X8CrNi25-21/ 1.4845


Chemical Composition

ASTM 309 309S 310 310S
C ≤0.20 ≤0.08 ≤0.25 ≤0.08
Si ≤1.00 ≤1.00 ≤1.50 ≤1.50
Mn ≤2.00 ≤2.00 ≤2.00 ≤2.00
P ≤0.045 ≤0.045 ≤0.045 ≤0.045
S ≤0.030 ≤0.030 ≤0.030 ≤0.030
Cr 22.00~24.00 22.00~24.00 24.00~26.00 24.00~26.00
Ni 12.00~15.00 12.00~15.00 19.00~22.00 19.00~22.00

Under the high temperature condition, 310 heat resistant stainless steel can keep the performance is stable, not easy to be corroded and oxidized by the outside. This is mainly due to the high Cr content in 310 stainless steel itself, metal Cr can combine with oxygen to form Cr2O3 oxide film, which constantly covers the surface of 310 steel until all the package, equivalent to 310 steel put on the “protective clothing”, which can prevent the internal 310 metal contact with the outside world, This is the main reason why 310 steel can have good oxidation resistance at high temperature.

For heat-resistant stainless steel, the chromium (Cr) element is stable at high temperature, does not occur oxidation and falls off. But the content of Cr can not be too high, otherwise, the toughness of stainless steel will also decline because Cr can promote the emergence of α composition and inhibit γ, too much α is easy to lead to the generation of brittle phase. Therefore, in austenitic stainless steel, we hope that the content of Cr remains moderate, which can not only ensure the performance of the material in all aspects but also prevent the emergence of some brittle phases.

Nickel is a very important element in heat-resistant austenitic stainless steel and plays an active role in promoting the formation of γ. The increase of Ni content can make the transition temperature from γ to αphase become very low, which can enhance the stability of the austenite matrix. In addition, appropriate Ni content can obviously improve the overall mechanical properties and good welding properties of stainless steel.