309S and 310S stainless steels are high Cr and Ni heat resistant austenitic stainless steels, are the low carbon versions of 309 and 310 respectively. In oxidizing medium, they have both excellent corrosion resistance and high temperature mechanical properties, suitable for high temperature furnace equipment, drying equipment and other key parts, furnace materials, aviation, petrochemical, electric power and so on. Oxidation resistance refers to the ability of heat-resistant steel under high temperature to act for a long time without forming scale or being eroded by medium. Thermal strength refers to the spot steel pipe still has a certain strength under high temperature without a large number of deformation broken.
The Chemical Composition of 309（309S）and 310（310S）
| Grades | C | Si | Mn | P | S | Cr | Ni |
| 309 | 0.20 | 1.00 | 2.00 | 0.045 | 0.03 | 22.0-24.0 | 12.0-15.0 |
| 309S | 0.08 | 1.00 | 2.00 | 0.045 | 0.03 | 22.0-24.0 | 12.0-15.0 |
| 310 | 0.25 | 1.50 | 2.00 | 0.045 | 0.03 | 24.0-26.0 | 19.0-22.0 |
| 310S | 0.08 | 1.50 | 2.00 | 0.045 | 0.03 | 24.0-26.0 | 19.0-22.0 |
The Mechanical Property of 309（309S）and 310（310S）
| Grades | Finish | Tensile strength, min,Mpa | Yield strength, min,Mpa | Elongation in 2in. |
| 309 | Hot finished/Cold finished | 515 | 205 | 30 |
| 309S | ||||
| 310 | ||||
| 310S |
Compared with most superalloys, 309(309S) and 310(310S) offer better resistance to high temperature corrosion. However, stainless steel does not perform as well as 600 alloy (UNS N06600) or 800 alloy (UNS N08800) in thin, nitrated or carbonated air conditions. Due to the perfect combination of high temperature performance and corrosion resistance, 309S and 310S are widely used in high temperature corrosion resistance equipment such as boiler, pressure vessel, metallurgical and petrochemical industry equipment parts, among which 309S can withstand repeated heating below 980℃, 310S service temperature up to 1200℃.
