Article
Grades 309 and 310 are the heat-resistant members of the austenitic stainless family. Their high chromium and nickel contents form a tough oxide scale that protects the steel at temperatures where 304 and 316 would scale rapidly.
Composition
| Grade | Chromium % | Nickel % | Carbon % |
|---|---|---|---|
| 304 | 18–20 | 8–11 | 0.08 max |
| 309S | 22–24 | 12–15 | 0.08 max |
| 310S | 24–26 | 19–22 | 0.08 max |
| 310H | 24–26 | 19–22 | 0.04–0.10 |
Temperature capability
- 309 / 309S – good oxidation resistance in continuous service up to about 1000 °C.
- 310 / 310S – oxidation resistance in continuous service up to about 1100 °C, and better under cyclic heating.
The S versions have lower carbon to reduce sensitisation and improve weldability. The H versions have higher carbon for creep strength.
Applications
- Furnace parts, radiant tubes and burner components
- Heat treatment fixtures, baskets and muffles
- Kiln and incinerator parts
- Hot gas ducts and recuperators
- Dissimilar metal welding (309 filler is widely used to join stainless to carbon steel)
Limitations
Long exposure between about 650 °C and 900 °C can form sigma phase, which reduces toughness at room temperature. 310S is also not a first choice for aqueous corrosion compared with 316L, and its sulphidation resistance is limited in sulphur-rich atmospheres.
Ordering
Pipe 2" SCH 40S, ASTM A312 TP310S, seamless, EN 10204 3.1 – 120 m
Frequently asked questions
What is the maximum temperature for 310S?
It resists oxidation in continuous service up to about 1100 °C, depending on atmosphere and load.
What is the difference between 309 and 310?
310 has more chromium and nickel, giving better oxidation resistance at higher temperatures.
Why is 309 filler used for joining stainless to carbon steel?
Its higher alloy content allows for dilution from the carbon steel while keeping a sound austenitic weld.
Key takeaways
- 309 and 310S are heat-resistant austenitic grades.
- 310S handles higher temperature than 309.
- Watch for sigma phase in long service at 650–900 °C.
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