309S vs 310S Stainless Steel
Side-by-side comparison · Composition · Properties · Selection guide
309S and 310S are heat-resistant austenitic stainless grades. 310S carries more chromium and nickel, giving better oxidation resistance and strength at the upper end of high-temperature service, while 309S is the more economical choice for furnace parts, transition pieces and thermal cycling below that limit.
Full datasheets:309S Stainless Steel·310S Stainless Steel
At a Glance
| 309S | 310S | |
|---|---|---|
| Type | Austenitic (heat-resisting) | Austenitic (heat-resistant) |
| UNS | S30908 | S31008 |
| Standard | ASTM A240/A240M | ASTM A240/A240M |
| Density | 7.9 g/cm³ | 7.98 g/cm³ |
Corrosion Resistance and Service Limits
309S
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
310S
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
Fabrication and Heat Treatment
| Operation | 309S | 310S |
|---|---|---|
| Welding | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. |
| Forming | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. |
| Machining | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. |
| Heat treatment | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. |
Chemical Composition (wt%)
| Element | 309S | 310S |
|---|---|---|
| C | ≤0.08 | ≤0.08 |
| Mn | ≤2.00 | ≤2.00 |
| Si | ≤0.75 | ≤1.50 |
| Cr | 22.0–24.0 | 24.0–26.0 |
| Ni | 12.0–15.0 | 19.0–22.0 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.030 | ≤0.030 |
Mechanical Properties
| Property | 309S | 310S |
|---|---|---|
| Tensile strength | ≥515 MPa (75 ksi) | ≥515 MPa (75 ksi) |
| Yield strength (0.2%) | ≥205 MPa (30 ksi) | ≥205 MPa (30 ksi) |
| Elongation (50 mm) | ≥40% | ≥40% |
| Hardness | ≤217 HBW | — |
| Oxidation resistance | — | up to ≈1050 °C |
Which One Should You Choose?
Choose 309S for:
- Furnace components at moderate high temperature
- Dissimilar welding and transition applications
- Heat shields and kiln parts with cost pressure
- Cyclic service within the qualified temperature range
Choose 310S for:
- Higher-temperature furnace internals
- Oxidizing atmospheres requiring greater scale resistance
- Burner parts, radiant tubes and heat-treatment fixtures
- Applications where the 309S temperature margin is insufficient
Our verdict
Choose 309S when its oxidation and creep performance covers the actual metal temperature; move to 310S when the service needs the extra chromium-nickel margin. Neither grade should be selected by furnace air temperature alone: atmosphere, load, cycling, section and expected creep life all matter.
Cost and Availability
Compare the current stock position, mill route, minimum production quantity, processing yield, testing and delivered cost for 309S and 310S at quotation time. A fixed price ratio would be misleading because product form, size, condition and market timing can change the commercial result.
Do Not Substitute Without Review
Do not replace 309S with 310S, or the reverse, from the grade name alone. Recheck chemistry, mechanical-property condition, product standard, dimensions, corrosion environment, welding procedure and project approval before substitution.
Frequently Asked Questions
Is 310S always better than 309S?
It has a higher temperature capability, but costs more and may offer no benefit below the 309S service envelope. Match the alloy to actual metal temperature and load.
What does the S suffix mean?
It identifies a lower-carbon version used to support weldability and high-temperature fabrication; the exact chemistry remains defined by the material standard.
Can these grades be used in sulfur-bearing atmospheres?
High nickel can be vulnerable in some sulfur environments. Gas chemistry, condensation and cycling require a specialist high-temperature corrosion review.
RFQ
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Technical content updated: 2026-07-29
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.