309S Stainless Steel (UNS S30908)
Austenitic (heat-resisting) · ASTM A240/A240M · Density 7.9 g/cm³
309S (UNS S30908) is a 23% chromium, 13% nickel heat-resisting austenitic stainless steel. It resists oxidation and scaling to roughly 1000 °C in continuous service, sitting between 304 and 310S in alloy content, and is a workhorse for furnace internals, annealing fixtures and combustion equipment.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | P | S |
|---|---|---|---|---|---|---|
| ≤0.08 | ≤2.00 | ≤0.75 | 22.0–24.0 | 12.0–15.0 | ≤0.045 | ≤0.030 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M.
Mechanical Properties
| Tensile strength | ≥515 MPa (75 ksi) |
|---|---|
| Yield strength (0.2%) | ≥205 MPa (30 ksi) |
| Elongation (50 mm) | ≥40% |
| Hardness | ≤217 HBW |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 7.9 g/cm³ |
|---|---|
| Magnetic response | Essentially non-magnetic after solution annealing; cold work can introduce a measurable magnetic response. |
| Microstructure | Austenitic (heat-resisting) |
Corrosion Resistance & Limits
- 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 & Heat Treatment
| Welding | 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. |
| Machining | 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. |
Equivalent Grades
The closest international equivalents of 309S Stainless Steel are 1.4833 (X12CrNi23-13) in the EN system, SUS309S in the JIS system, 06Cr23Ni13 in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S30908 |
| EN | 1.4833 (X12CrNi23-13) |
| JIS | SUS309S |
| GB | 06Cr23Ni13 |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 309s stainless steel: Sheet / Plate, Coil / Strip, Pipe / Tube, Bar.
| Finishes | No.1, 2B |
|---|---|
| Sheet / coil thickness | 0.5–6.0 mm |
| Plate thickness | 6–50 mm |
Common surface and delivery options: No.1, 2B, BA or mechanically polished finish when supported by the product route; Annealed and pickled, descaled or polished tube finish as specified; Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Furnace parts and radiant tubes
- Heat-treatment baskets and trays
- Kiln and boiler linings
- Combustion chambers and burner parts
- Transition joints between stainless and carbon steel
Frequently Asked Questions
What is the maximum service temperature of 309S?
About 1000 °C in continuous dry-air service and roughly 980 °C in intermittent (thermal-cycling) service. Above that, scaling accelerates and 310S with 25% Cr / 20% Ni is the safer choice.
What is the difference between 309 and 309S?
Only carbon: 309S limits carbon to 0.08% versus 0.20% for straight 309. Lower carbon improves weldability and reduces carbide precipitation; order the S designation explicitly and verify it on the MTC.
309S vs 310S — which should I buy?
310S carries more chromium and nickel, buying roughly 100 °C of extra oxidation resistance (to ~1100 °C continuous) at a noticeably higher price. If your metal temperature stays below ~950–1000 °C, 309S usually does the job at lower cost.
309S Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301316Ti347904L409L4204394414442507303317L254 SMO440C17-4 PH2304
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