Stainless Steel 309
Stainless Steel 309 (UNS S30900) is an austenitic grade with higher chromium (22-24%) and nickel (12-15%) than the 304 series. This added alloy content gives it much better oxidation resistance, with continuous service temperatures up to 980°C (1800°F).
1. Chemical Composition
The table below lists the elemental ranges for Stainless Steel 309. The higher chromium and nickel levels are what separate it from standard 300 series grades and allow it to handle elevated-temperature service.
| Grade | C | Mn | P | S | Si | Cr | Ni | Mo | Other |
| 309 | = 0.20 | = 2.00 | = 0.045 | = 0.030 | = 1.00 | 22.00–24.00 | 12.00–15.00 | — | — |
2. Mechanical Properties
The table below gives minimum mechanical values for Stainless Steel 309 in the annealed condition. Its higher alloy content helps it retain strength at service temperatures above 600°C.
| Grade | Condition | Tensile Strength Min, MPa (ksi) | Yield Strength Min, MPa (ksi) | Elongation Min, % | Heat Treatment Temp |
| 309 | Annealed | 550 (80) | 205 (30) | 40 | 1040–1150°C (1900–2100°F), Rapid Cool |
3. Equivalent Grade
This table cross-references Stainless Steel 309 designations across ASTM, European, Japanese, Chinese, and Russian standards to support international procurement and specification alignment.
| STANDARD | WERKSTOFF NR. | UNS | JIS | BS | GOST | AFNOR | EN |
| SS 309 | 1.4828 | S30900 | SUS 309 | 309S24 | 20KH20N14S2 | Z17CNS20-12 | X15CrNiSi20-12 |
4. Key Technical Advantages
- High-Temperature Oxidation Resistance: The 22-24% chromium range allows continuous dry-air service to 980°C (1800°F) and intermittent service to roughly 1095°C (2000°F), well above what standard 304 or 316 can handle.
- Elevated Nickel for Structural Stability: The 12-15% nickel range stabilizes the austenitic phase at high temperatures and reduces sigma phase formation during long-term thermal cycling compared to lower-nickel grades.
- Carburization Resistance: The combination of high Cr and Ni gives adequate resistance to carburizing atmospheres at moderate temperatures. This is useful in furnace components and heat treatment fixtures.
- Sulfidation Tolerance: Performs acceptably in mildly sulfidizing atmospheres at moderate temperatures, though it is less resistant than grades with deliberate sulfidation-resistant alloying (e.g., 310).
Technical Note: Grade 309 should not be used in strongly reducing sulfidizing atmospheres at high temperature. For such conditions, evaluate 310 or nickel-base alloys.
5. Common Manufacturing Standards
Stainless Steel 309 is manufactured and inspected in accordance with the following standards:
ASTM A312: Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes — TP309S designation.
ASTM A213: Standard Specification for Seamless Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes — T309S designation.
ASTM A249: Standard Specification for Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes.
ASTM A511: Standard Specification for Seamless Stainless Steel Mechanical Tubing.
DIN EN 10095: Heat-resisting steels and nickel alloys (1.4833).
JIS G4311: Hot-rolled stainless steel bars for heat-resisting applications (SUS309S).
GB/T 1220: Stainless steel bars (20Cr23Ni13).
GOST 5632: High-alloy steels and corrosion-resistant, heat-resistant and heat-treated alloys (20Kh23N13).
Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Pipe | A312 (TP309S) | EN 10095 (1.4833) | G3459 (SUS309S) | 13296 | 5632 |
| Welded Pipe | A312 (TP309S) | EN 10217-7 | G3459 | - | - |
| Heat Exchanger Tube | A213 (T309S) / A249 | EN 10216-5 | G3463 | 13296 | - |
6. Primary Applications
- Industrial Furnace Components: Radiant tubes, muffle liners, and burner nozzles in continuous heat treatment furnaces operating at temperatures up to 980°C.
- Thermal Processing Equipment: Retorts, fixtures, and basket assemblies in annealing, hardening, and brazing furnaces where oxidation scaling needs to be kept to a minimum.
- Waste Incineration Systems: Combustion chamber liners and flue ductwork exposed to high-temperature oxidizing gases that contain chlorides and sulfur compounds.
- Petrochemical Heaters: Tube supports and hangers in fired heaters where skin temperatures regularly approach or exceed what standard austenitic grades can withstand.
- Welding Consumable Base: Grade 309 filler metal and cladding are used to join dissimilar materials (carbon steel to stainless) where a buffer layer with higher alloy content is needed.