Stainless Steel 309
AISI/SAE 309 · UNS S30900 · EN 1.4828, X15CrNiSi20-12 · JIS SUS309
309 (UNS S30900) is a high-chromium, high-nickel (23Cr-13Ni) austenitic heat-resisting stainless steel used where oxidation and scaling resistance above 900 °C is required — furnace parts, radiant tubes, kiln linings, heat-treatment fixtures and boiler baffles.
Values for the Solution Annealed condition
309 tempers and conditions
309 is supplied in 5 conditions, soft to hard. Solution Annealed is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hot Rolled, Annealed and Pickled (plate) | Standard heavy plate condition (ASTM A240 No.1 finish) for furnace hearths, retorts and fabricated heat-resisting structures. | 285 | 590 | 45 | 170 HB | 2.2 % IACS |
mill-annealed sheet/plate condition | General mill-annealed stock (functionally equivalent to solution annealed for this grade); pick for forming and welding fabrication. | 295 | 600 | 45 | 160 HB | 2.2 % IACS |
Solution AnnealedDefault 1040–1150 °C, rapid cool | Standard stocked condition for plate, sheet, bar and pipe; maximum ductility, homogeneous austenite before high-temperature service. | 310 | 620 | 45 | 165 HB | — |
309/309L weld metal deposit | Properties of the all-weld-metal deposit when 309 composition is used as filler for dissimilar-metal, clad-steel and buffer-layer welds. | 400 | 590 | 35 | 190 HB | 2.2 % IACS |
Cold Drawn Bar (lightly cold worked) | Choose for bar/shaft stock needing closer tolerance, better surface and higher strength than annealed; ductility and formability reduced. | 450 | 725 | 30 | 200 HB | — |
Supply forms, finishes and certifications
Ways 309 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
cold_finished | Cold Finished | Surface finish |
hot_finished | Hot Finished | Surface finish |
What is 309?
309 (UNS S30900) is a high-chromium, high-nickel (23Cr-13Ni) austenitic heat-resisting stainless steel used where oxidation and scaling resistance above 900 °C is required — furnace parts, radiant tubes, kiln linings, heat-treatment fixtures and boiler baffles. Its higher alloy content gives better hot strength and sulfidation/oxidation resistance than 304, and the same composition family is widely used as 309/309L filler metal for joining dissimilar and clad steels. Main limits are sigma-phase and carbide embrittlement after long holds in the 600–900 °C range, low room-temperature strength compared with hardenable steels, and poor resistance to chloride pitting relative to Mo-bearing grades. 309 has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,400°C (2,552 °F). 309 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 200 GPa (29 Msi).
What is 309 used for?
- Furnace parts and muffles
- Heat-treatment fixtures and baskets
- Radiant tubes and burner components
- Kiln and furnace linings
- Boiler baffles and supports
- High-temperature exhaust systems
- Dissimilar-metal weld transition pieces
Advantages
- High service temperature — 1,050°C (1,922 °F), better than 91% of stainless steel grades
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 86% of stainless steel grades
- Ductile — tolerates forming and impact — 45%, better than 76% of stainless steel grades
- Forms and bends easily — 68/100, better than 75% of stainless steel grades
Limitations
- High embodied carbon — 6 kg CO₂/kg, worse than 88% of stainless steel grades
309 properties
Typical room-temperature values for 309-Solution Annealed; bars are the position among stainless steel grades.
Physical3
309 has a density of 7.9 g/cm³ (0.285 lb/in³), heavier than 68% of stainless steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
309 has a yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Elongation at break is 45% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
309 is rated for continuous service to 1,050°C (1,922 °F). It conducts heat at 15.6 W/m·K (9.01 BTU/hr·ft·°F), better than 55% of stainless steel grades. Thermal expansion is 14.9 µm/m·K (8.28 µin/in·°F).
Electrical3
309 conducts electricity at 2.2 % IACS, worse than 61% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is good (66/100), better than 59% of stainless steel grades.
Sustainability4
Producing a kilogram of 309 takes about 56 MJ of energy and emits 6 kg of CO₂ — more than 59% of stainless steel grades. Typical recycled content is 60%.
Manufacturability8
309's machinability is fair (36/100, better than 57% of stainless steel grades); weldability very good (70/100); formability good (68/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 309 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 309
Is 309 easy to machine?
Gummy and strongly work-hardening: run rigid setups, positive-rake sharp carbide, 20–30 % lower speed than 304, heavy feed and flood coolant to avoid glazing and work-hardened skins.
Can 309 be welded?
Readily welded by GTAW/GMAW/SMAW with 309/309L filler; no preheat needed, keep interpass low, limit heat input and avoid 600–900 °C holds to reduce sigma-phase and carbide embrittlement.
Can 309 be formed, bent or molded?
Cold forms like 304 but needs about 20 % more power and generous bend radii due to the high work-hardening rate; hot work at 1150–1200 °C followed by solution anneal at 1040–1150 °C.
Manufacturability
The process limits FabDigit applies to 309. Every 309 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair36 / 100 |
|---|---|
| ISO material group | M.1 |
| Cutting speed (rough / finish) | 150 / 180 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1.5 mm |
| Drill depth limit | 4× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better68 / 100 |
|---|---|
| Weldability | Better70 / 100 |
| Bendable | Yes |
309 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C309S (S30908) limits C to 0.08 max | ≤ 0.2 | 0.12 |
| SiEN 1.4828 runs 1.5–2.5 % Si for extra scaling resistance | ≤ 1 | 0.6 |
| Mn | ≤ 2 | 1.4 |
| P | ≤ 0.05 | |
| S | ≤ 0.03 | |
| Cr | 22 – 24 | 23 |
| Ni | 12 – 15 | 13.5 |
| Moresidual only in some specs | ≤ 0.75 | |
| Fe | balance |
What surface finishes work on 309?
Pickle and passivate after hot working or welding to restore the chromium oxide film; can be ground, brushed, electropolished or mirror-polished — not anodizable.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
Organic Coating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 309 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S30900
- EN / DIN / Werkstoff-Nr.
- 1.4828X15CrNiSi20-12
- JIS
- SUS309
- Other
- heat-resisting, high-Si
- Similar grades
- SUH309
How much does 309 cost?
309 is a high-cost stainless steel ($$$$), cheaper than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
309 — frequently asked
What is 309 used for?
309 is typically used for furnace parts and muffles, heat-treatment fixtures and baskets, radiant tubes and burner components, kiln and furnace linings, boiler baffles and supports and high-temperature exhaust systems. In short: high-temperature heat expert.
What is the yield strength of 309?
309 has a typical yield strength of 310 MPa (45 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 63% of stainless steel grades. Strength varies by condition: see the 5 listed tempers.
Is 309 easy to machine?
Not especially — machinability is rated fair (36/100, better than 57% of stainless steel grades). Gummy and strongly work-hardening: run rigid setups, positive-rake sharp carbide, 20–30 % lower speed than 304, heavy feed and flood coolant to avoid glazing and work-hardened skins.
Can 309 be welded?
Yes — weldability is rated very good (70/100). Readily welded by GTAW/GMAW/SMAW with 309/309L filler; no preheat needed, keep interpass low, limit heat input and avoid 600–900 °C holds to reduce sigma-phase and carbide embrittlement.
What surface finishes work on 309?
Pickle and passivate after hot working or welding to restore the chromium oxide film; can be ground, brushed, electropolished or mirror-polished — not anodizable.
Can 309 be formed, bent or molded?
Cold forms like 304 but needs about 20 % more power and generous bend radii due to the high work-hardening rate; hot work at 1150–1200 °C followed by solution anneal at 1040–1150 °C.
What is the maximum service temperature of 309?
309 is rated for continuous use to about 1,050°C (1,922 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 309 cost?
309 is a high-cost stainless steel ($$$$), cheaper than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 309?
Yes — 309 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A240/A240M — Cr and Cr-Ni Stainless Plate, Sheet and Strip — ASTM International (2023)
- ASTM A276/A479 — Stainless Steel Bars and Shapes — ASTM International (2022)
- EN 10095 — Heat resisting steels and nickel alloys (1.4828) — CEN (1999)
- JIS G 4304 / G 4303 (SUS309S) — JISC (2021)
- GB/T 4237 / GB/T 1220 (0Cr23Ni13, 06Cr23Ni13) — SAC (2015)
- ASM Specialty Handbook: Stainless Steels — ASM International (1994)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- 309/309S heat-resisting stainless datasheets (Outokumpu, AK Steel/Cleveland-Cliffs, Sandmeyer) — various producers (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.