UNS S30908 (309S) Stainless Steel Forgings
Forged rings, seamless rolled rings, flanges, round bars, discs, sleeves, shafts and tube sheets produced to ASTM A473 by Jiangyin Jiangnan Metal Co., Ltd.
UNS S30908 is the UNS number for AISI 309S, a heat-resistant austenitic stainless steel with 22 to 24 % chromium, 12 to 15 % nickel and 0.08 % carbon maximum. It is the low-carbon version of type 309. The reduced carbon limits carbide precipitation and improves weldability, while the high chromium and nickel give oxidation resistance to about 1038 °C (1900 °F) in non-cyclic service. The grade is specified for high-temperature oxidation and scaling resistance rather than for wet or chloride corrosion. ASTM A473 is the governing specification for 309S forgings.
- UNS
- S30908
- AISI / ASTM
- 309S
- EN / W-Nr.
- 1.4833
- JIS
- SUS 309S
- Structure
- Austenitic
- Max. oxidation
- 1038 °C
1. What UNS S30908 (309S) is
UNS S30908 is a chromium-nickel austenitic stainless steel used in elevated-temperature service. Its chromium content of 22 to 24 % and nickel content of 12 to 15 % are well above those of 304, so it forms a more protective and more adherent oxide scale. That is why it appears in furnace internals, thermal-processing hardware and combustion equipment rather than in general corrosion duty.
The S suffix marks the low-carbon variant. Type 309 permits up to 0.20 % carbon. Type 309S caps carbon at 0.08 %, which holds back chromium-carbide precipitation at grain boundaries and gives better weldability. Type 309H (UNS S30909) runs carbon higher for improved creep resistance. Selecting between the three is a trade-off between weldability and creep strength.
2. Chemical composition of UNS S30908
| Element | Min. | Max. |
|---|---|---|
| Carbon (C) | - | 0.08 |
| Chromium (Cr) | 22.0 | 24.0 |
| Nickel (Ni) | 12.0 | 15.0 |
| Manganese (Mn) | - | 2.00 |
| Silicon (Si) | - | 1.00 |
| Phosphorus (P) | - | 0.045 |
| Sulfur (S) | - | 0.030 |
| Iron (Fe) | Balance, roughly 58 to 66 % | |
Silicon is worth watching. ASTM A473 and the general 309S composition allow up to 1.00 % Si, while some published datasheets quote a tighter 0.75 % maximum. If your design depends on the silicon window, for example where scale adherence under cycling matters, state the limit on the purchase order and we will melt to it.
3. Mechanical properties
| Property | ASTM A473 minimum | Typical annealed value |
|---|---|---|
| Tensile strength, Rm | 515 MPa (75 ksi) | 580 to 620 MPa |
| Yield strength, Rp0.2 | 205 MPa (30 ksi) | 230 to 310 MPa |
| Elongation, A | 40 % | 42 to 45 % |
| Reduction of area, Z | 50 % | about 51 % |
| Hardness | - | about 84 HRB / 190 HB |
| Fatigue strength | - | about 210 MPa |
4. Physical and thermal properties
| Property | Metric | Imperial |
|---|---|---|
| Density | about 8.0 g/cm³ | 0.289 lb/in³ |
| Melting range | 1370 to 1420 °C | 2500 to 2580 °F |
| Modulus of elasticity | 200 GPa | 29 x 106 psi |
| Shear modulus | 78 GPa | 11 x 106 psi |
| Poisson's ratio | 0.27 | |
| Thermal conductivity | 15 W/m·K | 8.7 BTU/h·ft·°F |
| Specific heat capacity | 480 J/kg·K | 0.11 BTU/lb·°F |
| Shear strength | 400 MPa | 58 x 103 psi |
| Max. temperature, mechanical | 1080 °C | 1980 °F |
| Max. temperature, aqueous corrosion | 440 °C | 820 °F |
| PREN | about 23 | |
| Magnetic response | Essentially non-magnetic in the annealed condition | |
Austenitic stainless steels combine high thermal expansion with modest thermal conductivity, and S30908 is no exception. Thick sections therefore need controlled heating and cooling rates. On large rings and tube sheets in this grade, distortion and residual stress usually govern the process, not strength.
5. International equivalent grades
| Standard | Designation |
|---|---|
| USA, UNS | S30908 |
| USA, AISI / ASTM | 309S |
| EN, material number | 1.4833 |
| EN, name | X12CrNi23-13 |
| Japan, JIS | SUS 309S |
| Korea, KS | STS 309S |
| China, GB | 06Cr23Ni13, formerly 0Cr23Ni13 |
| UK, BS | 309S16 / 309S24 |
| France, NF | Z15CN 23-13 |
| Russia, GOST | 10Kh23N13 |
| ISO | X12CrNi23-13 |
6. Applicable product standards
| Product form | Specification | Scope |
|---|---|---|
| Forgings | ASTM A473 | Stainless steel forgings for general use and for low or high-temperature service. Covers grade 309S, UNS S30908 |
| Bars and shapes | ASTM A479 / A479M | Hot and cold-finished bars for boiler and pressure-vessel construction. Includes S30908 |
| Plate, sheet, strip | ASTM A240 / ASME SA-240 | Chromium and chromium-nickel plate for pressure vessels and general applications |
7. Forging, hot working and heat treatment
Melting
We melt UNS S30908 by EAF plus VOD, with ESR remelting available where cleanliness, segregation control or ultrasonic acceptance criteria call for it. That generally applies to heavy rings, rotating parts and anything carrying an EN 10228-3 or ASTM A388 requirement.
Hot working
309S is hot worked at approximately 1177 °C (2150 °F) and reheated at 982 °C (1800 °F), then cooled rapidly to restore maximum corrosion resistance. Finishing too cold leaves work hardening in the part. Finishing too hot coarsens the grain and costs impact toughness.
Annealing
Solution annealing runs between 1038 °C and 1121 °C (1900 to 2050 °F) followed by a water quench. The quench matters. Slow cooling through the sensitisation range re-precipitates carbides and gives away the main reason for specifying the low-carbon grade.
Cold working and machining
The alloy can be drawn, headed, upset and stamped, but it work hardens quickly and should be fully annealed afterwards to relieve internal stress. Machinability is broadly similar to 304: rigid setups, sharp tooling, positive feed, no dwelling.
Welding
309S welds by most resistance and fusion processes. Oxyacetylene welding is not recommended. The low carbon level is what makes multi-pass and repair welding practical in this grade.
8. UNS S30908 forged shapes we produce
- Seamless rolled rings and forged rings. Ring-rolled for continuous circumferential grain flow. Retaining rings, furnace rings, burner rings, bearing races.
- Forged flanges. Weld neck, slip-on, blind, long weld neck, orifice and special-bore flanges, machined or rough turned.
- Round bars, square bars and billets. Peeled, rough turned or black forged.
- Discs, disks and blanks. Upset-forged solid discs and gear blanks.
- Sleeves, bushings and hollow forgings. Trepanned or mandrel-forged bores.
- Forged tubes and forged pipe. Heavy-wall and short-run sizes that are not economic in seamless.
- Tube sheets and plate forgings. For heat exchangers and recuperators.
- Shafts, spindles and stepped shafts, including eccentric and crankshaft-type open-die work.
- Valve components. Bodies, bonnets, stems, seat rings and blocks for ball, gate, globe, check and plug valves.
- Nozzles, manifolds, rolls and custom open-die parts forged to drawing.
Send a drawing, or simply the outside diameter, inside diameter, height and quantity. For rings we quote both the rolled-ring route and the open-die route so the cost difference is visible before you commit.
9. Where UNS S30908 forgings are used
Thermal processing
Annealing covers and boxes, burner grids, furnace doors, fans, lead pans, neutral salt pots, muffles, retorts, recuperators and walking beams.
Furnace and boiler internals
Oven linings, boiler baffles, fire box sheets, furnace components and high-temperature containment parts.
Waste treatment
Incinerator and thermal oxidiser hardware exposed to cyclic high heat.
Petroleum refining
Catalytic recovery systems and recuperators working in the high-temperature oxidising range.
Power generation
Burner hardware, tube hangers and furnace grids in coal-fired and fluidised-bed plant.
Pulp, paper and process plant
Paper mill equipment, plus chemical and pharmaceutical process hardware running above the comfortable range of 304 and 316.
10. Design limitations to check before specifying
Oxidation ceiling. 309 and 309S resist oxidation up to about 1038 °C (1900 °F) in non-cyclic service. Frequent thermal cycling brings that down to roughly 1010 °C (1850 °F), and the destructive scaling temperature sits near 2000 °F. Cycling, rather than peak temperature, is what usually ends the life of these parts.
Sigma-phase embrittlement. Long exposure in the range of roughly 650 to 950 °C can embrittle 309-type grades through sigma-phase formation. Where a component sits in that window, allow for a solution-anneal recovery step or move to a grade less prone to sigma formation.
Creep. 309S is generally credited with creep resistance to around 700 °C. Above that, base load-bearing design on 309H (S30909) or on nickel alloys such as Incoloy 800H and 800HT, Inconel 617 or Haynes 230.
Not a wet-corrosion grade. With a PREN of about 23 and a maximum aqueous-corrosion service temperature near 440 °C, S30908 is the wrong choice for seawater, chloride, sour or strong-acid duty. For those conditions look at A182 F51, F53, F55, 904L, F44 or Alloy 20. Tell us the service conditions and we will say which of them fits.
11. Testing, inspection and certification
- Chemical analysis. Ladle and product analysis by spectrometer, reported element by element.
- Mechanical testing. Tensile, yield, elongation, reduction of area, hardness and impact as required by ASTM A473 or by the customer specification.
- Ultrasonic testing. To EN 10228-3, SEP 1921, ASTM A388 or an agreed acceptance class.
- Other NDT. Liquid penetrant plus visual and dimensional inspection. Magnetic particle testing does not apply to this austenitic grade.
- Intergranular corrosion testing. ASTM A262 practice on request.
- Certification. EN 10204 type 3.1 as standard, or type 3.2 witnessed by a third party such as TUV, SGS, BV, LR or DNV.
- Traceability. Heat number hard-stamped and recorded through every processing stage.
12. Frequently asked questions
What is UNS S30908?
UNS S30908 is the Unified Numbering System designation for AISI 309S, a high-chromium, high-nickel heat-resistant austenitic stainless steel containing 22 to 24 % chromium, 12 to 15 % nickel and 0.08 % carbon maximum. The controlled carbon level limits carbide precipitation and improves weldability compared with standard type 309.
What is the difference between 309, 309S and 309H?
Carbon content. Type 309 (S30900) allows up to 0.20 % C. Type 309S (S30908) caps carbon at 0.08 % for better weldability. Type 309H (S30909) carries higher carbon for improved creep resistance. All three sit at roughly 23 % Cr and 14 % Ni.
What is the maximum service temperature of UNS S30908?
About 1038 °C (1900 °F) for oxidation resistance under non-cyclic conditions. Frequent thermal cycling reduces that to around 1010 °C (1850 °F), and destructive scaling begins near 2000 °F. Separately, long exposure between about 650 °C and 950 °C risks sigma-phase embrittlement, and creep resistance is normally cited only to around 700 °C.
Which standard governs UNS S30908 forgings?
ASTM A473, Standard Specification for Stainless Steel Forgings, covers grade 309S / UNS S30908 with annealed minimums of 515 MPa tensile, 205 MPa yield, 40 % elongation and 50 % reduction of area. ASTM A479 covers bars and shapes, ASTM A240 covers plate. ASTM A182 F309H and A965 F309H are 309H (S30909), a different grade.
What are the EN, JIS and GB equivalents?
EN 1.4833 / X12CrNi23-13, JIS SUS 309S, KS STS 309S, GB 06Cr23Ni13, BS 309S16 and 309S24, NF Z15CN23-13 and GOST 10Kh23N13. Equivalents are approximate, so name the governing standard on the order where it matters.
Can UNS S30908 be used in seawater or chloride service?
No. Its PREN is only about 23 and its useful aqueous-corrosion temperature is around 440 °C. It is an oxidation-resistance grade. Duplex, super-duplex and super-austenitic grades are the right choice for chloride, seawater and sour environments.
What sizes and weights can you forge in S30908?
We produce open-die forgings and seamless rolled rings to customer drawings. Achievable size depends on geometry, reduction ratio and testing requirements, so send the drawing or the OD, ID and height, and we will confirm feasibility, weight and lead time, normally within 24 hours.
Who supplies UNS S30908 forgings?
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, manufactures UNS S30908 / 309S forged rings, rolled rings, flanges, bars, discs, sleeves, shafts and tube sheets, supplied with EN 10204 3.1 or 3.2 certification. Telephone +86-189-2135-9659, email sales@steelforgepieces.com.
Request a Quotation for UNS S30908 Forgings
Send the drawing, or just the dimensions, grade and quantity. We reply with price, weight, lead time and the applicable test plan, usually within one working day.
Open-Die Forging Factory
Related grades we forge
Published by Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China. Last technical review . Data compiled from ASTM A473, ASTM A240 and A479 published grade data and mill datasheets. Values are for guidance. Certified results are issued per heat on the EN 10204 certificate.