Grade dossier
309 Stainless Steel for High-Temperature Oxidation Service
A high-chromium, high-nickel austenitic grade developed for elevated-temperature oxidation resistance and strength, with atmosphere and thermal cycling controlling real service limits.
Identity before substitution
Define the grade, product and condition together
A familiar grade name is not a complete purchase specification. Product form, controlling standard, dimensions, condition, finish, certification and service environment determine whether the delivered material is suitable.
Composition control
UNS S30900 product chemistry
Limits are not heat analysis targets
The table summarizes grade limits commonly used for plate, sheet and strip. Pipe, tube, bar, forgings and cast products can be governed by different specifications. Always place the product standard and edition on the purchase order.
| C | 0.20 max |
|---|---|
| Mn | 2.00 max |
| Si | 0.75 max |
| P | 0.045 max |
| S | 0.030 max |
| Cr | 22.00-24.00 |
| Ni | 12.00-15.00 |
Properties with context
Minimums, typical indicators and delivered condition
Annealed room-temperature reference values
| Tensile strength | 515 MPa min |
|---|---|
| 0.2% yield strength | 205 MPa min |
| Elongation | 40% min |
| Hardness | 95 HRB max |
Selection indicators
| Density | about 8.0 g/cm3 |
|---|---|
| Primary purpose | High-temperature oxidation resistance |
| Design basis | Atmosphere, cycling, load and section thickness |
| Welded alternative | 309S offers lower carbon for fabrication |
Values depend on product form, thickness, test orientation, condition and governing edition. Use the mill test certificate and the purchase specification for acceptance, not a web table alone.
Selection boundary
Where 309 belongs and where to escalate
Grade selection is an environmental decision, not a popularity contest. Review the complete medium, temperature, geometry, fabrication, cleaning and inspection requirements.
Good reasons to evaluate it
Furnace parts, baffles and heat shields
High-temperature process equipment
Oxidizing hot-gas service after atmosphere review
Components requiring UNS S30900 chemistry
Reasons to stop and review
Treating an oxidation limit as a structural design temperature
Sulfurous, carburizing or reducing atmospheres without specialist review
Confusing 309 with 309S or 309H
Wet chloride service selected only from high chromium content
Fabrication route
Protect properties through cutting, forming and welding
Use creep and allowable-stress data at the actual design temperature.
Select filler and carbon level for the weld and shutdown environment.
Allow for thermal expansion, cycling and distortion.
Remove fabrication contamination before high-temperature service.
Supply definition
Product form changes the applicable requirements
Do not send an RFQ that names only the grade. State form, governing standard, dimensions, tolerances, finish, edge or end condition, quantity, certification and inspection.
Plate, sheet and strip under the specified product standard
Bar and shapes under ASTM A276/A479 as applicable
Wire under ASTM A580 where available
Fabricated furnace and heat-treatment components
Certificate checkpoint
Request heat identity, chemical analysis, mechanical results and compliance to the exact product specification. Add PMI, corrosion testing or supplementary examination only when the application requires it.
Interactive selection check
Test 309 against the controlling question
Procurement FAQ
Questions to close before placing the order
Is 309 stainless steel magnetic?
Magnetic response depends on microstructure and delivered condition.
Can 309 replace another grade?
Only after checking the governing standard, composition, mechanical properties, corrosion exposure, fabrication route and certification. A commercial name is not a substitution approval.
Does the table apply to every product form?
No. Bar, wire, flat product and welded components can use different standards, and 309S/309H are separate UNS grades.
What should a 309 RFQ include?
Product form, standard and edition, UNS or EN designation, dimensions, tolerances, finish, quantity, service, fabrication, certificate and inspection requirements.
Sources, scope and RFQ
Use traceable grade data, then specify the actual product
ATI 309 technical data for UNS S30900
ASTM A959 harmonized composition for wrought stainless steel
Carpenter 309 grade and product-form references
High-temperature stainless design guidance from producer datasheets