Grade dossier
309S Stainless Steel for High-Temperature Fabrication
A low-carbon 309 variant used for fabricated furnace and hot-gas components where oxidation resistance, weldability and thermal cycling must be assessed together.
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
ASTM A240/A240M flat-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 | 0.08 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
Specified annealed flat-product values
| Tensile strength | 515 MPa min |
|---|---|
| 0.2% yield strength | 205 MPa min |
| Elongation | 40% min |
| Hardness | 95 HRBW max |
Selection indicators
| Density | about 7.8 g/cm3 |
|---|---|
| Producer air-temperature guidance | up to about 1000°C / 1830°F; not a design allowable |
| Thermal expansion | Higher than ferritic steels |
| Heat treatment | Not hardened by thermal treatment |
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 309S 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 baffles, liners and annealing boxes
Thermowells and hot-gas components
Fabricated heat-treatment equipment
Oxidizing high-temperature service after atmosphere review
Reasons to stop and review
Using an oxidation guideline as a load-bearing design temperature
Sulfurous, carburizing or reducing atmospheres without specialist review
Wet chloride service chosen only from chromium content
Confusing 309S with 309 or 309H
Fabrication route
Protect properties through cutting, forming and welding
Use temperature-dependent code allowables and creep data.
Allow for thermal expansion, cycling and distortion.
Choose filler and heat input for the base metal, atmosphere and joint.
Prevent condensate traps during shutdown.
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.
Cold-rolled coil, strip and sheet
Hot-rolled coil, strip and plate
Quarto plate
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.
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Interactive selection check
Test 309S against the controlling question
Procurement FAQ
Questions to close before placing the order
Is 309S stainless steel magnetic?
Magnetic response depends on microstructure and delivered condition.
Can 309S 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?
Not automatically. The values shown use flat-product requirements as a reference. Other forms can use different product standards, dimensions and tests.
What should a 309S 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
ASTM A240/A240M requirements for UNS S30908 flat product
Outokumpu Therma 309S/4833 official datasheet
ASTM A959 harmonized wrought-grade composition
Applicable ASME design-code allowables for the actual product and temperature