Grade dossier
321H Stainless Steel for Elevated-Temperature Service
The controlled higher-carbon, titanium-stabilized 321 variant used where elevated-temperature strength and creep design govern the specification.
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 | 0.04-0.10 |
|---|---|
| Mn | 2.00 max |
| Si | 0.75 max |
| P | 0.045 max |
| S | 0.030 max |
| Cr | 17.00-19.00 |
| Ni | 9.00-12.00 |
| N | 0.10 max |
| Ti | 4×(C+N) min; 0.70 max |
Properties with context
Minimums, typical indicators and delivered condition
Specified annealed flat-product values
| Room-temperature tensile strength | 515 MPa min |
|---|---|
| Room-temperature 0.2% yield | 205 MPa min |
| Elongation | 40% min |
| Hardness | 95 HRBW max |
Selection indicators
| Density | about 7.9 g/cm3 |
|---|---|
| Producer air-temperature guidance | up to about 850°C / 1560°F; not a design allowable |
| Primary purpose | Stabilized elevated-temperature strength |
| Design basis | Code allowables, creep, time and temperature |
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 321H 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 equipment and case-hardening boxes
Elevated-temperature valves and flanges
Code-approved pressure components
Orders explicitly requiring UNS S32109
Reasons to stop and review
Using room-temperature minimums for creep design
Substituting standard 321 without carbon review
Ignoring wet shutdown corrosion
Ordering without code, form and temperature
Fabrication route
Protect properties through cutting, forming and welding
State the design code, temperature and life.
Qualify filler, heat input and heat treatment.
Check stabilization and grain-size requirements in the governing specification.
Design for thermal expansion and cycling.
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 to ASTM A240/A240M
Tube and pipe under high-temperature product standards
Forgings and fittings under their own specifications
Quarto plate and fabricated furnace 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 321H against the controlling question
Procurement FAQ
Questions to close before placing the order
Is 321H stainless steel magnetic?
Magnetic response depends on microstructure and delivered condition.
Can 321H 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 321H 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 S32109 flat product
Outokumpu Therma 321H/4878 official datasheet
Applicable ASTM high-temperature tube and pipe specifications
Applicable ASME design-code allowable-stress tables