Grade dossier
321 Stainless Steel for Stabilized Thermal-Cycling Service
A titanium-stabilized 18Cr-9Ni grade used for welded components and intermittent elevated-temperature exposure where resistance to sensitization is important.
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 | 17.00-19.00 |
| Ni | 9.00-12.00 |
| N | 0.10 max |
| Ti | 5×(C+N) min; 0.70 max |
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 7.9 g/cm3 |
|---|---|
| Stabilization | Titanium reduces chromium-carbide sensitization risk |
| Typical producer chemistry | about 17.3Cr-9.1Ni with Ti |
| High-temperature note | Use 321H when the approved design specifically requires it |
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 321 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
Automotive exhaust and thermal-cycling components
Stack liners and annealing covers
Welded pressure vessels under an approved code
Flanges, valves and high-temperature gaskets
Reasons to stop and review
Treating 321 as a substitute for every 304L application
Ignoring chloride corrosion because the grade is stabilized
Using room-temperature properties for creep design
Specifying a mirror finish without surface trials
Fabrication route
Protect properties through cutting, forming and welding
State whether stabilization treatment or post-weld condition is required.
Qualify filler, heat input and inspection for the service.
Review high-temperature design with the applicable code.
Expect titanium-bearing inclusions to affect premium polishing.
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
Bar, tube, pipe and forgings under product-specific standards
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 321 against the controlling question
Procurement FAQ
Questions to close before placing the order
Is 321 stainless steel magnetic?
Magnetic response depends on microstructure and delivered condition.
Can 321 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 321 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 S32100 flat product
Outokumpu Core 321/4541 official grade guidance
Outokumpu Core range official datasheet
Applicable product specification and design code for elevated-temperature service