On this page 13 sections
What is SS 321 Stainless Steel?
Quick answer
- Definition
- SS 321 is a titanium-stabilised 18-10 austenitic stainless steel that resists intergranular corrosion after exposure at 425–815 °C, the carbide-precipitation range.
- Family
- Austenitic stainless steel
- Key strength
- Titanium-stabilised: Ti ≥ 5×(C+N)
- Main forms
- Pipes, Tubes, Plates, Sheets, Coils, Bars
- Typical uses
- Exhaust systems and manifolds; Expansion joints and bellows; Refinery and petrochemical heaters
Titanium in SS 321 combines with carbon so chromium carbides don't form at grain boundaries during welding or high-temperature service. That makes SS 321 suitable for parts that operate intermittently or continuously in the sensitising range, such as exhaust manifolds, expansion joints, aircraft exhausts and refinery equipment.
Corrosion resistance at room temperature is similar to SS 304. Its main advantage is stability and strength at elevated temperature. Titanium doesn't transfer well across a welding arc, so SS 347-type (niobium-stabilised) filler is normally used to weld SS 321.
Key characteristics
- Titanium-stabilised: Ti ≥ 5×(C+N)
- Resists sensitisation in the 425–815 °C range
- Higher creep strength than SS 304L
- Welded with SS 347 filler
What are the specifications and equivalents of SS 321?
| Product form | Specification / designation | Product page |
|---|---|---|
| Pipes | ASTM A312 / ASME SA312 TP321 (seamless & welded); A358 EFW | SS 321 pipes → |
| Tubes | ASTM A213 TP321 (seamless); A249 / A269 TP321 (welded) | SS 321 tubes → |
| Plates | ASTM A240 / ASME SA240 321 | SS 321 plates → |
| Sheets | ASTM A240 / ASME SA240 321 | SS 321 sheets → |
| Coils | ASTM A240 / ASME SA240 321 | SS 321 coils → |
| Bars | ASTM A276 / A479 321 | SS 321 bars → |
| Fittings | ASTM A403 WP321 (butt-weld); A182 F321 (forged) | SS 321 fittings → |
| Flanges | ASTM A182 / ASME SA182 F321 | SS 321 flanges → |
| Bolts | ASTM A193 B8T | SS 321 bolts → |
| Nuts | ASTM A194 Grade 8T | SS 321 nuts → |
| Washers | 321 washers | SS 321 washers → |
UNS S32100 · EN 1.4541 (cross-reference; limits are similar but not identical)
Standards: ASTM A312, ASTM A358, ASTM A249, ASTM A269, ASTM A240, ASTM A276, ASTM A182, ASTM A403, ASTM A262, ASTM A479, ASTM A480, EN 10088, EN 10216.
What is the chemical composition of SS 321?
| Element | Limit (%) |
|---|---|
| C | 0.08 max |
| Mn | 2.00 max |
| P | 0.045 max |
| S | 0.030 max |
| Si | 0.75 max |
| Cr | 17.0 – 19.0 |
| Ni | 9.0 – 12.0 |
| Ti | 5×(C+N) – 0.70 |
| N | 0.10 max |
What are the mechanical properties of SS 321?
| Property | Value |
|---|---|
| Tensile strength | 515 MPa (75 ksi) |
| Yield strength (0.2% offset) | 205 MPa (30 ksi) |
| Elongation | 40% |
| Hardness | 217 HBW / 95 HRB |
Physical properties and service temperature
| Property | Value |
|---|---|
| Density (typical) | 7.93 g/cm³ (7930 kg/m³) |
| Magnetism | Essentially non-magnetic when annealed; cold work can make it slightly magnetic. |
| Heat treatment | Solution annealed and rapidly cooled. It can't be hardened by heat treatment, only by cold work. |
| Service temperature | Commonly used for service between about 425 and 815 °C, where unstabilised grades would sensitise. |
How is SS 321 welded and fabricated?
Excellent weldability by TIG, MIG, SMAW and SAW with matching filler. Post-weld heat treatment is not normally needed.
Always follow a qualified welding procedure (for example ASME Section IX) and the filler-metal recommendations for SS 321. Verify incoming material by PMI and check the mill test certificate against the specification.
Which SS 321 products do we supply?
SS 321 Stainless Steel is available in 11 product forms, from ready stock or mill-sourced to your specification, with EN 10204 3.1 mill test certificates (3.2 with third-party inspection on request).
SS 321 SheetsASTM A240 321Specification & sizes
How it's madeHot-rolled coil is cold-rolled to final thickness, then annealed and pickled (2B/2D) or bright annealed (BA), temper-passed, and polished or textured as needed. Coils are then levelled and cut into sheets.
- Specification
- ASTM A240 / ASME SA240 321
- Size range
- Thickness about 0.3 – 6 mm, standard sizes 1,000 × 2,000, 1,219 × 2,438 (4 × 8 ft), 1,250 × 2,500 and 1,500 × 3,000 mm; custom cut lengths
- Finish
- 2B, 2D, BA, No.4 (brushed), HL (hairline), No.8 (mirror), embossed, PVC or laser-film protected
- Ends
- Sheared or slit edges; laser-cut blanks on request
Testing & documents
- Chemical and mechanical tests
- Surface and finish inspection
- Thickness and flatness checks
- Hardness and bend tests as specified
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 321 CoilsASTM A240 321Specification & sizes
How it's madeHot-rolled coil (HRC) comes from the hot-strip mill. Cold-rolled coil (CRC) is further reduced on a cold mill, then annealed and pickled or bright annealed, and skin-passed. Slitting lines cut master coils into narrow strips to the width you order.
- Specification
- ASTM A240 / ASME SA240 321
- Size range
- Thickness about 0.3 – 12 mm; widths from narrow slit strip (about 10 mm) to 1,250 / 1,500 / 2,000 mm; coil ID 508 / 610 mm; coil weights to order
- Finish
- No.1 (hot-rolled, annealed, pickled), 2B, 2D, BA, No.4 for stainless; HR black, pickled & oiled, CR for carbon steel
- Ends
- Mill edge or slit edge
Testing & documents
- Chemical and mechanical tests
- Thickness profile and surface inspection
- Hardness and bend tests
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 321 BoltsASTM A193 B8TSpecification & sizes
How it's madeCut from heat-treated bar (or forged and heat treated), then threaded by rolling or cutting, and coated if required.
- Specification
- ASTM A193 B8T
- Size range
- M6 – M100 and ¼" – 4" (larger on request); lengths to flange tables or drawing
- Finish
- Plain, black oxide, zinc, hot-dip galvanised, PTFE-based fluoropolymer, zinc-nickel
- Ends
- Chamfered points; full or partial thread
Testing & documents
- Chemical and mechanical tests of bar and finished bolts
- Hardness tests
- Proof-load and wedge tests where applicable
- Coating thickness and adhesion
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 321 NutsASTM A194 Grade 8TSpecification & sizes
How it's madeHot-forged or cold-formed from bar, heat treated (for hardenable grades), tapped and coated if required.
- Specification
- ASTM A194 Grade 8T
- Size range
- M6 – M100 and ¼" – 4"; heavy hex to ASME B18.2.2; metric to ISO 4032 / 4033
- Finish
- Plain, zinc, galvanised (tapped oversize), fluoropolymer
Testing & documents
- Proof-load tests
- Hardness tests
- Chemical analysis
- EN 10204 3.1 certificate; 3.2 with third-party inspection
SS 321 WashersSS 321 washersSpecification & sizes
How it's madeStamped or machined from plate or strip and heat treated where required.
- Specification
- SS 321 washers
- Size range
- M6 – M100 and ¼" – 4" bolt sizes
- Finish
- Plain, zinc, galvanised
Testing & documents
- Hardness tests
- Dimensional checks
- EN 10204 3.1 certificate; 3.2 with third-party inspection
Where is SS 321 used?
Typical applications
- Exhaust systems and manifolds
- Expansion joints and bellows
- Refinery and petrochemical heaters
- Aircraft exhaust and firewalls
- Boiler casings and high-temperature chemical equipment
Where do we supply SS 321?
SS 321 is regularly requested for projects in these markets:
What should you specify when buying SS 321?
- Grade and specification, e.g. ASTM A312 TP321
- Product form, size and tolerance
- Heat treatment / condition and surface finish
- Quantity, delivery location and required date
- Tests: PMI, hydro/NDT, IGC, impact or hardness as required
- Certificate type (EN 10204 3.1 / 3.2) and third-party inspection
See our RFQ checklist guide and what drives metal prices.
Explore more on SS 321
SS 321 products
Guides
Comparisons & articles
Related grades
Frequently asked questions
Why is titanium added to SS 321?
Titanium forms stable carbides, which stops chromium carbide precipitation at grain boundaries during welding and high-temperature service, and so prevents intergranular corrosion.
What filler is used to weld SS 321?
Usually SS 347-type (niobium-stabilised) filler, such as ER347, because titanium is largely lost across the arc.
What is SS 321 used for?
Exhaust systems and manifolds, Expansion joints and bellows, Refinery and petrochemical heaters, Aircraft exhaust and firewalls. It's used across Petrochemical & Refining, Power Generation, Aerospace, Oil & Gas.
What is the UNS number of SS 321?
SS 321 is designated UNS S32100; the closest EN cross-reference is 1.4541.
Which product forms is SS 321 available in?
Pipes, Tubes, Plates, Sheets, Coils, Bars, Fittings, Flanges, Bolts, Nuts, Washers, to ASTM A312 TP321, ASTM A213 TP321, ASTM A240 321 and related specifications.
What is the density of SS 321?
About 7.93 g/cm³ (7930 kg/m³), used for weight calculations.
Is SS 321 magnetic?
Essentially non-magnetic when annealed; cold work can make it slightly magnetic.
What temperature can SS 321 withstand?
Commonly used for service between about 425 and 815 °C, where unstabilised grades would sensitise.