SS 321: properties, composition, uses and standards
SS 321 is a titanium-stabilised austenitic stainless steel, chosen for high-temperature service between 425 and 815 °C. UNS S32100, W.Nr 1.4541, PREN ≈ 18, density 7.92 g/cm³.
What is SS 321?
SS 321 is a titanium-stabilised austenitic stainless steel. Engineers choose it for high-temperature service between 425 and 815 °C. It is also known as AISI 321, UNS S32100, W.Nr 1.4541, Titanium-stabilised stainless.
- UNS
- S32100 · S32109 (321H)
- W.Nr
- 1.4541
- EN
- X6CrNiTi18-10
- JIS
- SUS 321
- BS
- 321S31
- Density
- 7.92 g/cm³
- Melting range
- 1400 – 1425 °C
- Magnetic
- Non-magnetic annealed
- PREN (approx.)
- ≈ 18
Chemical composition and what each element does
| Element | Weight % |
|---|---|
| Chromium | 17.0 – 19.0 |
| Nickel | 9.0 – 12.0 |
| Titanium | 5 × (C + N) min, 0.70 max |
| Carbon | 0.08 max |
| Manganese | 2.00 max |
| Silicon | 0.75 max |
| Nitrogen | 0.10 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.030 max |
| Iron | Balance |
Per ASTM A240 for UNS S32100.
About 18% chromium forms the passive film that makes the steel stainless.
Nickel keeps the structure austenitic — tough at low temperature and easy to form and weld.
Titanium ties up carbon, so 321 keeps its corrosion resistance after long service in the sensitising range.
321H with higher carbon is used above about 540 °C for better creep strength.
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength | 515 MPa · 75 ksi |
| Yield strength 0.2% | 205 MPa · 30 ksi |
| Elongation | 40% |
| Hardness | 217 HB max |
Annealed plate & sheet, minimum values. Values for pipe, bar and forgings differ slightly — see the product standard.
Where SS 321 is used
- Aircraft exhaust. Manifolds, bellows and exhaust systems. Industry →
- Refinery & petrochemical. Heater tubes and piping in the sensitising range. Industry →
- Expansion joints. Bellows for hot lines. Industry →
- Boilers & heat exchangers. Tubes and shells at elevated temperature. Industry →
Welding 321
The matching filler is ER347 (AWS A5.9). ER321 is rare; ER347 is the usual filler.
Keep heat input moderate and interpass temperature low, clean joints thoroughly, and pickle or passivate after welding where the service is corrosive.
SS 321 compared with similar grades
| Grade | PREN | Choose it for |
|---|---|---|
| SS 321 | ≈ 18 | High-temperature service between 425 and 815 °C |
| SS 304 | ≈ 18 | General corrosion resistance, food, water and architectural work |
| SS 347 | ≈ 18 | Welded high-temperature piping in refineries and power plants |
| SS 310 / 310S | ≈ 25 | Furnaces, burners and heat treatment at high temperature |
SS 321 standards by product
Buying SS 321: what to specify
- The product standard and the UNS or designation — for example ASTM A240 UNS S32100.
- Size, thickness or schedule, and quantity in pieces and kg or metres.
- Heat-treatment condition where the standard offers a choice.
- Certificate: EN 10204 3.1 as standard, 3.2 if a third party must witness.