321 · UNS S32100 · W. Nr. 1.4541 · 347 · UNS S34700 · W. Nr. 1.4550 · 06Cr18Ni11Ti / 06Cr18Ni11Nb
Stainless Steel 321 / 347 (S32100 / S34700): composition, properties, fittings and flanges
Types 321 and 347 are stabilised austenitic stainless steels based on the 18 % chromium, 9-12 % nickel composition. Type 321 is stabilised with titanium (minimum 5 times the carbon content) and Type 347 with niobium plus tantalum (minimum 10 times the carbon content). The stabilising elements combine with carbon in preference…
- UNS
- S32100 / S34700
- W. Nr.
- 1.4541 / 1.4550
- Density
- 8.03 g/cm³ (0.290 lb/in³)
- Key strength
- 515 MPa / 75 ksi
Identification and standards
| Short form | 321 · UNS S32100 · W. Nr. 1.4541 · 347 · UNS S34700 · W. Nr. 1.4550 · 06Cr18Ni11Ti / 06Cr18Ni11Nb |
|---|---|
| Classification | Titanium or niobium stabilised austenitic stainless steel |
| UNS | S32100 / S34700 |
| Werkstoff number | 1.4541 / 1.4550 |
| Material family | Stainless Steel |
Chemical composition
| Element | Composition (wt %) | Why it is there |
|---|---|---|
| Chromium (Cr) | 17.0 - 19.0 | Passive film, oxidation resistance |
| Nickel (Ni) | 9.0 - 12.0 | Austenite stability, toughness |
| Titanium (Ti), Type 321 | 5 x (C+N) minimum, 0.70 max | Stabiliser |
| Niobium + Tantalum (Nb+Ta), Type 347 | 10 x C minimum, 1.00 max | Stabiliser |
| Manganese (Mn) | 2.00 max | - |
| Silicon (Si) | 0.75 max | - |
| Phosphorus (P) | 0.045 max | - |
| Sulphur (S) | 0.030 max | - |
| Carbon (C) | 0.08 max | - |
| Iron (Fe) | Balance | Matrix |
Note Single figures are maximum limits unless shown as a range. Always confirm against the heat-specific EN 10204 3.1 certificate supplied with your order.
Mechanical properties
| Tensile strength, min | 515 MPa / 75 ksi |
|---|---|
| 0.2 % yield strength, min | 205 MPa / 30 ksi |
| Elongation in 2 in, min | 40 % |
| Typical hardness, annealed | 150 - 200 HB |
| Typical allowable stress advantage over 304 at 600 °C | Higher for both grades, with 347 typically best |
| Recommended service range in air | To 815 °C for 321, 870 °C intermittent |
Warning Values depend on product form, section thickness and heat treatment. Larger sections generally achieve lower strength than thin product; always design against the applicable code allowable stress rather than these figures.
Physical properties
| Density | 8.03 g/cm³ (0.290 lb/in³) |
|---|---|
| Melting range | 1398 - 1446 °C (2550 - 2635 °F) |
| Modulus of elasticity | 193 GPa (28 x 10⁶ psi) |
| Thermal conductivity at 20 °C | 16.1 W/m·K |
| Mean coefficient of thermal expansion, 20-100 °C | 16.6 µm/m·°C |
| Electrical resistivity at 20 °C | 0.72 µΩ·m |
Specifications by product form
| Pipe, seamless / welded | ASTM A312 / A358 / ASME SA-312 |
|---|---|
| Tube | ASTM A213 (boiler and heat exchanger), A269, A249 |
| Plate / sheet / strip | ASTM A240 / ASME SA-240 |
| Bar / rod / shapes | ASTM A276 / A479 / ASME SA-479 |
| Forgings & flanges | ASTM A182 Grade F321 / F347 / ASME SA-182 |
| Butt weld fittings | ASTM A403 / ASME SA-403 (WP321 / WP347) |
| Welding consumables | ER347 for Type 347, ER321 for Type 321, or ER347 for most dissimilar stabilised joints |
| UNS / EN / China | UNS S32100 / S34700 · W. Nr. 1.4541 / 1.4550 · GB 06Cr18Ni11Ti / 06Cr18Ni11Nb |
Product forms available
Hangbo supplies this grade in the following forms. Sizes outside the listed range can often be produced to order.
- Seamless and welded pipe and boiler tube
- Butt weld elbows, tees and reducers to ASME B16.9
- Forged flanges to ASME B16.5 Class 150-2500
- Bellows and flexible hose components
Typical applications
- Refinery heater tubes, radiant coils and process furnace piping
- Expansion joints, bellows and flexible connectors above 500 °C
- Heavy wall welded pressure vessels that cannot be solution annealed
- Aircraft and rocket exhaust manifolds, collector rings and afterburner parts
- High-temperature bolts, hangers, supports and refractory anchors
- Annealing covers, recuperators, thermal oxidisers and kiln hardware
- Nuclear and power plant piping in the sensitising range
Welding, forming and machining
- Welding
- Use stabilised filler - ER347 is common even when welding 321 - because titanium can be lost from the 321 weld pool in high heat input processes. For maximum weld metal ductility some specifications restrict the niobium plus tantalum ratio in 347 filler.
- Heat treatment
- Standard anneal at 950-1065 °C with rapid cooling. Because both grades resist sensitisation they can be stress relieved at 815-870 °C, and a stabilising treatment at 815-870 °C before final stress relief improves long-term life.
- Machining
- Similar to 304 but titanium carbides in 321 increase tool wear; use sharp carbide tooling, positive rake and ample coolant.
- Service note
- Both grades resist polythionic acid cracking better than unstabilised grades, which is why refineries specify them for hydrocracker and hydrotreater furnace circuits.
Buy Stainless Steel 321 / 347 from Hangbo
Material is supplied with full heat-number traceability, solution annealing or ageing performed under calibrated furnace control, and an EN 10204 3.1 certificate covering chemical analysis, mechanical properties, heat treatment records and the agreed NDT scope. Positive material identification and third party inspection and test reports from SGS are available for critical service.