347 vs 321
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
347
Stainless Steel
347 is the niobium-stabilised counterpart of 321, preferred for welded high-temperature service because niobium carbides are more stable during welding thermal cycles. It is a standard grade for aircraft exhausts and refinery equipment.
Standards: DIN 1.4550 · AISI 347 · JIS SUS347 · GB 06Cr18Ni11Nb
321
Stainless Steel
321 is a titanium-stabilised 18-10 stainless developed for welded equipment operating between 425 and 900 °C, where unstabilised 304 would sensitise. It is a long-standing aircraft and exhaust-system grade.
Standards: DIN 1.4541 · AISI 321 · JIS SUS321 · GB 06Cr18Ni11Ti
Chemical composition compared (%)
| Element | 347 | 321 |
|---|---|---|
| C | ≤0.08 | ≤0.08 |
| Si | ≤0.75 | ≤0.75 |
| Mn | ≤2.00 | ≤2.00 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.030 | ≤0.030 |
| Cr | 17.00–19.00 | 17.00–19.00 |
| Ni | 9.00–13.00 | 9.00–12.00 |
| Nb | 10×C–1.00 | — |
| Ti | — | 5×(C+N)–0.70 |
| N | — | ≤0.10 |
Properties compared
| Property | 347 | 321 |
|---|---|---|
| Delivery condition | Annealed | Annealed |
| Hardness | ≤217 HB (annealed) | ≤217 HB (annealed) |
| Tensile strength | 515–690 MPa | 515–690 MPa |
| Density | 7.90 g/cm³ | 7.90 g/cm³ |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: 347 · 321. Substitution decisions for certified parts stay with the design authority.