EN 10253-2 Type B buttweld pipe fittings in 1.4541 — 321 Ti-stabilised austenitic stainless steel (X6CrNiTi18-10, S32100). Titanium is added at minimum 5×C to stabilise carbon as TiC instead of Cr₂₃C₆ — preventing sensitisation during service in the 400–800°C temperature range. Used where components operate continuously at elevated temperature and cannot be solution-annealed after welding.
C ≤0.030% prevents sensitisation in welded service at ambient temperature. But if the component is then exposed to 400–800°C in service (furnace tubes, exhaust ducting, high-temp vessels), residual carbon can still migrate slowly to grain boundaries over time. Not the right choice for continuous high-temperature service.
Titanium (Ti ≥5×C) ties up carbon as stable TiC carbides at all temperatures — chromium cannot form Cr₂₃C₆ because there is no free carbon available. The result is immunity to sensitisation even during extended service at 400–800°C, making 321 the correct choice for components that operate continuously at elevated temperature.
| Element | Min | Max | Note |
|---|---|---|---|
| C (Carbon) | — | 0.080% | Tied up by Ti as TiC |
| Cr (Chromium) | 17.0% | 19.0% | Passive film |
| Ni (Nickel) | 9.0% | 12.0% | Austenite stabiliser |
| Ti (Titanium) | 5×C min | 0.70% | Stabilises C — prevents sensitisation |
| Mo | — | — | None — no Mo in 321 |
| W.Nr. | 1.4541 |
| EN Name | X6CrNiTi18-10 |
| ASTM UNS | S32100 |
| ASTM Grade | A403 WP321 |
| Common Name | 321 |
Filler: ER347 (Nb-stabilised, AWS A5.9). ER321 (Ti filler) is not used because Ti is lost in the arc — Nb-stabilised ER347 provides equivalent weld metal stabilisation. No PWHT required.
