304 vs 321 Stainless Steel
Similar Cr-Ni profiles — when titanium stabilization matters and how PMI teams decide.
Key Differences
| Property | 304 | 321 |
|---|---|---|
| ---------- | ----- | ----- |
| Cr | ~18% | ~17–19% |
| Ni | ~8–10% | ~9–12% |
| Ti | — | ≥0.4% (stabilized) |
| Max service temp | ~870°C | ~900°C+ |
| Carbide precipitation | Risk in HAZ | Reduced (Ti stabilized) |
When to use 321
High-temperature exhaust, heat exchangers, and aerospace ducting where welded 304 might sensitize.
XRF Identification
Cr and Ni overlap between 304 and 321 — portable XRF cannot directly measure Ti at low levels in all instruments. Grade ID libraries and application context help distinguish. In PMI, verify heat-service specifications on drawings.