304 Stainless vs 321 Stainless
304 and 321 are closely related austenitic 18/8 stainless grades; 321 is essentially 304 stabilized with a titanium addition. That titanium prevents chromium-carbide precipitation during welding and high-temperature service, so engineers weigh them mainly when parts will be welded and then run hot in the 425-870°C band — where unstabilized 304 can sensitize and intergranular corrosion sets in, while 321 stays sound.
The verdict
Choose 304 for general corrosion-resistant parts at ambient or moderate temperatures — it is cheaper, widely stocked and forms easily. Choose 321 when the part is welded and operates in the 425-870°C range, where its titanium stabilization prevents chromium-carbide precipitation (sensitization) and intergranular corrosion that would degrade 304.
Side-by-side data
| Property | 304 Stainless | 321 Stainless |
|---|---|---|
| Category | Stainless Steel | Stainless Steel |
| Density (g/cm³) | 8.0 | 8 |
| Tensile strength (MPa) | 515 | 620 |
| Yield strength (MPa) | 215 | 240 |
| Elongation (%) | 40 | 45 |
| Hardness | 201 HB | 80 HRB |
| Max service temp (°C) | 870 | 870 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 16 | 16 |
| Typically used for | General corrosion-resistant parts | High-temp welded exhaust & ducting |
Which should you choose?
Choose 304 Stainless when…
- The application is general corrosion resistance at ambient or moderate temperature
- Cost and availability matter — 304 is the cheaper, more stocked grade
- The part is deep-formed or drawn (40% elongation forms readily)
- No prolonged exposure in the 425-870°C sensitization range is expected
- A standard, proven all-round stainless is sufficient
- You want easy welding without needing titanium stabilization (for thin sections used cold)
Choose 321 Stainless when…
- The part is welded and then runs hot in the 425-870°C sensitization band
- Applications like exhaust systems, ducting, manifolds and heat exchangers
- Intergranular corrosion after welding must be prevented (titanium ties up carbon)
- Sustained high-temperature creep and oxidation resistance are needed
- You want higher as-supplied tensile strength (620 vs 515 MPa)
- Repeated thermal cycling would sensitize an unstabilized grade like 304
Key differences that matter
- 321 is 304 stabilized with titanium to tie up carbon and prevent chromium-carbide precipitation
- Titanium stabilization makes 321 resistant to sensitization/intergranular corrosion after welding and hot service
- 321 shows higher listed tensile (620 vs 515 MPa); both have ~240 vs 215 MPa yield in this data
- Both are austenitic 18/8, non-magnetic, with similar corrosion resistance at ambient temperature
- Both serve to ~870°C, but 321 holds up better through the 425-870°C sensitization range
- 304 is cheaper and more readily available; 321 commands a premium for the titanium
- Both form and weld well; 321 specifically protects welded, high-temperature joints
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Open the Material SelectorGet a Quote →Frequently asked questions
What is the main difference between 304 and 321?
321 is 304 with a titanium addition that stabilizes it against sensitization. The titanium preferentially combines with carbon, preventing chromium carbides from forming at grain boundaries when the steel is welded or held in the 425-870°C range. That keeps 321 immune to the intergranular corrosion that can attack welded 304 in hot service.
Is 321 better than 304 at high temperature?
For welded parts in the sensitization range, yes. Both grades are rated to roughly 870°C, but 321's titanium stabilization gives it better resistance to intergranular attack and good creep and oxidation behavior during sustained high-temperature service, which is why it is favored for exhaust manifolds and ducting.
Is 304 cheaper than 321?
Yes. 304 is one of the most common, widely-stocked stainless grades and carries a lower relative cost, while 321 pays a premium for its titanium addition and is less commonly stocked. For ambient or moderate-temperature parts that never sensitize, 304 delivers the same corrosion performance for less money.
Which is stronger, 304 or 321?
In this data 321 shows a higher tensile strength (about 620 MPa versus 304's 515 MPa) with comparable yield. Practically, both are soft austenitic grades whose strength advantage is secondary; 321 is specified for its thermal stability rather than raw strength.
Can both grades be welded?
Yes, both weld well. The distinction is what happens afterward in heat: an unstabilized 304 weld held in the sensitization range can develop intergranular corrosion, whereas 321's titanium prevents it. For welded assemblies that will run hot, 321 (or a low-carbon 304L) is the safer specification.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.