304 vs 321 Stainless Steel
Side-by-side comparison · Composition · Properties · Selection guide
304 and 321 share an 18Cr-8Ni austenitic base, but 321 adds titanium stabilization to protect welded or heated material from intergranular corrosion. At ordinary service temperatures 304 is cheaper and more available; 321 earns its place in cyclic or sustained elevated-temperature equipment.
Full datasheets:304 Stainless Steel·321 Stainless Steel
At a Glance
| 304 | 321 | |
|---|---|---|
| Type | Austenitic | Austenitic (Ti-stabilized) |
| UNS | S30400 | S32100 |
| Standard | ASTM A240/A240M | ASTM A240/A240M |
| Density | 7.93 g/cm³ | 7.92 g/cm³ |
Corrosion Resistance and Service Limits
304
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
321
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
Fabrication and Heat Treatment
| Operation | 304 | 321 |
|---|---|---|
| Welding | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. |
| Forming | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. |
| Machining | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. |
| Heat treatment | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. |
Chemical Composition (wt%)
| Element | 304 | 321 |
|---|---|---|
| C | ≤0.08 | ≤0.08 |
| Mn | ≤2.00 | ≤2.00 |
| Si | ≤0.75 | ≤0.75 |
| Cr | 17.5–19.5 | 17.0–19.0 |
| Ni | 8.0–10.5 | 9.0–12.0 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.030 | ≤0.030 |
| N | ≤0.10 | — |
| Ti | — | 5×(C+N) min, ≤0.70 |
Mechanical Properties
| Property | 304 | 321 |
|---|---|---|
| Tensile strength | ≥515 MPa (75 ksi) | ≥515 MPa (75 ksi) |
| Yield strength (0.2%) | ≥205 MPa (30 ksi) | ≥205 MPa (30 ksi) |
| Elongation (50 mm) | ≥40% | ≥40% |
| Hardness | ≤201 HBW | — |
| Max intermittent service | — | ≈870 °C |
Which One Should You Choose?
Choose 304 for:
- General sheet, tank and equipment fabrication
- Food, architectural and ambient-temperature service
- Projects needing broad form and finish availability
- Welded work where 304L satisfies sensitization controls
Choose 321 for:
- Exhaust, expansion joint and hot-process components
- Service with repeated exposure in the sensitization range
- Parts requiring elevated-temperature stability
- Specifications that explicitly call for titanium stabilization
Our verdict
304 remains the default for ambient-temperature corrosion and general fabrication; use low-carbon 304L for routine welded work. Select 321 only when elevated-temperature exposure makes stabilization relevant or the governing equipment specification requires it. Titanium does not make 321 a universal corrosion upgrade.
Cost and Availability
Compare the current stock position, mill route, minimum production quantity, processing yield, testing and delivered cost for 304 and 321 at quotation time. A fixed price ratio would be misleading because product form, size, condition and market timing can change the commercial result.
Do Not Substitute Without Review
Do not replace 304 with 321, or the reverse, from the grade name alone. Recheck chemistry, mechanical-property condition, product standard, dimensions, corrosion environment, welding procedure and project approval before substitution.
304 & 321 Products We Export
304 Stainless Steel Sheet
304/304L stainless steel sheet in 2B, BA, No.4 and mirror finish, in quotation-confirmed dimensions, cut to size, with ordered documentation.
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304 Stainless Steel Welded Pipe
304 welded stainless steel pipe and tube to ASTM A312, A249 and A554 — industrial, sanitary and polished decorative, round, square and rectangular sections.
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304 Stainless Steel Round Bar
304/304L stainless steel round bar, in quotation-confirmed dimensions, bright drawn h9/h11 or peeled, cut to length — machining stock with full heat traceability.
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Frequently Asked Questions
Is 321 more corrosion resistant than 304?
In ordinary wet service they are similar. 321 primarily improves resistance to sensitization during elevated-temperature exposure, not chloride pitting resistance.
Can 304L replace 321?
Sometimes for welded ambient service, but not automatically at sustained high temperature where stabilized 321 may be required by design rules or service history.
Can 321 be polished like 304?
Yes, though finish availability is narrower and titanium-related surface features can matter in critical decorative work. Approve a sample if appearance is the main requirement.
RFQ
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Technical content updated: 2026-07-29
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.