SS 321 vs SS 304 difference in composition & properties.
SS 321 and SS 304 have closely matching chemistry.
321 or 304 for high temperature?
SS 321 is 304 stabilised with titanium. The titanium ties up carbon, so 321 resists intergranular corrosion after long service at about 425–815 °C, for example in exhaust systems, expansion bellows and heat exchangers. For ordinary temperatures, 304 or 304L is the economical choice.
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Key differences between SS 321 and SS 304
The chemistry limits are close; compare the table below line by line.
SS 321 vs SS 304 chemical composition (weight %)
| Element | SS 321 | SS 304 |
|---|---|---|
| C | ≤0.08 | ≤0.07 |
| Si | ≤0.75 | ≤0.75 |
| Mn | ≤2 | ≤2 |
| P | ≤0.045 | ≤0.045 |
| S | ≤0.03 | ≤0.03 |
| Cr | 17–19 | 17.5–19.5 |
| Ni | 9–12 | 8–10.5 |
| N | ≤0.1 | ≤0.1 |
| Ti | ≤0.7 | – |
Mechanical properties, equivalents and uses
| Property | SS 321 | SS 304 |
|---|---|---|
| Family | Austenitic stainless | Austenitic stainless |
| Tensile strength, MPa | ≥515 | ≥515 |
| Yield strength, MPa | ≥205 | ≥205 |
| Elongation, % | ≥40 | ≥40 |
| Hardness | ≤217 HB | ≤201 HB |
| Density, g/cm³ | 7.92 | 7.93 |
| UNS | S32100 | S30400 |
| EN | X6CrNiTi18-10 | X5CrNi18-10 |
| W.Nr | 1.4541 | 1.4301 |
| JIS | SUS321 | SUS304 |
| IS (India) | X04Cr18Ni10Ti (IS 6911) | X04Cr18Ni10 (IS 6911) |
| AISI / ASTM | AISI 321 | AISI 304 |
| Typical uses | Exhausts, bellows, hot refinery lines | Food, dairy, kitchen, water, architecture, general process |
Mechanical values: Annealed plate, sheet, strip (ASTM A240 / ASME SA240). Limits vary by standard and product form; confirm against your purchase specification.
Frequently asked questions
What is the difference between SS 321 and SS 304?
SS 321 and SS 304 have similar chemistry; check the full table for the limits that differ.
Where are SS 321 and SS 304 used?
SS 321: Exhausts, bellows, hot refinery lines. SS 304: Food, dairy, kitchen, water, architecture, general process.
Can SS 304 replace SS 321?
Only if the purchase specification allows it. Check the governing standard, chemistry limits and mechanical properties against the order, and confirm on the mill test certificate.
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Mill test certificate (EN 10204 3.1) supplied with material; third-party inspection on request.
Reference basis: Compiled by Steel Impex India. Check each table’s source, product form and delivery condition before use. Sources, calculation methods and corrections.