304 stainless steel properties
An 18 % chromium, 8 % nickel austenitic stainless. It resists corrosion in most atmospheric and food-contact service, forms and welds well, and is non-magnetic as delivered.
- TypeAustenitic 18Cr-8Ni stainless, not hardenable by heat treatment
- StandardsJIS G4303 SUS304 · ASTM A276 / A479 UNS S30400 · EN 1.4301 · GB 06Cr19Ni10
- Density8.0 g/cm³, three times the weight of the same part in aluminium
- Tensile515 MPa minimum annealed to ASTM A276; typically 600 MPa and up after machining
- Yield205 MPa minimum annealed
- Hardness201 HB maximum annealed. The machined surface ends up far harder than the bar
- MagneticNon-magnetic annealed. Machining and cold work make it slightly magnetic, which is normal and not a grade error
- CorrosionGood in atmosphere, water and food service. Pits in chlorides and seawater
- WeldingWeldable. For welded assemblies specify 304L to avoid carbide precipitation at the joint
- CertificateMill test certificate to EN 10204 3.1 on request
A magnet won't tell you the grade. We regularly see 304 parts rejected because a magnet sticks lightly to a machined face. Cold work turns some of the austenite at the surface into martensite, and the material is still 304. If there is doubt, the mill certificate answers it.
304 compared with related grades
| Grade | JIS (Japan) | US (ASTM / AISI / UNS) | GB/T (China) | EN / DIN (Europe) | Cross-reference |
|---|---|---|---|---|---|
| SUS 304 the default | SUS304 (JIS G4303 / G4305) | 304 · UNS S30400 · ASTM A276 / A479 | 06Cr19Ni10 (old 0Cr18Ni9) | X5CrNi18-10 · EN 1.4301 | Standard equivalent |
| SUS 304L low carbon, for welding | SUS304L | 304L · UNS S30403 | 022Cr19Ni10 | X2CrNi19-11 · EN 1.4306 / 1.4307 | Standard equivalent |
| SUS 303 free machining | SUS303 | 303 · UNS S30300 · ASTM A582 | Y12Cr18Ni9 | X8CrNiS18-9 · EN 1.4305 | Standard equivalent |
| SUS 316L chloride service | SUS316L | 316L · UNS S31603 | 022Cr17Ni12Mo2 | X2CrNiMo17-12-2 · EN 1.4404 | Standard equivalent |
Designations taken from JIS G4303 and G4305, ASTM A276, A479 and A582, GB/T 20878 and EN 10088-3. The austenitic grades map cleanly from one system to another. The one thing to watch is 303, where the added sulphur changes how the part corrodes and welds whatever standard it's bought to. Last reviewed 13 September 2026.
304, 304L or 303
Use 304 for general corrosion service
Brackets, housings, shafts, food and beverage equipment parts, fittings, fasteners and anything that lives indoors or in normal weather. It's the cheapest stainless you can find in Vietnamese stock in most sizes.
Use 304L when the part is welded
The lower carbon in 304L stops chromium carbide forming at grain boundaries in the heat-affected zone. That carbide is why a welded 304 joint rusts in a line beside the weld. If your assembly is welded and the drawing says 304, we'll raise 304L as a question before quoting.
Use 303 only where corrosion is not the point
303 has sulphur added to break chips. It machines much faster and costs less to cut, which matters on high-volume turned parts. You give up a measurable amount of corrosion resistance, and it does not weld properly, so it's not an upgrade path from 304.
Move to 316L for chlorides
Seawater, coastal installations, swimming pool hardware, chemical and pharmaceutical contact, de-icing salt. 304 pits in chloride environments and the failure looks like rust spots that no amount of polishing removes.
Not for a hardened wear surface
304 cannot be hardened by heat treatment. If the drawing calls for a hardness in HRC, the material is wrong. The part belongs in 17-4PH, 420 or a hardened tool steel, and it's better to settle that before the PO.
Expect it to cost more to cut than steel
Do not expect a 304 part to price like the same part in carbon steel. Cycle times run longer, tools wear out sooner and the finishing passes are slower.
Machining process
Every failure mode in 304 has the same cause: the tool stopped cutting and started rubbing. Constant feed and a rigid setup matter more than which insert you pick.
- TurningMori Seiki and Okuma lathes to Ø 310 × 800 mm, including twin-spindle, at ±0.005 mm typical
- MillingDoosan, Haas, Hision and FANUC RoboDrill machining centres, 3, 4 and 5-axis
- Feed ruleNo dwelling, and no spring passes with a worn edge. A rubbing tool glazes the surface, and then the next pass has to cut through work-hardened skin
- ToolingSharp positive-rake carbide with a stainless-specific coating. We check edge condition far more often than on aluminium
- DepthDepth of cut set to get under the hardened layer left by the previous pass, not skim along the top of it
- CoolantFlood coolant at proper concentration and pressure, through-spindle where the tool allows. Heat is what kills the edge
- ThreadsCut and rolled, metric and inch. Stainless galls against stainless, so specify anti-seize or a dissimilar fastener at assembly
- InspectionMitutoyo CRYSTA-APEX V CMM in a climate-controlled lab, reported in inch and millimetre
These are figures we hold day to day on this grade. They're not a blanket specification. General tolerance follows ISO 2768 fine or medium class as your print calls it. Stainless gets difficult in deep bores and in long, slender turned parts, so send the drawing and we'll confirm what we can hold before you commit to a PO.
Compatible finishing processes
- PassivationPassivation to the ASTM A967 class your drawing names, checked before shipping
- BlastingGlass or ceramic bead blast for a uniform matte. We never bead blast stainless with media that has been used on carbon steel
- PolishingMechanical polishing to a specified Ra where the drawing calls for it
- ElectropolishElectropolishing where a cleanroom or hygienic finish is specified
- MarkingLaser marking for part number, revision and lot
- Not forAnodising. It's an aluminium process and stainless won't take it
Free iron is what makes stainless rust. Particles picked up from carbon steel tooling, fixtures or blast media leave surface rust that looks like a material fault. For that reason we keep stainless work away from carbon steel work in the shop. Where your drawing calls for passivation, we record the class that was run. Full finishing list →
Stock and lead time
- BarRound and flat bar in 304 and 304L, easy to get from Vietnamese stockists
- PlateCommon thicknesses available; oversized and thick plate confirmed per job
- 303Available in bar for turned parts where corrosion is not critical
- QuoteWithin 24 business hours of a complete RFQ
- Lead timePrototype 3–7 days · small batch 7–14 days · standard 14 days after PO
- CertificateEN 10204 3.1 mill certificate on request, with a dimensional report in inch and millimetre
We confirm stock and section size when we quote. If your drawing calls for 304 and only 304L is available in the size you need, we don't substitute without your written approval, even for an adjacent grade.
Common questions
Is SUS 304 the same as 304?
Yes. SUS is the JIS prefix for stainless steel. SUS304 to JIS G4303 is the same alloy as UNS S30400 to ASTM A276 and EN 1.4301, and the three systems cross-reference cleanly.
Why is my machined 304 part slightly magnetic?
Cold work from machining turns a little of the austenite at the surface into martensite, which is magnetic. That's normal and does not mean you got the wrong grade. Check the mill certificate if you need to be sure.
Should I specify 304 or 304L?
304L if the part is welded, 304 otherwise. The low carbon in 304L prevents the chromium carbide precipitation that makes a welded 304 joint corrode next to the weld.
Can 304 be hardened?
Not by heat treatment. It only hardens by cold work. If your drawing calls out a hardness in HRC, the specified material is probably wrong and we'll ask before quoting.
Will 304 rust?
In chlorides, yes. Coastal air, seawater, pool chemicals and de-icing salt all pit it. It will also show surface rust if free iron from carbon steel tooling is left on it, and passivation removes that. For real chloride service the grade should be 316L.
Can you passivate the parts?
Yes. Passivation is to the ASTM A967 class your drawing specifies, and we record which class was run.
Can you machine 303 instead to bring the price down?
We can quote it as an option for your written approval. 303 machines faster and costs less. In exchange it's less corrosion resistant and does not weld properly, so it's an engineering change.
Related information
316L stainless steel
The chloride-resistant grade. Where the molybdenum is worth paying for, and where 304 stops being enough.
17-4PH stainless steel
Stainless that reaches 40 HRC, where the ageing condition is part of the specification.
Finishing and heat treatment
Passivation, electropolishing, plating and the heat treatment conditions we specify and check.