SS 304: properties, composition, uses and standards
SS 304 is a austenitic chromium-nickel stainless steel, chosen for general corrosion resistance, food, water and architectural work. UNS S30400, W.Nr 1.4301, PREN ≈ 18, density 8 g/cm³.
What is SS 304?
SS 304 is a austenitic chromium-nickel stainless steel. Engineers choose it for general corrosion resistance, food, water and architectural work. It is also known as AISI 304, UNS S30400, W.Nr 1.4301, 18/8 stainless.
- UNS
- S30400
- W.Nr
- 1.4301
- EN
- X5CrNi18-10
- JIS
- SUS 304
- BS
- 304S31
- Density
- 8 g/cm³
- Melting range
- 1400 – 1450 °C
- Magnetic
- Non-magnetic annealed; slightly magnetic after cold work
- PREN (approx.)
- ≈ 18
Chemical composition and what each element does
| Element | Weight % |
|---|---|
| Chromium | 17.5 – 19.5 |
| Nickel | 8.0 – 10.5 |
| Carbon | 0.07 max |
| Manganese | 2.00 max |
| Silicon | 0.75 max |
| Nitrogen | 0.10 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.030 max |
| Iron | Balance |
Per ASTM A240 for UNS S30400.
About 18% chromium forms the passive film that makes the steel stainless.
Nickel keeps the structure austenitic — tough at low temperature and easy to form and weld.
Up to 0.07% carbon: fine for most work, but choose 304L where heavy sections are welded and service is corrosive.
Without molybdenum, 304 pits in chlorides — step up to 316L for coastal or salty service.
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength | 515 MPa · 75 ksi |
| Yield strength 0.2% | 205 MPa · 30 ksi |
| Elongation | 40% |
| Hardness | 201 HB max |
Annealed plate & sheet, minimum values. Values for pipe, bar and forgings differ slightly — see the product standard.
Where SS 304 is used
- Food & dairy. Tanks, piping and equipment that must be cleaned daily. Industry →
- Water & utilities. Pipework and tanks for potable and process water. Industry →
- Architecture. Cladding, handrails and trim. Industry →
- Chemical processing. Mildly corrosive process lines and vessels. Industry →
- Pharmaceutical. Utility and process equipment. Industry →
- Heat exchangers. Tubes and shells for clean-water duty. Industry →
Welding 304
The matching filler is ER308 / ER308L (AWS A5.9). ER309L for dissimilar joints to carbon steel.
Keep heat input moderate and interpass temperature low, clean joints thoroughly, and pickle or passivate after welding where the service is corrosive.
SS 304 compared with similar grades
| Grade | PREN | Choose it for |
|---|---|---|
| SS 304 | ≈ 18 | General corrosion resistance, food, water and architectural work |
| SS 316 / 316L | ≈ 24 | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 304L | ≈ 18 | Welded tanks, piping and vessels in general corrosive service |
| SS 904L | ≈ 35 | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
SS 304 standards by product
Buying SS 304: what to specify
- The product standard and the UNS or designation — for example ASTM A240 UNS S30400.
- Size, thickness or schedule, and quantity in pieces and kg or metres.
- Heat-treatment condition where the standard offers a choice.
- Certificate: EN 10204 3.1 as standard, 3.2 if a third party must witness.