904L Stainless Steel
UNS N08904 · Built for sulphuric acid
904L is a low-carbon, high-alloy austenitic stainless steel with 23–28% nickel, 4–5% molybdenum and a deliberate 1–2% copper addition. The copper is what distinguishes it: it gives resistance to sulphuric and phosphoric acid that ordinary austenitic grades cannot match, while the high nickel and molybdenum provide strong resistance to chloride pitting and stress corrosion cracking.
When to specify 904L
Choose 904L where reducing acids — particularly sulphuric and phosphoric — attack 316, and where chloride stress corrosion cracking must also be controlled. If the duty is chloride resistance alone and higher strength would help, Duplex 2205 is usually more economical. If the medium is more aggressive still, a nickel alloy such as Inconel 625 or Hastelloy is the next step.
Chemical Composition (%)
Composition and mechanical values are the limits set by the governing ASTM specification and are given for reference. The mill test certificate supplied with your consignment carries the actual heat analysis.
| Element | 904L (N08904) |
|---|---|
| Carbon | 0.020 max |
| Chromium | 19.0 – 23.0 |
| Nickel | 23.0 – 28.0 |
| Molybdenum | 4.0 – 5.0 |
| Copper | 1.0 – 2.0 |
| Manganese | 2.00 max |
| Silicon | 1.00 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.035 max |
Mechanical & Physical Properties
| Property | 904L | SS 316L for comparison |
|---|---|---|
| Tensile strength | 490 MPa min | 485 MPa min |
| Yield strength (0.2%) | 220 MPa min | 170 MPa min |
| Elongation in 50 mm | 35% min | 40% min |
| Density | 7.95 g/cm³ | 8.00 g/cm³ |
| PREN (typical) | ≈ 35 | ≈ 25 |
Governing Standards
| Standard | Covers |
|---|---|
| ASTM B677 / B673 | Seamless and welded pipe |
| ASTM B674 | Welded tube |
| ASTM B625 | Plate, sheet and strip |
| ASTM B649 | Bar and wire |
| ASTM A240 (UNS N08904) | Plate, sheet and coil |
| ASTM A182 F904L | Forged fittings and flanges |
Equivalent Designations
| Standard | Designation |
|---|---|
| UNS | N08904 |
| EN / Werkstoff | 1.4539 (X1NiCrMoCu25-20-5) |
| Common name | 904L, Alloy 904L, UNS N08904 |
Typical Applications
- Sulphuric and phosphoric acid plant
- Flue gas desulphurisation and scrubbers
- Pulp and paper bleaching equipment
- Seawater and brine handling
- Pickling lines and acid storage
Industries Served
- Chemical
- Petrochemical
- Power
- Marine
- Pharmaceutical
904L Products We Supply
Available in the forms below, minimum order quantity 5 kg, with a mill test certificate to EN 10204 3.1 traceable to the heat number.
Need 904L in a form not listed above? We source to requirement — and we will confirm availability and lead time.
904L by product form
Governing standards, dimensions and stock availability for each form.
904L — Frequently Asked Questions
- Why does 904L contain copper?
- The 1–2% copper addition is deliberate and is the reason 904L exists. Copper markedly improves resistance to reducing acids, above all sulphuric acid across a wide range of concentrations, where standard austenitic grades corrode. Without the copper, 904L would behave much like a high-nickel version of 317L.
- Is 904L better than Duplex 2205?
- They solve different problems. 904L is better in reducing acids such as sulphuric and phosphoric. Duplex 2205 has roughly twice the yield strength, which often allows a thinner and cheaper section, and is generally more economical where the requirement is chloride resistance rather than acid resistance. Tell us the medium, concentration and temperature and we will advise which fits.
- Is 904L magnetic?
- No. 904L is fully austenitic and remains non-magnetic even after cold work, unlike 304 and 316 which can become weakly magnetic when formed or machined. This matters in instrumentation and in applications where magnetic permeability is specified.
Send your 904L requirement
Tell us the form, size, quantity and standard and our technical team will confirm stock and send a firm price. Minimum order quantity 5 kg, mill test certificates supplied as standard.