904L Stainless Steel (UNS N08904)
Super-austenitic · ASTM A240/A240M, B625 · Density 8 g/cm³
904L (UNS N08904) is a super-austenitic stainless steel with about 25% nickel, 20% chromium, 4.5% molybdenum and added copper. Designed for sulfuric and phosphoric acid service, it resists chloride pitting and stress-corrosion cracking far beyond 316L, and is famously used for premium watch cases as well as chemical plant.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | Mo | Cu | P | S |
|---|---|---|---|---|---|---|---|---|
| ≤0.020 | ≤2.00 | ≤1.00 | 19.0–23.0 | 23.0–28.0 | 4.0–5.0 | 1.0–2.0 | ≤0.045 | ≤0.035 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M, B625.
Mechanical Properties
| Tensile strength | ≥490 MPa (71 ksi) |
|---|---|
| Yield strength (0.2%) | ≥215 MPa (31 ksi) |
| Elongation (50 mm) | ≥35% |
| PREN | ≈35 |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M, B625 unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 8 g/cm³ |
|---|---|
| Magnetic response | Essentially non-magnetic after solution annealing; cold work can introduce a measurable magnetic response. |
| Microstructure | Super-austenitic |
Corrosion Resistance & Limits
- 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 & Heat Treatment
| Welding | 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. |
| Machining | 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. |
Equivalent Grades
The closest international equivalents of 904L Stainless Steel are 1.4539 (X1NiCrMoCu25-20-5) in the EN system, SUS890L in the JIS system, 015Cr21Ni26Mo5Cu2 in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | N08904 |
| EN | 1.4539 (X1NiCrMoCu25-20-5) |
| JIS | SUS890L |
| GB | 015Cr21Ni26Mo5Cu2 |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 904l stainless steel: Sheet / Plate, Pipe / Tube, Bar.
| Finishes | No.1, 2B |
|---|---|
| Sheet / coil thickness | 0.5–6.0 mm |
| Plate thickness | 6–40 mm |
Common surface and delivery options: No.1, 2B, BA or mechanically polished finish when supported by the product route; Annealed and pickled, descaled or polished tube finish as specified; Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Sulfuric and phosphoric acid equipment
- Flue-gas desulfurization scrubbers
- Seawater cooling and brine systems
- Pulp and paper bleach plants
- Premium watch cases and jewelry
Frequently Asked Questions
What is the difference between 904L and 316L?
904L roughly doubles the nickel and molybdenum of 316L and adds copper. That lifts its pitting resistance (PREN ≈35 vs ≈25) and gives real resistance to hot sulfuric acid and chloride stress-corrosion cracking. The cost is significant — 904L typically prices several times higher than 316L — so it is specified only where 316L demonstrably fails.
Why do luxury watchmakers use 904L?
Its high alloy content takes a finer, brighter polish and resists sweat, chlorinated water and everyday corrosion better than 316L. The mechanical properties are similar; the appeal is surface quality and corrosion margin, not strength.
Is 904L resistant to seawater?
904L handles cool, flowing seawater and brines well, but in warm stagnant seawater with crevices, super-duplex (2507) or 6%-Mo austenitics are safer. As a rule of thumb 904L is chosen for acids; duplex families for hot chloride brines.
904L Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347409L4204394414442507303317L254 SMO440C17-4 PH2304
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