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.
Quotation brief
Quote 904L When
Quote 904L for process equipment exposed to reducing acids or mixed acid-and-chloride conditions where 316L lacks sufficient general-corrosion or stress-corrosion-cracking margin. Its copper, nickel and molybdenum additions do not create universal acid resistance: concentration, temperature, aeration, contaminants, weld condition and shutdown deposits must be reviewed against current corrosion data before material approval.
Best fit
- Sulfuric- or phosphoric-acid process equipment where the actual concentration and temperature fall within an approved 904L corrosion envelope.
- Flue-gas cleaning, pulp and chemical systems that combine acidic condensate with chloride exposure and require an austenitic fabrication route.
- Components needing high ductility and non-magnetic annealed behavior where duplex fabrication or phase-balance controls are unsuitable.
Limits to check
- 904L is not automatically suitable for every sulfuric-acid concentration, hot chloride brine or stagnant seawater condition; corrosion review remains service-specific.
- High alloy content increases work hardening and affects machining, forming consumables and current quotation, so no fixed cost premium should be assumed.
- UNS N08904, EN 1.4539 and trade descriptions are cross-references only; the ordered product standard and project approval govern substitution.
Quoted product forms
Quoted product forms for 904L Stainless Steel (UNS N08904)
We quote 904L Stainless Steel as sheet / plate, pipe / tube, bar against the named product standard.
- Traceability: heat or lot identity plus the inspection document named in the RFQ (EN 10204 3.1 when that route supports it).
- Processing: decoiling, cutting, polishing, shearing and beveling as ordered.
- Next step: send product form, size and quantity; we quote the supply route.
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 |
Ordering Checks for 904L
- Provide the full process chemistry, concentration range, operating and cleaning temperatures, aeration state, contaminants and expected shutdown conditions.
- State product form, governing material standard, dimensions, finish, edge or end condition and any forming or weld procedure requirements.
- Specify corrosion testing, PMI, supplementary examination and inspection-certificate requirements only where the project or purchase specification requires them.
- Ask the quotation to identify the proposed supply route and confirm that the material certificate reports UNS N08904 chemistry for the ordered product.
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. Send the required product form, dimensions, condition and finish; we quote the matching supply route.
Browse related product hubs:Sheet & plate,Coil & strip,Pipe & tube,Bar & rod.
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
904L Compared With Other Grades
Frequently Asked Questions
What is the difference between 904L and 316L?
904L contains substantially more nickel and molybdenum than 316L and adds copper, improving resistance in selected sulfuric-acid and chloride duties. Its alloy surcharge and production route can materially change the delivered quotation, so compare service requirements, product form and current mill offers rather than assuming a fixed premium.
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.
Published by Tsingshan (Shandong) Iron & Steel Co., Ltd..Sources, update policy and technical limitations.
Quote request
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