SS 904L FastenersASTM A479 UNS N08904 · Manufacturer, stockist & exporter, India
Also sold as Alloy 904L · UNS N08904 · W.Nr 1.4539 · 2RK65
SS 904L fasteners — stud bolts, hex bolts, nuts and washers — are made from ASTM A479 bar stock to ASME B18 dimensions. It is a super-austenitic stainless steel with high nickel, molybdenum and copper, chosen for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. Kanak Steel & Engineering Co. supplies it with EN 10204 3.1 mill certificates from Mumbai to buyers across India, the Gulf, South-East Asia, South America, Europe, the UK and the USA.
- Stock & mill supply
- EN 10204 3.1 / 3.2
- PMI on every heat
- Export packing
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is SS 904L Fasteners?
SS 904L fasteners is a super-austenitic stainless steel with high nickel, molybdenum and copper supplied as fasteners to ASTM A479 (UNS N08904). Buyers specify it for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. It is also sold as Alloy 904L, UNS N08904, W.Nr 1.4539.
- What it is
- Super-austenitic stainless steel with high nickel, molybdenum and copper
- Bar stock
- ASTM A479
- Dimensions
- ASME B18.2.1 · B18.2.2 · B18.31.2
- Threads
- UNC · UN-8 · metric
- Sizes
- M10 – M64 · ½" – 4"
- Best at
- Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water
SS 904L Fasteners Specification & Sizes
| Material | ASTM A479 |
|---|---|
| Dimensional standards | ASME B18.2.1 (bolts) · B18.2.2 (nuts) · B18.31.2 (studs) · DIN 931 / 933 / 934 |
| Types | Stud bolt · Hex bolt · Heavy hex nut · Hex nut · Washer · Threaded rod · U-bolt · Eye bolt · Anchor bolt · Foundation bolt · Socket head cap screw · Machine screw |
| Threads | UNC, UN-8 and metric coarse |
| Coating | Plain · PTFE on request |
| Documents | EN 10204 3.1 |
SS 904L Stud Bolts: Grade & Nut Pairing
SS 904L studs and nuts are machined from ASTM A479 bar; the nut is usually the same alloy. A193 B8-series bolting comes in Class 1 (carbide solution treated) and Class 2 (strain hardened, higher strength) — state the class.
Torque (T = K × F × d), stud length and coatings are covered in the fasteners guide.
| Galling | Stainless and nickel-alloy threads gall — always use anti-seize, and avoid high-speed tightening |
|---|---|
| Coatings | Usually supplied plain; PTFE coating on request to ease tightening |
| Marking | Grade symbol and maker's mark on each stud end and nut, as the standard requires |
| Certificates | EN 10204 3.1 for the bar heat; mechanical test reports on the finished bolts on request |
SS 904L Fasteners Chemical Composition
| Element | Weight % |
|---|---|
| Nickel | 23.0 – 28.0 |
| Chromium | 19.0 – 23.0 |
| Molybdenum | 4.0 – 5.0 |
| Copper | 1.0 – 2.0 |
| Carbon | 0.020 max |
| Manganese | 2.00 max |
| Silicon | 1.00 max |
| Nitrogen | 0.10 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.035 max |
| Iron | Balance |
SS 904L Fasteners Mechanical Properties
| Annealed plate & sheet | Value |
|---|---|
| Tensile strength | 490 MPa · 71 ksi |
| Yield strength 0.2% | 220 MPa · 31 ksi |
| Elongation | 35% |
| Hardness | 90 HRB max |
Density & Physical Properties
| Property | Value |
|---|---|
| Density | 7.95 g/cm³ |
| Melting range | 1300 – 1390 °C |
| Magnetic | Non-magnetic (annealed) |
| PREN (approx.) | ≈ 35 |
SS 904L Equivalent Grades
Values follow ASTM A240 for UNS N08904. Always check against the edition named on your purchase order.
Six-digit Harmonized System heading (iron and steel, chapter 72–73). Your country adds its own digits — confirm with your customs broker. All HS codes.
How to Verify SS 904L Fasteners with PMI
Positive material identification with a handheld XRF gun confirms the alloy on the piece itself, in seconds, before it is cut or welded. SS 904L is most often mixed up with Inconel 825 — the table shows which elements tell them apart.
Handheld XRF does not measure carbon or nitrogen; those come from the mill certificate or optical emission (OES) testing. We PMI-test nickel alloys as standard and any grade on request.
| Element | SS 904L | Inconel 825 |
|---|---|---|
| Nickel | 23.0 – 28.0 | 38.0 – 46.0 |
| Chromium | 19.0 – 23.0 | 19.5 – 23.5 |
| Molybdenum | 4.0 – 5.0 | 2.5 – 3.5 |
| Copper | 1.0 – 2.0 | 1.5 – 3.0 |
| Titanium | residual | 0.6 – 1.2 |
| Iron | Balance | 22.0 min |
| Manganese | 2.00 max | 1.0 max |
SS 904L fasteners by type
SS 904L Fasteners Applications
SS 904L is specified when the cheaper grade will not survive the service but a higher alloy would be more than the job needs. These are the jobs our buyers use it for.
SS 904L Fasteners vs 316L, 2205 and 825
| Grade | Fasteners standard | PREN (approx.) | Pick it when |
|---|---|---|---|
| SS 316 / 316L | ASTM A193 B8M · A194 8M | ≈ 24 | Chloride-bearing process fluids, marine air and pharmaceutical service |
| Inconel 825 | ASTM B425 | ≈ 31 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| Duplex 2205 | ASTM A276 / A479 | ≈ 35 | Strength with chloride resistance at a stainless-steel budget |
| SS 904L | ASTM A479 | ≈ 35 | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
PREN = Cr + 3.3 Mo + 16 N, from mid-range chemistry. A screening guide, not a substitute for corrosion data on your medium.
SS 904L Corrosion Resistance — Element by Element
Each alloying addition has a job. Knowing which one protects against your medium is the quickest way to judge whether 904L fits.
About 25% nickel gives far better resistance to chloride cracking than 316L.
4–5% molybdenum lifts pitting resistance to a PREN of about 35.
Copper is what makes 904L the stainless steel of choice for dilute sulphuric acid.
Very low carbon limits carbide precipitation, so welds keep their corrosion resistance.
How your 904L fasteners order runs
- 01Enquiry review — we confirm size, standard edition and documents against your MR or drawing.
- 02Heat selection & PMI — the mill certificate is checked and material is PMI-tested before processing.
- 03Processing — cutting, machining or bevelling to your specification, with heat numbers marked.
- 04Inspection — your third-party inspector witnesses, or we share photos and test reports.
- 05Packing & dispatch — seaworthy packing from Nhava Sheva (JNPT), Mumbai, FOB or CIF, documents sent before the vessel sails.
Welding & Fabricating SS 904L Fasteners
SS 904L welds by all common arc processes. A few points our buyers ask about:
| Matching filler | ER385 (AWS A5.9) |
|---|---|
| Over-alloyed filler | ERNiCrMo-3 for severe chloride service |
| Preheat | Not required; keep interpass temperature low |
| Cutting | Thermal or abrasive cutting; grind off heat-tinted edges before welding |
Follow your approved WPS; this is general guidance. See also 904L fittings and 904L flanges for the matching pipe-system parts.
How to Order SS 904L Fasteners: RFQ Checklist
Get an accurate quote the first time. Copy this list into your enquiry:
- Fastener type, size and length
- Thread form
- Material and marking
- Quantity in sets
- Certificate type
- Delivery port and date
SS 904L fasteners for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiSS 904L fasteners — questions buyers ask
Is SS 904L the same as Alloy 904L?
Yes. Alloy 904L, UNS N08904, W.Nr 1.4539 all refer to the same material, and fasteners is ordered to ASTM A479 whichever name is on the enquiry.
Why use SS 904L bolts instead of B7 carbon steel?
On SS 904L flanges in corrosive service, carbon-steel bolts corrode first. Matching-alloy bolting avoids galvanic corrosion and bolt failure.
What nut goes with SS 904L stud bolts?
A heavy hex nut machined from the same SS 904L bar (ASTM A479), unless the project specifies otherwise.
How do I stop SS 904L bolts galling?
Use an anti-seize compound on threads and nut faces, tighten at moderate speed, and do not reuse galled nuts.
SS 904L or Inconel 825 — which should I choose?
SS 904L is chosen for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. Inconel 825 is the step up when you need more pitting resistance or strength. See the comparison table on this page, or ask us with your process conditions.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026