Hangbo Alloy Group
Shanghai · Est. 2012
N08904 technical guide: nominal chemical composition, mechanical and physical properties, corrosion resistance, welding, product forms and ASTM standards...
904L (UNS N08904) is a super-austenitic stainless (high ni + cu + mo). High Ni + Cu + Mo for dilute acid service. Extra-low carbon → no sensitisation. This guide covers its nominal chemical composition, typical mechanical and physical properties, corrosion behaviour, welding, common applications, available product forms and the ASTM standards that apply — everything a specifier needs to evaluate 904L for a project.
904L belongs to the super-austenitic stainless (high ni + cu + mo) class of materials. It is high ni + cu + mo for dilute acid service. It is extra-low carbon → no sensitisation. It is better than 316l in chlorides & sulphuric acid.
Nominal (wt%) composition of 904L (UNS N08904):
| Element | Composition (wt%) |
|---|---|
| Nickel (Ni) | 23.0 – 28.0 |
| Chromium (Cr) | 19.0 – 23.0 |
| Molybdenum (Mo) | 4.0 – 5.0 |
| Copper (Cu) | 1.0 – 2.0 |
| Iron (Fe) | Balance |
| Carbon (C) | ≤ 0.020 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 |
| Sulphur (S) | ≤ 0.035 |
Typical physical properties:
| Property | Value |
|---|---|
| Density | 7.95 g/cm³ |
| Melting Range | 1300 – 1400 °C |
| Thermal Expansion (20–1000 °C) | 15.5 µm/m·K |
| Thermal Conductivity (100 °C) | 13.0 W/m·K |
| Electrical Resistivity | 0.95 µΩ·m |
| Modulus of Elasticity | 195 GPa |
Typical room-temperature mechanical properties (annealed / specified condition unless noted):
| Property | Typical Value |
|---|---|
| Tensile Strength (Rm) | 490 MPa (71 ksi) |
| Yield Strength, 0.2% (Rp0.2) | 215 MPa (31 ksi) |
| Elongation in 50 mm | 35% |
| Hardness (Rockwell B) | 70 – 90 HRB |
| Property | Value |
|---|---|
| Service temperature | Cryogenic to ≈ 400 °C |
| Service note | PREN ≈ 36 |
Its pitting resistance equivalent number (PREN) is approximately ≈ 36, placing it among the more locally-corrosion-resistant grades for chloride service. 904L is a high-nickel, copper- and molybdenum-bearing austenitic stainless developed for service in dilute sulphuric and phosphoric acids and in chloride-bearing environments where 316L fails. The very low carbon gives immunity to sensitisation, and the copper aids resistance to reducing acids.
Welded with matching 904L fillers (or 20-type) keeping heat input moderate; the extra-low carbon avoids sensitisation, so post-weld heat treatment is not needed for corrosion service.
The grade is supplied to the following common specifications:
| Standard | Product Form / Scope |
|---|---|
| ASTM A240 | Plate, sheet & strip |
| ASTM A312/A358 | Pipe |
| ASTM A182 | Flanges & forgings |
| ASTM A276 | Bar |
Standards & References. Specifications cited on this page; confirm current revisions with the issuing body.
General references: Nickel Institute · AMPP (corrosion) · SAE International · ASTM International
904L (UNS N08904) is a high-nickel, copper- and molybdenum-bearing austenitic stainless for dilute sulphuric and phosphoric acids and chloride environments where 316L fails. Its extra-low carbon gives immunity to sensitisation.
Annealed: ≈ 490 MPa tensile, ≈ 215 MPa yield, 35 % elongation, 70–90 HRB.
904L has much higher nickel, plus copper and more molybdenum, so it resists dilute sulphuric/phosphoric acids and chlorides far better than 316L, at higher cost.
Yes, with matching 904L (or 20-type) fillers and moderate heat input; the extra-low carbon prevents sensitisation, so no post-weld heat treatment is needed.
Dilute acid plant, pulp/paper digestors and bleach, seawater-cooled condensers, FGD hardware and pharma/food vessels.
Plate/sheet/strip ASTM A240, pipe A312/A358, flanges/forgings A182, bar A276.
As a dedicated nickel alloy manufacturer serving chemical processing, marine, power generation sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.