Hangbo Alloy Group
Shanghai · Est. 2012
N08024 technical guide: nominal chemical composition, mechanical and physical properties, corrosion resistance, welding, product forms and ASTM standards...
Alloy 20Mo-4 (UNS N08024) is a nickel-iron-chromium-molybdenum-copper alloy. Higher-Mo Alloy 20 for stronger acid resistance. Nb stabilises welds against 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 Alloy 20Mo-4 for a project.
Alloy 20Mo-4 belongs to the nickel-iron-chromium-molybdenum-copper alloy class of materials. It is higher-mo alloy 20 for stronger acid resistance. It is nb stabilises welds against sensitisation. It is excellent in sulphuric acid service.
Nominal (wt%) composition of Alloy 20Mo-4 (UNS N08024):
| Element | Composition (wt%) |
|---|---|
| Nickel (Ni) | 35.0 – 40.0 |
| Chromium (Cr) | 22.0 – 25.0 |
| Iron (Fe) | Balance |
| Molybdenum (Mo) | 3.0 – 4.0 |
| Copper (Cu) | 1.0 – 2.0 |
| Niobium (Nb) | 0.15 – 0.45 |
| Carbon (C) | ≤ 0.03 |
| Manganese (Mn) | ≤ 1.0 |
| Silicon (Si) | ≤ 0.75 |
| Sulphur (S) | ≤ 0.035 |
| Phosphorus (P) | ≤ 0.035 |
Typical physical properties:
| Property | Value |
|---|---|
| Density | 8.05 g/cm³ |
| Melting Range | 1300 – 1400 °C |
| Thermal Expansion (20–1000 °C) | 15.0 µm/m·K |
| Thermal Conductivity (100 °C) | 12.0 W/m·K |
| Modulus of Elasticity | 195 GPa |
Typical room-temperature mechanical properties (annealed / specified condition unless noted):
| Property | Typical Value |
|---|---|
| Tensile Strength (Rm) | 550 MPa (80 ksi) |
| Yield Strength, 0.2% (Rp0.2) | 240 MPa (35 ksi) |
| Elongation in 50 mm | 40% |
| Hardness (Rockwell B) | 75 – 90 HRB |
| Property | Value |
|---|---|
| Service temperature | Cryogenic to ≈ 500 °C |
Its pitting resistance equivalent number (PREN) is approximately ≈ 30, placing it among the more locally-corrosion-resistant grades for chloride service. 20Mo-4 is a higher-molybdenum evolution of the classic Alloy 20, adding molybdenum to 3–4 % for improved resistance to reducing acids, particularly sulphuric acid, while niobium stabilises welds against sensitisation. It resists pitting and intergranular attack better than standard 20.
Welded with matching ERNiCrMo-?? or 20-type fillers; niobium + low carbon prevent weld sensitising, so post-weld heat treatment is not required for corrosion service.
The grade is supplied to the following common specifications:
| Standard | Product Form / Scope |
|---|---|
| ASTM B463 | Plate, sheet & strip |
| ASTM B464 | Welded pipe |
| ASTM B468 | Welded tube |
| ASTM B366 | Fittings |
Standards & References. Specifications cited on this page; confirm current revisions with the issuing body.
General references: Nickel Institute · AMPP (corrosion) · SAE International · ASTM International
20Mo-4 is a higher-molybdenum version of Alloy 20, raising molybdenum to 3–4 % for improved resistance to reducing acids such as sulphuric acid, with niobium added to keep welds immune to sensitisation.
Annealed: ≈ 550 MPa tensile, ≈ 240 MPa yield, 40 % elongation, 75–90 HRB.
20Mo-4 lifts molybdenum (3–4 % vs ~2–3 %) and adds niobium, improving resistance to pitting and intergranular corrosion in acid service while keeping the same fabrication friendliness.
Yes, with matching or 20-type fillers; low carbon plus niobium prevent weld sensitising, so post-weld heat treatment is generally not needed.
Sulphuric acid storage/handling, pharmaceutical and food vessels, acid-service heat exchangers, pickling equipment and acid-transfer tank trailers.
Plate/sheet/strip ASTM B463, welded pipe B464, welded tube B468, fittings B366.
As a dedicated nickel alloy manufacturer serving chemical processing, marine 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.