Bar and Rod
Plate and Sheet
Strip
Pipe and Tube
Wire
Welding
Powder Material
Cast Products
Forged Products
Fittings
Fastening
Round Bar:
φ2–500 mm, 1–6 m length
Flat/Square Bar:
4–100 mm thickness/width
Hex Bar:
A/F 3–100 mm
Hollow Bar:
OD 20–300 mm
Sheet:
0.3–6 mm thickness
Medium Plate:
6–25 mm thickness
Heavy Plate:
25–100 mm thickness
Standard Strip:
0.05–3 mm thick,
10–600 mm wide
Precision strip:
0.01–0.5 mm thick,
tight tolerance ±0.005 mm
Foil:
0.005–0.1 mm thick
Seamless Tube:
OD 6–450 mm,
WT 1–50 mm,
1–12 m length
Welded Tube:
OD 10–600 mm,
WT 1–20 mm
Capillary Tube:
OD 1–10 mm,
WT 0.1–2 mm
Wire Form:
Cold Drawn Wire,
Bright Wire,
Spring Wire,
Fine Wire,
Ultra-fine Wire
General Diameter:
φ0.1–10 mm
Coil Weight:
50–500 kg,
customizable tolerance
Solid Wire:
φ0.8–4.0 mm
Flux-cored Wire:
φ1.2–4.0 mm
Welding Rod:
φ2.0–5.0 mm
Powder Form:
AM 3D Printing Powder,
Spherical Powder,
Gas-atomized Powder,
Water-atomized Powder
Particle Size:
10–150 μm
Sphericity:
≥90% for AM grade
Cast Ingot:
φ200–800 mm
Precision Casting:
min wall 0.5 mm
Cast Pipe:
OD 100–600 mm,
WT 10–50 mm
Forged Bar:
Φ35–500 mm
Forged Ring:
OD 200–2000 mm
Forging Weight:
1–5000 kg
Fittings Form:
Elbow, Tee, Reducer, Flange, Cap, Outlet, Lap Joint
Size range:
1/2''–24'' (DN15–DN600)
Wall thickness:
Sch10–Sch160, STD, XS, XXS
Pressure Class:
150–2500 LB
Fastening Form:
Bolt, Nut, Screw, Stud, Washer, Pin, Rivet
Metric: M3–M64
Imperial: #4–2.5''
Length: 6–500 mm
Alloy 20 is an iron–nickel–chromium–molybdenum–copper austenitic alloy (niobium-stabilised) developed for outstanding resistance to sulphuric acid and a wide range of corrosive chemical environments, including both oxidising and reducing conditions. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
The copper and molybdenum additions give exceptional resistance to sulphuric and phosphoric acids; the high nickel content provides resistance to chloride-ion stress-corrosion cracking; and niobium stabilisation (Nb = 8 × C to 1.0 %) prevents sensitisation and intergranular attack in welded joints. It also offers useful resistance to nitric acid and to pitting and crevice corrosion — better than 304 stainless and comparable to 316L, while solving the chloride stress-corrosion-cracking problems that affect 316L.
The alloy is readily fabricated into mixing tanks, heat exchangers, process piping, pickling equipment, pumps, valves, fasteners and fittings, and is widely used in the production of gasoline, solvents, explosives, inorganic and organic chemicals, pharmaceuticals, and food and synthetic materials. Its aqueous-corrosion applications are essentially the same as those for the more highly alloyed 825-type material, at lower cost. It is included in NACE MR0175 for sour-service oil-field equipment.
Values per Special Metals official datasheet, annealed condition.
| Property | Value | Unit |
|---|---|---|
| Density | 8.08 | g/cm³ |
| Young's modulus | 193 | GPa |
| Shear modulus | 76 | GPa |
| Specific heat capacity | 500 | J/kg·K |
| Electrical resistivity | 1.08 | µΩ·m |
| Thermal conductivity | 12.3 | W/m·K |
| Coefficient of thermal expansion (25–100 °C) | 14.7 | µm/m·°C |
| Maximum service temperature (continuous) | ~800 | °C |
Limiting composition per ASTM B462 / B463 (UNS N08020).
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element; austenitic matrix; cost-effective |
| Nickel | Ni | 32.0 | 38.0 | Chloride SCC resistance; austenite stabiliser |
| Chromium | Cr | 19.0 | 21.0 | Oxidising-acid resistance; passive film |
| Copper | Cu | 3.0 | 4.0 | Key addition; sulphuric-acid resistance |
| Molybdenum | Mo | 2.0 | 3.0 | Pitting/crevice and reducing-acid resistance |
| Niobium (+ Tantalum) | Nb | 8×C | 1.0 | Stabiliser; prevents weld sensitisation |
| Carbon | C | — | 0.07 | Controlled |
| Manganese | Mn | — | 2.0 | Deoxidiser |
| Silicon | Si | — | 1.0 | Deoxidiser |
| Phosphorus | P | — | 0.045 | Residual impurity |
| Sulphur | S | — | 0.035 | Residual impurity |
Typical room-temperature properties, annealed condition.
| Property | Value | Source |
|---|---|---|
| Ultimate tensile strength | 620 MPa (90 ksi) | Special Metals datasheet |
| 0.2% proof strength (yield) | 300 MPa (45 ksi) | Special Metals datasheet |
| Elongation at break | 40 % | Special Metals datasheet |
| Hardness (annealed) | ~B83 HRB | Special Metals datasheet |
Cold work substantially raises strength: at 50 % cold reduction, UTS reaches ~1017 MPa and yield ~962 MPa (hardness ~C30). The alloy is not age-hardenable; higher strength is achieved by cold work. Values are typical; confirm against the mill test certificate for each delivery.
| Environment | Performance | Notes |
|---|---|---|
| Sulphuric acid (H₂SO₄) | Outstanding | Copper addition gives exceptional resistance across wide concentration range |
| Phosphoric acid | Excellent | Suitable for fertiliser and process duty |
| Nitric acid | Very Good | Passes boiling 65% nitric acid test (annealed and sensitised) |
| Chloride stress-corrosion cracking | Excellent | High Ni content; passes boiling 42% MgCl₂ test |
| Pitting and crevice corrosion | Good | Better than 304; comparable to 316L |
| Intergranular corrosion | Excellent | Niobium stabilisation prevents sensitisation |
| Sulphide stress cracking | Excellent | Included in NACE MR0175 (Rockwell C 32 max) |
| Reducing media | Good | Ni + Mo content |
The alloy is niobium-stabilised austenitic and is NOT age-hardenable. Heat treatment is for annealing only; strength is increased by cold work.
Anneal Temperature: 982–1010 °C (1800–1850 °F), time commensurate with section size Cooling: Air cool Purpose: Softening, recrystallisation, and restoration of corrosion resistance.
Hot Forming Temperature: 760–1175 °C (1400–2150 °F)
Stabilise Anneal is used to optimise resistance to intergranular attack for welded service.
Readily joined by conventional welding processes. Niobium stabilisation minimises weld-zone sensitisation. Matched or overmatched nickel-alloy filler metals are used.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Excellent | AWS A5.14 ERNiCrMo-3 (overmatching) |
| GMAW / MIG | Good | AWS A5.14 ERNiCrMo-3 (overmatching) |
| SMAW / stick | Good | AWS A5.11 ENiCrMo-3 |
Overmatching Ni-Cr-Mo filler metals are commonly used to offset elemental segregation in the weld and ensure the joint matches base-metal corrosion resistance.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Work hardening | Moderate; austenitic behaviour, similar to stainless |
| Tooling | Sharp, rigid setup; carbide or HSS |
| Coolant | Flood coolant recommended |
| Preferred condition | Annealed |
Forming Processes
| Process | Notes |
|---|---|
| Hot forming | 760–1175 °C |
| Cold forming | Readily formed; tensile rises sharply with cold work (UTS up to ~1017 MPa at 50% reduction) |
| Annealing between operations | 982–1010 °C for heavy reductions |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Chemical processing | Mixing tanks, heat exchangers, process piping, pickling equipment | Sulphuric/phosphoric acid resistance |
| Pharmaceutical | Reaction vessels, process equipment | Broad-spectrum corrosion resistance; cleanliness |
| Petrochemical / oil & gas | Pumps, valves, fasteners, fittings; sour-service hardware | Acid + chloride resistance; NACE MR0175 |
| Food and synthetic materials | Processing equipment | Corrosion resistance, hygiene |
| Pickling / plating | Tanks and equipment for acid service | Sulphuric-acid resistance |
| Product Form | ASTM Standard | ASME Code |
|---|---|---|
| Rod, bar and forging stock | ASTM B462 / B472 / B473 | ASME SB-462 / SB-472 / SB-473 |
| Plate, sheet and strip | ASTM A240 / B463 / B906 | ASME SA-240 / SB-463 |
| Seamless pipe and tube | ASTM B729 / B468 / B464 | ASME SB-729 / SB-468 / SB-464 |
| Welded pipe / tube | ASTM B474 / B751 / B775 | ASME SB-474 / SB-751 |
| Fittings | ASTM B366 | ASME SB-366 |
| Welding consumables | AWS A5.14 ERNiCrMo-3 (overmatching) | — |
Listed in NACE MR0175 for sour-service (Rockwell C 32 max).
| Alloy | Ni % | Cr % | Mo % | Other | Best Used For |
|---|---|---|---|---|---|
| Alloy 20 | 32–38 | 19–21 | 2–3 | Cu 3–4 | Sulphuric acid; chemical process; SCC resistance |
| Alloy 825 | 38–46 | 19.5–23.5 | 2.5–3.5 | Cu 1.5–3 | Higher-Ni acid resistance; phosphoric/sulphuric |
| Alloy 625 | ≥58 | 20–23 | 8–10 | Nb 3.15–4.15 | Sea-water; universal corrosion + strength |
| Alloy C-276 | bal | 14.5–16.5 | 15–17 | W 3–4.5 | Severe reducing acids; far higher Mo |
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