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 F255 is a copper-bearing super duplex stainless steel — historically the first super duplex grade — with a microstructure of roughly equal ferrite and austenite. This datasheet presents the material within the American standard system.
With about 25% chromium, 5.5% nickel, 3.4% molybdenum, a deliberate copper addition (~2%) and nitrogen, Alloy F255 has a pitting-resistance equivalent number (PREN) of about 40, giving outstanding resistance to chloride pitting, crevice corrosion and stress-corrosion cracking, with a critical pitting temperature above 50 °C. The ~2% copper distinguishes it from other super duplex grades and gives improved resistance to reducing acids (sulphuric, hydrochloric). It offers roughly double the yield strength of austenitic grades, with good ductility and impact strength down to sub-zero temperatures.
Typical applications include seawater systems, oil-and-gas downhole and subsea equipment, desalination plant, chemical-process equipment, and high-strength corrosion-resistant components.
| Property | Value | Unit |
|---|---|---|
| Density | 7.8 | g/cm³ |
| Melting range | 1350-1400 | °C |
| Young's modulus (20 °C) | 210 | GPa |
| Thermal conductivity (20 °C) | 14 | W/m·K |
| Coefficient of thermal expansion (20-100 °C) | 12 | µm/m·°C |
| Specific heat (20 °C) | 490 | J/kg·K |
| Maximum continuous service temperature | ~275 | °C |
| Magnetic response | Ferromagnetic (duplex) | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element |
| Chromium | Cr | 24.0 | 27.0 | Ferrite former; corrosion resistance |
| Nickel | Ni | 4.5 | 6.5 | Austenite former; phase balance |
| Molybdenum | Mo | 2.9 | 3.9 | Pitting + crevice resistance |
| Copper | Cu | 1.5 | 2.5 | Reducing-acid resistance |
| Nitrogen | N | 0.10 | 0.25 | Austenite former; strength; pitting |
| Manganese | Mn | — | 1.5 | Deoxidiser |
| Silicon | Si | — | 1.0 | Deoxidiser |
| Carbon | C | — | 0.04 | Low (intergranular resistance) |
| Phosphorus | P | — | 0.040 | Residual impurity |
| Sulphur | S | — | 0.030 | Residual impurity |
Solution-annealed condition, per ASTM A240 for UNS S32550.
| Property | Value | Unit |
|---|---|---|
| Tensile strength | >=760 | MPa |
| 0.2% yield strength | >=550 | MPa |
| Elongation at break | >=15 | % |
| Brinell hardness | <=302 | HB |
| Rockwell hardness | <=32 | HRC |
Confirm against the mill test report.
| Environment | Performance | Notes |
|---|---|---|
| Chloride pitting | Outstanding | PREN ~40; CPT > 50 °C |
| Crevice corrosion | Outstanding | High Cr + Mo + N |
| Chloride SCC | Excellent | Duplex structure |
| Reducing acids (H₂SO₄, HCl) | Excellent | ~2% copper addition |
| Seawater | Excellent | Warm chlorinated seawater |
| Sulphide / sour | Good | Listed in NACE MR0175 |
The 2% copper gives better reducing-acid resistance than other super duplex grades.
Not hardenable by heat treatment; properties are set by solution annealing and phase balance.
Solution Anneal approximately 1080-1120 °C, followed by rapid water quench to retain the balanced ferrite-austenite structure and avoid embrittling intermetallic phases. Rapid cooling is critical owing to the high alloy content. Avoid prolonged exposure in the 300-1000 °C range (sigma-phase / 475 °C embrittlement).
Weldable by common fusion methods; use a matching or over-alloyed super-duplex filler and control heat input to maintain phase balance.
| Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Good | Matching super-duplex (25 Cr Cu type) |
| GMAW / MIG | Good | Super-duplex filler |
| SMAW / stick | Good | Matching super-duplex electrode |
No preheat; control interpass temperature (typically <=150 °C) and heat input; a balanced weld maintains corrosion resistance and the absence of intermetallic phases.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Machinability | Difficult; high strength + work-hardening; rigid setup, carbide tools, low speeds |
| Work hardening | High rate; positive feeds, avoid dwelling |
| Coolant | Ample flood coolant |
Forming Processes
| Process | Notes |
|---|---|
| Hot forming | ~1200-1000 °C; solution anneal + quench afterward |
| Cold forming | Higher forces than standard duplex (very high strength) |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Marine / seawater | Pumps, valves, propeller shafts | Warm chloride + erosion resistance |
| Oil & gas | Downhole, subsea, components | Pitting + sour-service resistance |
| Chemical processing | Acid equipment (H₂SO₄, HNO₃, H3PO4) | Reducing-acid resistance (Cu) |
| Desalination | Pumps, heat exchangers | Hot chloride resistance |
| Product Form | Standard | Notes |
|---|---|---|
| Plate, sheet and strip | ASTM A240 / ASME SA-240 · UNS S32550 | — |
| Forgings / fittings / flanges | ASTM A182 | — |
| Bar and shapes | ASTM A276 / A479 · UNS S32550 | — |
| Seamless / welded tube | ASTM A789 · UNS S32550 | — |
| Seamless / welded pipe | ASTM A790 · UNS S32550 | — |
| Sour service | NACE MR0175 / ISO 15156 | Acid-gas applications |
Copper-bearing 25Cr super duplex stainless steel. UNS S32550.
| UNS | Cr % | Ni % | Mo % | Cu % | N % | Best Used For |
|---|---|---|---|---|---|---|
| Alloy F255 | 24-27 | 4.5-6.5 | 2.9-3.9 | 1.5-2.5 | 0.10-0.25 | Cu-bearing super duplex; acids + seawater |
| S32520 | 24-26 | 5.5-8.0 | 3.0-5.0 | 0.5-3.0 | 0.20-0.35 | Cu/N super duplex |
| S32506 | 24-26 | 5.5-7.2 | 3.0-3.5 | — | 0.08-0.20 | W-bearing duplex (low Cu) |
| S32750 | 24-26 | 6.0-8.0 | 3.0-5.0 | — | 0.24-0.32 | Super duplex (no Cu) |
| S32205 | 22-23 | 4.5-6.5 | 3.0-3.5 | — | 0.14-0.20 | Standard duplex |
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