Super duplex 25Cr-7Ni-3.5Mo-0.7Cu-0.7W-0.25N · PREN ≥ 40 · CPT ≥ 50°C per ASTM G48 Method E · Sigma-phase free per A923 Method C
F55 is the ASTM A182 designation for the super duplex stainless steel forging grade matching UNS S32760 (Werkstoff 1.4501, also known by the trade name Zeron 100). The W (tungsten) and Cu (copper) additions distinguish F55 from the rest of the super duplex family: tungsten lifts pitting resistance equivalent number to PREW ≈ 41.5 and improves chloride resistance; copper improves performance in mildly reducing acids (HCl, dilute H2SO4). The grade is qualified for North Sea service per NORSOK M-650 with M-630 MDS 055 acceptance, and for sour-service downhole + wellhead components per NACE MR0175 / ISO 15156-3.
F55 chemistry per ASTM A182: C max 0.030, Cr 24.0-26.0, Ni 6.0-8.0, Mo 3.0-4.0, Cu 0.50-1.00, W 0.50-1.00, N 0.20-0.30, balance Fe.
| Property | Value (Solution Annealed) | Test |
|---|---|---|
| 0.2% Yield strength (Rp0.2) | ≥ 550 MPa (80 ksi) | ASTM E8 / E8M tensile |
| Ultimate tensile strength (Rm) | ≥ 750 MPa (109 ksi) | ASTM E8 / E8M tensile |
| Elongation (A) | ≥ 25% | ASTM E8 / E8M, 4D gauge |
| Hardness (sour-service cap) | ≤ 28 HRC | NACE MR0175 |
| Charpy V-notch impact, RT | ≥ 45 J avg, 35 J min | ASTM E23, 3 specimens |
| Charpy V-notch impact, -46°C | ≥ 45 J avg (FLT path) | ASTM E23, 3 specimens |
| Ferrite content | 35-55% (parent metal) | ASTM E562 point count |
| CPT critical pitting temp | ≥ 50°C | ASTM G48 Method E |
| PREN | ≥ 40 | Cr + 3.3(Mo + 0.5W) + 16N |
Solution anneal at 1100-1140°C with hold time proportional to section thickness (minimum 30 minutes per 25 mm), followed by rapid water quench to room temperature. The water quench skips the precipitation nose for sigma + chi + Cr2N at 600-1000°C; without it, brittle intermetallics grow in the ferrite phase and the impact + corrosion envelope collapses. ASTM A923 Method C (Charpy V-notch at RT on a witness coupon) is the production gate, ≥ 60 J validates that the anneal succeeded.
| Service | Why F55 over F51 (2205) or F44 (6Mo) |
|---|---|
| FPSO topside flanges + manifolds | Saltwater spray + sour-process content, F55's W + Cu lifts chloride + reducing-acid resistance vs F51 |
| Subsea manifold + jumper flanges | Deepwater chloride at low temperature, F55 holds Charpy at -46°C; 6Mo loses toughness |
| API 6A wellhead bonnets + master valves | HPHT sour-service with H2S above NACE MR0175 thresholds, F55 sits inside the qualified envelope |
| Desalination RO membrane vessel flanges | Concentrated brine + cyclic pressure, CPT ≥ 50°C avoids crevice corrosion at flange faces |
Send the spec (component + size + ASME class + supplementary requirements such as low-temp Charpy, NDT, MDS-055 acceptance + quantity + destination port) to info@torqbolt.com or +91-22-66157017 / WhatsApp. Cross-reference: Zeron 100 forgings hub, ASTM A182 family, FG fastener-grade, SA supply state.
