Ferralium 255 Fg46 Acorn Nuts Specification

Ferralium 255 Fg46 Acorn Nuts Equivalent Designation
| UNS Designation | British STD | Werkstoff No. | European STD | Swedish STD | Japanese STD | Forging |
|---|---|---|---|---|---|---|
| S32520 | – | 1.4507 | X2CrNiMoCuN25-6-3 | – | – | Sa 182 F61 |
Ferralium 255 Fg46 Acorn nuts are internally threaded fasteners that mate with bolts and studs to form clamped joints. TorqBolt manufactures Ferralium 255 Fg46 Acorn nuts per ASME B18.2.2, ISO 4032/4033/4034, DIN 934/EN 24032, and DIN 6915 (heavy hex), in sizes M6–M100 and 1/4"–4".
For vibration-loaded joints, Ferralium 255 Fg46 Acorn nuts are available as nyloc (polymer insert), all-metal prevailing-torque (DIN 980, distorted-thread style), flange-serrated (DIN 6923, integral washer face with anti-back-off teeth), and castle / slotted (DIN 935, cotter-pin retention). Each locking style trades reusability against prevailing-torque retention.
Ferralium 255 Fg46 Acorn nut threads are gauged per ASME B1.1 / ISO 965 to Class 2B / 6H by default; high-strength variants use 3B / 4H6H. Proof-load testing per ASTM F606 verifies the nut can develop the bolt's full strength without thread strip; hardness range is controlled to prevent stress-corrosion susceptibility (HV 250–353 typical for high-grade nuts). Each lot is EN 10204 3.1 / 3.2 certified.
TorqBolt also produces Ferralium 255 Fg46 Acorn nuts in weld-nut, T-nut, square-nut, knurled thumb-nut, and rivet-nut patterns. NACE MR0175 / ISO 15156 sour-service certification available; NORSOK M-650 qualified mills supplying high-temperature service grades.
Duplex stainless steels have a roughly 50/50 ferrite-austenite microstructure, doubling the yield strength of austenitic 304/316 grades while improving chloride pitting + stress-corrosion resistance. Duplex is the modern default for offshore platform fasteners, desalination plants, and sour-gas piping where austenitics fail to chloride SCC and martensitics fail to hydrogen embrittlement.
Duplex 2205 (UNS S32205 / S31803) is the standard grade with PREN ~35, suitable for chloride-bearing service to ~250°C. Super Duplex 2507 (S32750) and Zeron 100 (S32760) push PREN to 41-42 with higher Cr+Mo+N, qualifying for the most aggressive seawater + sour-well environments. SA-182 F51 / F53 / F55 / F60 are the ASME forged-flange equivalents.
Phase balance is critical: ferrite content must stay within 35-65% in weld + HAZ to maintain corrosion + impact properties (ASTM A923 testing). Solution anneal at 1040-1100°C followed by water quench locks the duplex microstructure. Fasteners ship per ASTM A276 / A479 with EN 10204 3.1 / 3.2 certs including ferrite count and Charpy impact at -46°C. NACE MR0175 / ISO 15156 sour-service certification is standard.