Hiduron Magnetic Permeability

The Cu-Ni-Al matrix is FCC austenitic copper-nickel; the strengthening precipitate is the FCC gamma-prime Ni3Al phase, which is also non-magnetic. The iron addition is held in solid solution rather than precipitating as a ferritic or martensitic phase; controlling the iron at 1.0 to 2.0 percent on Hiduron 130 and 0.5 to 1.5 percent on Hiduron 191 keeps the Fe-rich phase suppressed through the solution-anneal plus age cycle. Cold-work induced martensite is not a concern because the Cu-Ni-Al matrix does not transform to BCC under cold work the way 316L austenitic stainless does. The result is that the permeability reading on the finished bolt or stud stays inside the mu_r below 1.005 envelope across the supply chain, against the mu_r below 1.10 limit that Monel K-500 cannot beat.

The UK Royal Navy and the US Navy procure Hiduron 191 bolting for surface mine-countermeasure (MCM) vessels and for submarine control elements where the bolt body must not perturb the local magnetic field. The procurement specs (NES 835, DEF STAN 02-835, DOD-C-24676) call out the mu_r below 1.005 limit on every heat as a release condition, alongside the standard chemistry, mechanicals, hardness and SCC requirements. The certificate reports the permeability reading on the test piece. Hiduron 130 is also procured into MCM and submarine bolting on the same non-magnetic basis where the lower strength is acceptable. The combination of non-magnetic response, NACE compliance and seawater corrosion resistance is what makes the alloy the procurement default on naval bolting where Monel K-500 and 316L are both excluded by the magnetic-permeability limit.

Aerospace electromagnetic-sensitive bolting (radar housing, antenna mount, magnetometer hardpoint) needs the same mu_r below 1.005 envelope to avoid perturbing the local field. Hiduron 130 (DTD 900/4805 origin spec) was developed for the UK Air Ministry on this basis and is procured into airframe applications where the bolt body must not affect avionics readings. The seawater corrosion performance is a secondary benefit on naval aircraft (carrier-based fixed-wing, anti-submarine helicopters) where saltwater exposure adds the corrosion duty to the non-magnetic duty.

Every Hiduron 130 and Hiduron 191 stock and finished fastener ships with EN 10204 type 3.1 mill test certificate as standard. Type 3.2 third-party witness by Lloyd's Register, DNV, BV, SGS or TUV is supplied on call-out and is standard practice on naval and subsea procurement orders. The certificate carries the melt heat number, full chemical analysis to the controlling specification, solution-anneal plus age cycle parameters, tensile and yield results, hardness, Charpy V impact result where called out, and the dimensional report. For Hiduron 191 sour-service orders, an additional NACE MR0175 hardness certificate confirms that every test piece reads below the 286 HBW (28 HRC) limit.

TorqBolt supplies Hiduron 130 (UNS C72400, DTD 900/4805) and Hiduron 191 (UNS C72420, NES 835, DEF STAN 02-835, DOD-C-24676) in round bar, stud bolts, hex bolts, heavy hex bolts, nuts, washers, forgings and machined components. Standard fastener lead time is 4 to 8 weeks from order, subsea machined components quote project-specific lead time. Send an enquiry through TorqBolt Contact with the controlling specification, the form factor, the size envelope and the certification level (3.1 default, 3.2 on call-out, NACE on call-out).

Request a Quote on Hiduron 130 and Hiduron 191 Bolting Stock and Fasteners

Q. Is Hiduron non-magnetic?
Yes. Both Hiduron 130 and Hiduron 191 carry relative magnetic permeability mu_r below 1.005 on the standard cycle, with selected naval-grade heats reading below 1.001. The alloy is procurement-qualified for UK Royal Navy and US Navy mine-countermeasure and submarine bolting.

Q. What is the magnetic permeability limit on naval bolting?
NES 835, DEF STAN 02-835 and DOD-C-24676 call out mu_r below 1.005 as the release condition on every heat. The reading is reported on the EN 10204 type 3.1 mill test certificate.

Q. Why is Monel K-500 excluded from MCM bolting?
Monel K-500 carries mu_r of 1.05 to 1.10, which exceeds the mu_r below 1.005 limit for naval mine-countermeasure and submarine bolting. Hiduron 191 is the direct NACE-qualified, non-magnetic replacement for K-500 on this duty.

Q. Does cold work raise the Hiduron permeability?
No. The Cu-Ni-Al matrix does not transform to BCC under cold work the way 316L austenitic stainless does. The permeability stays inside the mu_r below 1.005 envelope on cold-rolled, machined and threaded product.