Hiduron Heat Treatment

In the as-rolled or as-forged condition the gamma-prime Ni3Al precipitate exists as coarse particles or stringers in the grain interior and along the grain boundaries. The solution-anneal at 850 to 900 deg C dissolves these particles back into the copper matrix and the water quench freezes the supersaturated solid solution at room temperature. The age at 450 to 500 deg C then re-precipitates the Ni3Al as fine, coherent particles distributed uniformly through the grains, which is the strengthening morphology. The fine coherent precipitate raises the yield by roughly 280 MPa on Hiduron 130 and roughly 380 MPa on Hiduron 191 against the as-solutioned condition. The age also restores ductility relative to the as-rolled or as-forged condition because the precipitation removes the residual hot-work stress.

Solution anneal is run in an air-circulating furnace with thermocouple control at the part centre and at a furnace reference location, with the higher of the two readings holding to the 850 to 900 deg C band. The water quench must drop the part to below 100 deg C inside 60 seconds for sections up to 50 mm; for thicker sections a forced-circulation quench tank with agitation maintains the cooling rate at the section centre. The age is run in a separate furnace at 450 to 500 deg C with tight thermocouple control because the strength response is steep against age temperature; a 25 deg C overshoot drops the peak yield by 40 to 60 MPa. Hardness traverse on the test piece confirms that the cycle achieved the intended precipitation; the certificate reports the cycle parameters alongside the hardness reading.

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. What is the Hiduron solution-anneal temperature?
The standard band is 850 to 900 deg C, hold one hour to each 25 mm of section thickness, then water quench. The quench must drop the part to below 100 deg C inside 60 seconds for sections up to 50 mm to freeze the gamma-prime formers in solid solution.

Q. What is the Hiduron age temperature?
The age is 450 to 500 deg C for 2 to 4 hours followed by air cool. Hiduron 130 typically ages at the upper end (475 to 500 deg C) and Hiduron 191 at the lower end (450 to 480 deg C) to land inside the strength specification band.

Q. Can Hiduron be re-solutioned and re-aged if the first cycle is off-spec?
Yes. The cycle is fully reversible. A re-solutioned and re-aged Hiduron part returns to the standard property envelope with no loss of toughness or fatigue endurance. This is one of the supply-chain advantages of the gamma-prime mechanism.

Q. Should fasteners be aged before or after machining?
For finished bolting, the bar is solution-annealed before machining (soft and machinable condition) and aged after machining to the finished dimension. This sequence avoids the dimensional change associated with the strengthening cycle and lets the age also serve as a stress-relief on the machined surface.