2.4669 forgings Forged rings, flanges, bars, discs and shafts in Alloy X-750 / UNS N07750 / NiCr15Fe7TiAl

2.4669 is not a separate alloy from Alloy X-750. It is the same material recorded under the European numbering system. Buyers meet it as 2.4669 on German and EU drawings, as UNS N07750 in ASTM and AMS documents, and as Inconel® X-750 in Special Metals literature.

The alloy is a solid-solution nickel–chromium matrix made age hardenable by roughly 2.5 % titanium and 0.7 % aluminium, with a small niobium addition. During ageing these elements precipitate the coherent γ′ phase Ni₃(Ti, Al), which is what raises tensile strength from about 700 MPa in the solution annealed condition to over 1 100 MPa after heat treatment. Chromium provides the oxidation and hot-corrosion resistance; the high nickel content gives resistance to chloride stress-corrosion cracking and good behaviour in steam.

The property most buyers specify it for is relaxation resistance. 2.4669 holds bolt load and spring force at temperature far better than austenitic stainless steel, which is why it is standard in hot fasteners, springs, bellows and turbine hardware.

Where 2.4669 sits against neighbouring grades

Rule of thumb used by our engineering team: below 650 °C choose 2.4668 for strength and weldability; above it, choose 2.4669 for relaxation and oxidation resistance.

Always state the governing specification and the required heat-treated condition on the order. The same 2.4669 chemistry certified to AMS 5667 and to AMS 5671 will have very different mechanical acceptance limits because the ageing route differs.

Limits above follow ASTM B637 for UNS N07750. Our melt shops hold sulfur well under the 0.010 % ceiling because sulfur is the main cause of hot shortness during open-die forging of this alloy. Ladle and product analysis for every heat is reported on the EN 10204 certificate.

Mechanical properties of 2.4669 depend far more on the heat-treated condition than on the chemistry, which is why the condition must be stated on the order. Values below are typical minima for forged bar and ring sections.

Section size matters: heavy ring and disc sections cool more slowly and typically sit 30–60 MPa below thin bar. Stress-rupture acceptance commonly specified for 2.4669 is a minimum life of 23 hours at 732 °C (1350 °F) under 310 MPa (45 ksi). Confirm the exact acceptance criteria against your governing specification before ordering. Our technical department will review your specification free of charge.

Strength retention at temperature

Short-term tensile data must not be used for sustained load above roughly 650 °C. Design to creep and stress-rupture curves for the actual service life.

2.4669 is supplied age hardened. Which ageing route you specify decides both the strength and the temperature at which the part stays stable, so it belongs on the drawing next to the material callout.

Notes from our heat treatment shop: hold times are section-size dependent and are measured from equalisation of the part, not the furnace. Furnace atmosphere must be sulfur free, because sulfur pickup from fuel-fired furnaces embrittles high-nickel alloys. Every charge is run against a calibrated multi-point chart recorder and the chart is issued with the certificate.

Machining and welding guidance

• Rough machine in the solution annealed or equalised condition wherever the tolerance stack allows.
• Fully aged 2.4669 work hardens rapidly, so use positive rake carbide, rigid setups, heavy feeds and low speeds.
• Allow for growth: ageing changes dimensions slightly, so leave finishing stock if ageing follows machining.
• Weld in the annealed condition using GTAW with matching or Alloy 718 filler; strain-age cracking is the main risk.
• Solution treat and re-age after welding on restrained joints to restore properties and relieve residual stress.

2.4669 has a narrow hot working window. Forging it too cold causes cracking, and forging it too hot causes grain-boundary liquation. Our practice is to forge between 1150 °C and 1040 °C, finishing no lower than 925 °C, with reheats rather than pushing a heat too far. Finishing strain is kept high enough to recrystallise the structure so that grain size stays uniform through the section.

Machining allowance, tolerance class and surface finish are agreed per drawing. Finish machined, semi-finished and rough machined deliveries are all available, as are near-net shapes that cut your buy-to-fly ratio on an expensive alloy.

• Gas turbines and aero enginesRotor and casing rings, seal rings, spacers, blade retainers, hot bolting, springs and washers running above the limit of Alloy 718.
• Nuclear powerCore hold-down springs, fuel element spacer grids, control rod and guide tube hardware, and studs where relaxation resistance in steam is decisive.
• Oil, gas and subseaDownhole springs, valve stems and seats, wellhead and Christmas tree components, and packer parts exposed to sour and high-temperature wells.
• Valves and flow controlForged stems, seat rings, bodies and back-seat bushings for ball, gate, globe, check and plug valves in high-temperature service.
• Pressure vessels and heat exchangersTube sheets, forged flanges, nozzles and shell rings for reformers, exchangers and reactor internals.
• Rocket and space hardwareThrust chamber components, gimbal and actuator parts, and high-load fasteners where strength-to-weight at temperature matters.
• Heat treatment and metal formingFurnace fixtures, quench and retort hardware, extrusion tooling and forming dies that must survive repeated thermal cycling.
• Rotating and power transmissionShafts, spindles, gears and compressor rings in turbomachinery, gearboxes and industrial air compressors.

Every 2.4669 order leaves the works with a test dossier tied to one heat number. The list below is what that dossier contains.

• Ladle and product chemical analysis by optical emission and combustion analysis
• Tensile, yield, elongation and reduction of area at room temperature
• Elevated-temperature tensile and stress-rupture testing on request
• Brinell or Rockwell hardness, multiple positions per piece
• Grain size and microstructure, ASTM E112
• Ultrasonic testing to EN 10228-3, SEP 1921, ASTM A388 or AMS 2154
• Liquid penetrant testing to ASTM E165 / EN ISO 3452
• Dimensional report against the customer drawing
• Positive material identification by handheld XRF before packing
• EN 10204 3.1 mill certificate as standard; 3.2 with TUV, SGS, BV, Lloyd's Register or DNV on request

Charpy impact, intergranular corrosion, ferrite or magnetic permeability checks, and customer or end-user witnessed inspection can all be built into the inspection and test plan. Send your ITP with the enquiry and we will mark it up before quoting.