FeNi48 Forgings: Alloy 48 / UNS K94800 Rings, Bars, Discs and Flanges

01What is FeNi48 alloy?

FeNi48 contains about 48 % nickel with the balance iron. At this nickel level the thermal expansion of the alloy is close to that of soft lead and soda-lime glass, so a metal part and a glass part can be heated and cooled together without cracking the seal between them.

Pure iron and pure nickel each expand by roughly 12 to 13 µm/m·°C. In nickel-iron alloys these values do not average out. Magnetostriction works against normal thermal expansion, and the expansion curve falls to a minimum at about 36 % nickel before rising again. That minimum is the Invar effect. FeNi48 sits on the rising part of the curve, at the point where expansion matches common sealing glasses.

The effect is magnetic in origin, so it only holds below the Curie point. Above roughly 480 °C the alloy loses its ferromagnetism and expansion rises quickly. The working limit for FeNi48 thermostats and seals is therefore normally given as 450 °C.

FeNi48 in forged form

FeNi48 is usually stocked as strip, wire and small-diameter bar. Large rings, heavy discs, tube sheets and shafts machined from plate waste a lot of an expensive alloy and leave the grain cut across the section. Open-die forging and ring rolling follow the shape of the part with the grain and give better soundness through the section. Jiangyin Jiangnan Metal Co., Ltd. forges FeNi48 close to finished shape from ESR remelted ingot.

02Thermal expansion: where FeNi48 sits

FeNi48 is a matched-expansion alloy rather than a low-expansion alloy. Its coefficient sits close to that of soda-lime glass, not close to zero.

A soda-lime glass seal made with 304 stainless steel would fail on the first thermal cycle. Made with Invar 36, the glass would be left in tension. FeNi48 is within about 0.5 µm/m·°C of the glass, which is close enough for a hermetic seal to survive repeated cycling.

Comparison values are nominal literature figures given for orientation. FeNi48 figures for Jiangyin Jiangnan Metal material are given in section 5 and are confirmed heat by heat on the mill certificate.

03Designations, standards and equivalent grades

FeNi48 is sold under at least eight names. All refer to the same nominal 48 % Ni, balance Fe composition.

Nilo® is a registered trademark of Special Metals Corporation. Invar® and Pernifer® are trademarks of their respective owners. Jiangyin Jiangnan Metal Co., Ltd. supplies to the equivalent chemistry and property requirements and is not affiliated with those trademark holders. Where a drawing calls out a proprietary name, quote that name on the enquiry and the material will be certified to the corresponding UNS or DIN designation.

04FeNi48 chemical composition

Nominal chemistry of FeNi48 (Alloy 48, UNS K94800), weight per cent.

Carbon, chromium and other residuals are held low because the surface oxide controls how molten glass wets and bonds to the metal. Jiangyin Jiangnan Metal melts FeNi48 by EAF plus VOD, followed by ESR remelting, to keep gas content and inclusion levels down before forging.

05Mechanical, physical and thermal properties

Typical room-temperature properties in the annealed condition. FeNi48 is supplied and used annealed, because cold work left in the material changes the expansion coefficient.

Values are typical and are given for design screening. Every FeNi48 forging shipped by Jiangyin Jiangnan Metal Co., Ltd. carries heat-specific test results on an EN 10204 3.1 or 3.2 certificate. Request the certificate before finalising a seal or thermostat design.

06FeNi48 forged product range and size envelope

Jiangyin Jiangnan Metal Co., Ltd. produces FeNi48 as open-die forgings and seamless rolled rings, forged to customer drawing or to a machining allowance you specify.

Delivery condition: forged, annealed, rough machined or finish machined. Descaled, pickled, turned, peeled or ground as required. State the machining allowance you want left on each surface and the part will be forged to that envelope.

07How FeNi48 forgings are produced

Five controlled stages from ingot to certified forging.

1. Melting. Electric arc furnace with vacuum oxygen decarburisation lowers carbon and gas content. Electroslag remelting then refines the ingot structure and reduces inclusion levels.
2. Hot forging. The ingot is soaked and forged in the region of 1,150 to 1,200 °C, finishing above roughly 900 °C. Enough reduction is applied to break down the as-cast structure and orient the grain flow along the part.
3. Ring rolling. For annular parts a pierced blank is rolled to final OD and ID, which produces circumferential grain flow that a machined ring cannot match.
4. Annealing. 850 to 1,000 °C (1,560 to 1,830 °F) in a protective atmosphere, followed by controlled cooling. Cold work left in the material changes the expansion coefficient, so FeNi48 is delivered annealed.
5. Testing and certification. Chemistry, mechanical test, ultrasonic examination and dimensional check, issued on an EN 10204 3.1 or 3.2 certificate.

Machining and welding notes

• FeNi48 work-hardens and produces a stringy chip. Use sharp positive rake tooling, rigid setups, generous coolant and lower cutting speeds than for carbon steel.
• On precision parts, add a stress-relief or re-anneal step before final machining. The expansion behaviour applies to material in the annealed condition.
• The alloy is readily fusion welded. Use matching Ni-Fe filler and keep the joint clean. Avoid heavy heat input local to a seal face.
• Surfaces that will be sealed to glass are normally supplied with a controlled oxide, or left for your own oxidising treatment. State which on the enquiry.

08Testing, NDT and certification

Every FeNi48 forging leaves the factory with traceable, heat-specific documentation.

If your drawing calls for a witness point, a specific UT acceptance class, or a customer-nominated inspector, state it at enquiry stage so the inspection plan is quoted correctly.

09Where FeNi48 forgings are used

Typical applications for FeNi48 forgings, listed by area.

Glass-to-metal and hermetic sealing

• Seals into soft lead and soda-lime glasses, the original and principal use of the alloy
• Microelectronic component packages, vacuum devices, electric lamp components
• Feedthroughs, sealed housings, forged flanges and tube sheets for sealed assemblies
• Semiconductor lead frames and related tooling

Dimensional stability and precision tooling

• Aerospace composite lay-up and cure tooling where the mould must track the part
• Dimensionally stable instrument frames and optical device mounts
• Metrology fixtures, positioning devices, precision spindles
• Cryogenic and LNG hardware, including containment components and transfer line parts

Thermal control and electromagnetic hardware

• Industrial thermostats and thermostat rods to 450 °C (840 °F)
• Bimetal thermostat strip components and bimetallic assemblies
• Electrical circuit breakers and temperature regulators
• Small transformer cores, magnetic shielding, cavity resonators and filters
• Clock balance wheels and pendulum components

Forged parts ordered against these applications include rings, seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings, tube sheets, valve bodies and seat rings, spindles, nozzles and near-net blanks. See also our forged rolls, forged tube sheets and forged valve seat rings pages.

10FeNi48 compared with Invar 36, Alloy 42 and Kovar

Controlled-expansion alloys are selected by matching the coefficient of the alloy to the material it is joined to.

Selection summary: for soda-lime or soft lead glass use FeNi48. For borosilicate glass or alumina ceramic use Kovar. For hard glass and semiconductor lead frames use Alloy 42. Where no movement is acceptable use Invar 36. If you state the glass or ceramic grade on the enquiry, the matching alloy can be confirmed before quotation.

11FeNi48 supplier information

FeNi48 open-die forgings and seamless rolled rings are produced by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No. 1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province 214423, China.

Jiangyin is in southern Jiangsu on the Yangtze River, with road access to the ports of Shanghai and Ningbo. The factory works to customer drawing across carbon steel, alloy steel, tool steel, stainless steel and nickel alloys. Controlled-expansion nickel-iron grades, including FeNi48, Invar 36 and Invar 42, are forged as a regular product line.

Scope of supply

• FeNi48 forged to drawing: rings, seamless rolled rings, flanges, bars, discs, shafts, sleeves, bushings, tube sheets and near-net blanks
• ESR remelted FeNi48 stock, with the melt route controlled from EAF and VOD through to ESR
• Annealing in a protective atmosphere at 850 to 1,000 °C
• Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, with EN 10204 3.1 or 3.2 certificates
• Rough machined and finish machined parts as well as black forgings
• Quotation from a drawing, a dimensioned sketch, or a written size and quantity

12FeNi48 frequently asked questions