Controlled-expansion alloy · UNS K94100 · W.Nr. 1.3917

FeNi42 Forgings

Q: What is the inflection point of FeNi42 and why does it matter?

The inflection point of FeNi42 is approximately 370 degrees Celsius. Below it the coefficient of thermal expansion stays low and nominally constant. Above it the expansion rate rises quickly and the alloy no longer tracks the glass, ceramic or silicon it was selected to match. Any design that depends on matched expansion has to keep the joint below about 370 degrees Celsius in service, even though the alloy itself is not damaged at higher temperatures.

Rings, bars, discs, flanges, shafts and sealing components, forged to your drawing

FeNi42 is an iron-nickel controlled-expansion alloy with a nominal 41 to 42 % nickel content and iron as the balance. It is designated UNS K94100 and Werkstoff number 1.3917. The alloy has a low, nominally constant coefficient of thermal expansion from room temperature up to about 300 °C. That figure is matched to silicon, alumina, beryllia and the common sealing glasses, so a metal part and a glass or ceramic part can expand and contract together without cracking the joint between them.

Jiangyin Jiangnan Metal Co., Ltd. forges FeNi42 to order at its works in Jiangyin, Jiangsu Province, China, and ships worldwide in the annealed condition with EN 10204 3.1 or 3.2 material certificates and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388.

DINFeNi42 / Ni42
UNSK94100
W.Nr.1.3917
ASTMF30 / F29 / B753
AFNORNF A54-301
GB4J42

Expansion map: where FeNi42 works, and where it stops working

20 °C
68 °F

300 °C
572 °F

370 °CInflection point
698 °F

600 °C
1112 °F

850-1000 °CAnneal
1560-1830 °F

The inflection point governs the design. Below about 370 °C the coefficient of expansion stays low and nominally constant, and the alloy tracks the glass, ceramic or silicon it was selected to match. Above 370 °C the expansion rate rises quickly and the match is lost. The alloy itself is not damaged, but the seal will not hold. FeNi42 also has to be delivered annealed at 850-1000 °C in a protective atmosphere, since residual cold work changes the expansion coefficient. We supply annealed unless the order states otherwise.

Grade

What is FeNi42 used for?

FeNi42 is specified when a metal part has to stay dimensionally in step with a glass, ceramic or silicon component across a temperature swing. Common duties are glass-to-metal and ceramic-to-metal seals, semiconductor lead frames, hermetic packages, thermostat rods, bi-metal thermostat strip and tooling for aerospace composites.

The alloy sits in the invar region of the iron-nickel system, where the face-centred cubic lattice changes size very little on heating. Raising the nickel content to 41 or 42 % lifts the expansion figure above the Invar 36 minimum, up to a value that tracks silicon, alumina and the common sealing glasses. The alloy is therefore selected for a matched expansion figure rather than for the lowest one available.

Two consequences follow, and both of them turn up on drawings. The joint has to stay below the inflection point at roughly 370 °C, or the match is lost. The material also has to be annealed, because residual cold work from forming or machining distorts the expansion curve. This is why FeNi42 is bought, forged and delivered annealed rather than work-hardened for strength.

Cross-reference

FeNi42 equivalents and specifications

These designations all describe the same 42 % nickel iron-nickel controlled-expansion alloy. If your drawing calls out any one of them, we can quote it.

DIN designation: FeNi42 / Ni42 / NiFe42
Werkstoff number: 1.3917
UNS number: K94100
Sheet, strip, rod, bar, tube, wire: ASTM F30
Wire: ASTM F29
Sheet and strip: ASTM B753
German standards: DIN 17745, SEW 385
French standard: AFNOR NF A54-301
Chinese grade: 4J42
Trade names: Nilo^® 42, Pernifer^® 42, Dilaton 42, Invar 42, Glass Sealing 42, Alloy 42

Nilo^® is a registered trademark of Special Metals Corporation and Pernifer^® of VDM Metals. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with, endorsed by or licensed by those owners. The names are used here only to identify equivalent alloy designations.

Chemistry

Chemical composition of FeNi42

Composition in weight percent, with iron as the balance element:

FeNi42 (UNS K94100) chemical composition, wt %
Element	Symbol	Composition
Iron	Fe	Balance
Nickel, nominal	Ni	41
Cobalt, nominal	Co	None
Carbon	C	0.05 max
Silicon	Si	0.30 max
Sulfur	S	0.025 max
Chromium	Cr	0.025 max

Figures are maximum unless noted otherwise. Manganese, phosphorus and residual elements are controlled to the applicable standard and reported on the heat certificate. The ladle analysis on your EN 10204 certificate governs. Send us your specification if you need a tightened range on any element, particularly where the expansion coefficient is closely toleranced.

Mechanical

Mechanical properties of FeNi42

Typical room-temperature data in the annealed condition, given in both imperial and SI units:

FeNi42 typical mechanical properties, annealed
Property	Imperial	SI
Tensile strength	82 ksi	566 MPa
Yield strength	34 ksi	235 MPa
Elongation in 2 in. / 50.8 mm	30 %	30 %
Hardness, annealed	80 HRB	80 HRB

Typical values for annealed material, published for guidance only. They are not guaranteed minima and they are not a substitute for the tensile results on your mill certificate. Section size, reduction ratio and test orientation all affect results on a heavy forging. Tell us your acceptance criteria and test position at enquiry stage and we will confirm what we can meet before you place the order.

Strength is rarely the governing property

FeNi42 is not a high-strength alloy and is not bought as one. At 235 MPa yield it is comparable to a soft austenitic stainless steel. Almost every FeNi42 drawing is governed by expansion behaviour and dimensional stability instead, which is why the annealed condition is specified even though cold work would raise strength considerably. If your part needs controlled expansion together with higher strength, tell us at enquiry stage. NI-SPAN-C Alloy 902 is sometimes the better answer.

Thermal

Expansion and physical properties of FeNi42

This is the data the alloy is actually selected on. The expansion figure is a mean value across the stated range, not a point value:

FeNi42 typical physical and thermal properties
Property	Typical value	Notes
Mean coefficient of expansion	4.3-5.3 × 10⁻⁶/°C	Over 20-300 °C, annealed
Inflection point	approx. 370 °C	Expansion rate rises above this temperature
Density	approx. 8.12 g/cm³	0.293 lb/in³
Melting range	approx. 1430 °C	Approximately 2600 °F
Annealing	850-1000 °C	1560-1830 °F, protective atmosphere, time to section
Delivery condition	Annealed	Cold work distorts the expansion coefficient

Physical property values are indicative and drawn from published data for the Alloy 42 and UNS K94100 family. Where your design depends on a tight expansion match, request certified expansion data for the specific heat at order stage rather than working from these figures.

Selection

FeNi42 or Invar 36?

These two grades arrive on enquiries interchangeably, and they are not interchangeable. Invar 36 is chosen for the least possible movement. FeNi42 is chosen to match the movement of something else.

FeNi42 compared with Invar 36
	FeNi42 (Alloy 42)	Invar 36
Nominal nickel	41-42 %	36 %
UNS number	K94100	K93600 / K93601
Werkstoff number	1.3917	1.3912
Expansion, 20-300 °C	4.3-5.3 × 10⁻⁶/°C	1.2-2.0 × 10⁻⁶/°C
Design intent	Match silicon, alumina, sealing glass	Minimum dimensional movement
Typical duty	Lead frames, glass-to-metal seals, hermetic packages, thermostat rods	LNG containment, metrology, composite tooling, precision instruments
Forged by us	Yes, this page	Yes, Invar 36 forgings

If the part seals against a glass or ceramic, name that material when you enquire. The seal only holds if the two expansion curves track each other across the full operating range, and that occasionally points to Alloy 48 or Invar 42 rather than FeNi42.

Process

How we make a FeNi42 forging

The order the steps run in matters, because the alloy loses the expansion behaviour it is bought for if it is left in the worked condition.

Melting. EAF followed by VOD refining, then ESR remelt. The electroslag step controls sulfur and non-metallic inclusions, and that cleanliness is what makes the expansion coefficient repeatable from heat to heat.
Heating and open-die forging. The billet is upset and drawn on the press to break down the cast structure and work the whole cross-section rather than just the skin. Rings are punched and expanded on the ring rolling mill to give continuous circumferential grain flow.
Annealing. 850 to 1000 °C (1560 to 1830 °F) in a protective atmosphere, held to section thickness. This restores the low, constant expansion coefficient after hot work.
Rough machining. Scale removal and stock allowance turned to your drawing, or finish machining to print. Where dimensional stability is critical, a stress-relief cycle is run between rough and finish machining.
Non-destructive testing. Ultrasonic testing to the acceptance class you nominate, plus PT where specified.
Documentation and despatch. EN 10204 3.1 or 3.2 certificate, heat number traceability, marking, preservation and export packing.

Product forms

FeNi42 forged shapes and sizes

Everything below is made to drawing or to a size list. There is no fixed catalogue, because open-die forging is a one-off process. If the shape can be forged, it can be quoted.

Rings & rolled rings Seamless rolled rings, seal rings, retaining rings, spacer rings.
Bars, shafts & spindles Round, square and flat bar; thermostat rods; stepped and eccentric shafts.
Discs & blanks Solid discs, gear blanks, balance-wheel blanks, cover plates.
Flanges & tube sheets Weld-neck and blind flange forgings, tube sheets, sealing frames.
Sleeves & hollow bar Bushings, liners, forged tubes, bored and trepanned hollows.
Valve & housing parts Bodies, seat rings, stems, nozzles, manifolds, electronic housings.

Sizes we forge

Indicative open-die forging range, confirm your part at enquiry
Form	Dimension range	Single-piece weight
Rolled rings	OD 200-3000 mm, wall from 30 mm, height to 800 mm	up to 8000 kg
Round bars & shafts	Ø 60-800 mm, length to 6000 mm	up to 8000 kg
Discs & blanks	Ø 150-2000 mm, thickness 30-600 mm	up to 8000 kg
Sleeves & hollows	OD to 1500 mm, ID from 100 mm	up to 8000 kg
Blocks & shaped parts	To drawing	up to 8000 kg

Ranges are indicative for the open-die process. Controlled-expansion alloys are ordered in small quantities far more often than in tonnage lots, so single-piece and prototype orders are normal. Please ask.

Quality

Testing, certificates and traceability

What ships with the forging is part of the order. Specify the level you need and it is quoted in.

Material certificates

EN 10204 3.1. Issued by our own quality department, independent of production.
EN 10204 3.2. Witnessed and countersigned by a third party such as TÜV, SGS, BV, DNV or Lloyd's Register, or by your own inspector.

Non-destructive testing

Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Name the quality class and the acceptance level with your enquiry.
Liquid penetrant (PT) where the drawing calls for surface examination. FeNi42 is ferromagnetic below its inflection point, so magnetic particle inspection is also possible, but PT is normally specified for sealing surfaces because it leaves no residual magnetism.

Included in the documentation package

Heat number and full melt-to-part traceability
Chemical analysis (ladle and, on request, product analysis)
Tensile and hardness results at the specified test position
Heat treatment charts for the anneal
Certified thermal expansion data for the heat, on request
Dimensional inspection report
NDT reports, marking record and packing list

Applications

Where FeNi42 forgings are used

Grouped by the industry that buys them, with the parts we are most often asked to forge:

Semiconductor & microelectronicsBars, discs and rings for lead frames, semiconductor packages, hermetic housings, and echo boxes and filters for mobile telephones.
Glass & ceramic sealingRings, flanges, sleeves and tube sheets for glass-to-metal and ceramic-to-metal seals, electronic tubes, CRT electron guns, vacuum devices, electric lamp bulbs and specialty hermetic packages.
Aerospace compositesSeamless rolled rings and forged shafts for advanced composite moulds and layup tooling, where the tool must not drift relative to the part during cure.
Thermostats & temperature controlBars and rods for thermostat rods, thermostatic bi-metal strip, bimetal thermostats, temperature regulators and electrical circuit breakers.
Cryogenic & LNGOpen-die forgings, nozzles and forged crankshafts for LNG tanker containment and transfer line hardware requiring dimensional stability.
Precision instruments & metrologyForged wheels, spindles and gear blanks for scientific instruments, positioning devices, clock balance wheels, pendulum clocks and metrology equipment.
RF, radar & powerForged blanks, nozzles and eccentric shafts for radar and microwave cavity resonators, magnetic shielding, small electrical transformers and precision condenser blades.
Valves & flow controlBodies, stems, seat rings and blocks for ball, gate, globe, check and plug valves and strainers where thermal cycling governs seat clearance.

Downstream

Machining and welding FeNi42

Machining

FeNi42 machines much like a soft austenitic stainless steel. It is gummy rather than abrasive, so the failure mode is built-up edge and a torn finish rather than rapid flank wear.

Sharp, positive-rake tooling. A keen edge matters more than a hard grade.
Moderate surface speed with a generous, constant feed. Do not let the tool dwell and rub.
Rigid setup and short overhang. Chatter tears the surface on a gummy material.
Flood coolant, well directed, to clear the chip and stop it welding to the edge.
Where the finished part must hold size, stress-relieve between rough and finish machining.

We can supply the forgings rough machined or fully finish machined to your drawing if this is not work your shop wants to take on.

Welding

FeNi42 is readily weldable by GTAW (TIG), GMAW (MIG) and resistance methods with matching filler, and it is routinely brazed and glass-sealed. The point to watch is not weldability but expansion. The heat-affected zone and any cold work around it will not share the parent metal expansion curve until the part is re-annealed. Where the joint has to hold a matched seal, re-anneal after welding.

Questions

FeNi42: frequently asked questions

What is FeNi42?

FeNi42 is an iron-nickel controlled-expansion alloy with a nominal 41 to 42 % nickel content and iron as the balance. It is designated UNS K94100 and Werkstoff number 1.3917, and it is also sold as Alloy 42, Ni42, NiFe42, Nilo 42, Pernifer 42, Dilaton 42, Invar 42, Glass Sealing 42 and the Chinese grade 4J42. The alloy has a low, nominally constant coefficient of thermal expansion from room temperature to about 300 °C, matched to silicon, alumina, beryllia and sealing glasses. That is why it is the standard material for glass-to-metal seals, semiconductor lead frames and hermetic electronic packages.

What is the equivalent of FeNi42 in UNS, ASTM and DIN?

FeNi42 corresponds to UNS K94100 and Werkstoff number 1.3917. Product standards covering the alloy include ASTM F30 for sheet, strip, rod, bar, tubing and wire, ASTM F29 for wire, ASTM B753, DIN 17745, SEW 385 and AFNOR NF A54-301. The Chinese grade is 4J42. Common trade and alternate names are Alloy 42, Ni42, NiFe42, Nilo^® 42, Pernifer^® 42, Dilaton 42, Invar 42 and Glass Sealing 42.

What is the difference between FeNi42 and Invar 36?

The difference is nickel content, and therefore expansion behaviour. Invar 36 contains about 36 % nickel and has the lowest thermal expansion in the iron-nickel family, roughly 1.2 to 2.0 × 10⁻⁶/°C. It suits LNG containment, metrology and large composite tooling. FeNi42 contains about 41 to 42 % nickel and expands more, roughly 4.3 to 5.3 × 10⁻⁶/°C, at a rate chosen to track silicon, alumina and sealing glasses.

Use Invar 36 where you want the least movement. Use FeNi42 where the part has to match the expansion of a mating glass, ceramic or silicon component. Jiangyin Jiangnan Metal Co., Ltd. forges both grades.

Why must FeNi42 be supplied in the annealed condition?

Residual cold work changes the coefficient of thermal expansion, which is the property the alloy is bought for. FeNi42 is therefore supplied and used annealed. Annealing is carried out between 850 °C and 1000 °C (1560 to 1830 °F) in a protective atmosphere, with holding time adjusted to section thickness. Where dimensional stability is critical, run a stress-relief cycle after rough machining and before finish machining.

What is the inflection point of FeNi42 and why does it matter?

The inflection point of FeNi42 is approximately 370 °C. Below it the coefficient of thermal expansion stays low and nominally constant. Above it the expansion rate rises quickly and the alloy no longer tracks the glass, ceramic or silicon it was selected to match.

Any design that depends on matched expansion has to keep the joint below about 370 °C in service, even though the alloy itself is not damaged at higher temperatures. This is the most common reason an FeNi42 seal fails in an application that looked correct on paper.

What forged shapes are available in FeNi42?

Jiangyin Jiangnan Metal Co., Ltd. produces FeNi42 as open-die forgings and seamless rolled rings, including forged rings, rolled rings, round and flat bars, shafts, spindles, eccentric shafts, discs and blanks, flanges, tube sheets, forged tubes, sleeves, bushings, hollow bars, nozzles, gear blanks, wheels, rolls, manifolds and valve bodies, seats and stems. Parts are made to the customer drawing or size list rather than from a fixed catalogue.

Can FeNi42 be machined and welded?

Yes to both. FeNi42 machines much like an austenitic stainless steel. It is gummy and tends to build up on the cutting edge, so sharp positive-rake tooling, moderate surface speed, constant feed and flood coolant give the best result. It is readily weldable by GTAW, GMAW and resistance methods with matching filler.

Both operations affect expansion behaviour, so re-anneal after significant hot or cold work where matched expansion is critical. Jiangyin Jiangnan Metal can supply forgings rough machined or finish machined.

What certificates and testing come with FeNi42 forgings?

Every FeNi42 forging from Jiangyin Jiangnan Metal ships with a material certificate to EN 10204 3.1, or 3.2 with third-party witness such as TÜV, SGS, BV, DNV or Lloyd's Register. Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 as specified. The documentation package covers chemical analysis, mechanical test results, heat treatment records and dimensional inspection. Certified thermal expansion data for the heat can be supplied on request.

Who supplies FeNi42 forgings?

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory that supplies FeNi42 (Alloy 42, UNS K94100) forgings worldwide. The works is at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Quotations are issued from a drawing or a size list. Contact sales@steelforgepieces.com or +86 189 2135 9659.

What information is needed to quote a FeNi42 forging?

Send the drawing or rough dimensions, the quantity, the delivery condition required (as-forged, rough machined or finish machined), the certificate level (EN 10204 3.1 or 3.2), any NDT requirement and acceptance class, and the destination port.

If the part seals against a glass or ceramic, name that material as well, because it decides whether FeNi42 or a neighbouring grade is the right choice. Jiangyin Jiangnan Metal normally returns a price and lead time within 24 hours on working days.

The supplier

Who forges FeNi42

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin City, Jiangsu Province, China, producing forged rings, seamless rolled rings, bars, discs, flanges, shafts, sleeves and valve components in carbon steel, alloy steel, tool steel, stainless steel, nickel alloys and controlled-expansion alloys including FeNi42 (Alloy 42 / UNS K94100 / W.Nr. 1.3917).

Work is made to the customer drawing rather than from a stock list, delivered in the annealed condition, with EN 10204 3.1 or 3.2 material certificates and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. Forgings are exported worldwide, and single-piece and prototype orders are accepted, which is how most controlled-expansion parts are bought.

The works is at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. To reach the sales desk directly, email sales@steelforgepieces.com or call +86 189 2135 9659.

Company: Jiangyin Jiangnan Metal Co., Ltd.
Business: Open-die forging factory & ring rolling
Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone: +86 189 2135 9659
Email: sales@steelforgepieces.com
Website: steelforgepieces.com
Certificates: EN 10204 3.1 / 3.2
Export markets: Worldwide

Send us the drawing. We will quote it.

Price and lead time normally come back within 24 hours on working days. Rough dimensions are enough to start. A finished drawing is not required for a budget figure.

Email sales@steelforgepieces.com Call +86 189 2135 9659

Drawing or dimensions
Quantity
Delivery condition
Certificate level
NDT & acceptance class
Mating glass or ceramic
Destination port