Controlled Expansion Alloys · Iron-Nickel · UNS Register

UNS K94100 Forging Parts Alloy 42 · ASTM F30 · DIN 1.3917 · NiFe42

UNS number

K94100

Common name

Alloy 42

Specification

ASTM F30

Werkstoff

1.3917 NiFe42

France

NF A54-301

Trade names

Nilo® 42 Pernifer® 40

Published: 12 May 2022 · Last updated: 28 August 2026 · Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

UNS

K94100

Nickel

41wt %

CTE 20–100 °C

5.3×10⁻⁶ /°C

Density

8.11g/cm³

Inflection pt

370°C

Melting pt

1435°C

Max ring OD

2500mm

Max piece

8000kg

What is UNS K94100?

UNS K94100 is a binary iron-nickel alloy of nominally 41% nickel and balance iron, registered in the Unified Numbering System and specified for one reason: its coefficient of thermal expansion is low, predictable, and close to that of the materials it is sealed or bonded to. In everyday industry usage it is called Alloy 42. It belongs to the controlled-expansion family that begins with Invar 36 (UNS K93600) and runs upward through K94100, K94600, K94800 and N14052 as nickel content increases.

What produces this behaviour is the Invar effect. In face-centred-cubic iron-nickel alloys near 36% nickel, normal thermal expansion of the crystal lattice is almost cancelled by a magnetostrictive contraction that occurs as ferromagnetic ordering weakens with rising temperature. The cancellation is strongest at 36% Ni, and adding nickel reduces it in a controlled, repeatable way. At 41–42% Ni the residual expansion settles at roughly 5.3 ppm/°C, which is close to the values for silicon, alumina and several hard sealing glasses. The nickel level in this grade is chosen for that match rather than for minimum expansion.

Two consequences follow from this mechanism, and between them they account for most field problems with the grade.

• The low expansion disappears above the inflection point (~370 °C). The magnetostrictive contraction that produces the effect stops once the alloy passes its Curie temperature and becomes paramagnetic. Above that point the expansion coefficient climbs toward that of an ordinary austenitic alloy. The useful controlled-expansion range of UNS K94100 is therefore quoted as room temperature to about 300 °C, and assuming the low CTE holds at 500 °C is a design error.
• Cold work distorts the expansion curve. Residual strain from drawing, straightening or heavy machining shifts the measured coefficient away from the datasheet value. The grade is supplied and used in the annealed condition for this reason, and precision parts usually receive a stabilising treatment after final machining.

There is essentially no chromium in the alloy, so it has only modest oxidation resistance and little corrosion resistance. Where a controlled-expansion part also has to survive an aggressive environment, the usual answer is protective plating (nickel or gold on lead frames) or a change of grade.

How the UNS designation is built

The Unified Numbering System is maintained jointly by SAE International and ASTM International and published as ASTM E527 / SAE J1086. Each entry is a single letter followed by five digits. The letter identifies the family, and the digits locate the alloy within it.

That last row is the point that matters commercially, and it is the subject of the next section.

UNS K94100 forgings: supplier quick facts

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, producing UNS K94100 (Alloy 42 / ASTM F30 / DIN 1.3917) forged rings, seamless rolled rings, flanges, shafts, discs, sleeves, bushings, tube sheets and bars to customer drawings.

What Does UNS K94100 Actually Specify, and What Does It Not?

A UNS number identifies a chemical composition and nothing else. It is not a specification, not a standard, and not a purchasing document. K94100 fixes the nominal 41% nickel iron-base chemistry and the residual limits. It says nothing about the form the metal arrives in, the condition it is in, how strong it is, how it was tested, or what paperwork comes with it.

This trips up more orders on this grade than any metallurgical issue, because the expansion coefficient, which is the property customers are actually buying, is not guaranteed by the chemistry alone. Two heats that both conform to K94100 can measure differently, and a cold-worked bar and an annealed bar from the same heat will certainly measure differently.

What Are the Equivalent Designations of UNS K94100?

Engineers arrive at this grade through at least a dozen different names, depending on which standards body, which producer and which decade the drawing came from. Every designation in the table below refers to the same nominal Fe-42Ni controlled-expansion chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under all of them, supplying material certified to UNS K94100 / ASTM F30 with the equivalents cross-listed on the certificate.

What Is the Chemical Composition of UNS K94100?

The composition below reflects ASTM F30 practice for the 42% nickel sealing alloy. The chemistry is simple by design: nickel sets the expansion coefficient, and every other element is held low because residuals shift the expansion curve, degrade the magnetic behaviour or interfere with glass wetting during sealing. Carbon is capped tightly because it embrittles the alloy and forms carbides that disturb the expansion match.

Our melting practice. Jiangyin Jiangnan Metal Co., Ltd. melts UNS K94100 by EAF + VOD followed by ESR (electroslag remelting). VOD reduces carbon and dissolved gases. ESR refines the inclusion population and gives the directional solidification structure that produces a clean, uniform forging. For sealing and lead-frame applications where surface oxide quality governs adhesion, we can also source VIM + VAR double-vacuum stock. Specify this at RFQ stage, since it changes both price and lead time. The full ladle analysis and the product analysis are both reported on the EN 10204 certificate.

What Is the Coefficient of Thermal Expansion of UNS K94100?

The mean coefficient of thermal expansion of UNS K94100 is approximately 5.3 × 10⁻⁶ /°C over 20–100 °C, and falls in the range 4.5–6.5 × 10⁻⁶ /°C over 20–300 °C (about 2.9 × 10⁻⁶ /°F over 70–212 °F, and 2.5–3.6 × 10⁻⁶ /°F over 70–572 °F). This is the number the alloy is bought for, and it is the number to verify on the certificate.

Three practical points follow from this.

1. Mean versus instantaneous. Datasheet values are mean coefficients between room temperature and the stated upper temperature. If a part cycles between 150 °C and 250 °C, the mean coefficient over that interval is not the 20–300 °C figure. For tight seals, request the measured expansion curve rather than a single number.
2. Heat-to-heat variation is significant. A 0.5% shift in nickel moves the coefficient measurably. For precision work, order all parts of an assembly from a single heat and state that requirement on the purchase order. We will reserve material accordingly.
3. Condition governs the value. A cold-drawn or heavily machined part will not measure at the annealed value. Anneal, then finish, then stabilise.

For an interactive expansion calculator and a glass and ceramic seal-match checker built on these figures, see the companion Alloy 42 datasheet.

What Are the Physical Properties of UNS K94100?

Data notes. Density, melting point, inflection point and the 20–100 °C expansion coefficient are well established for this chemistry and can be used directly. The values marked "typical" (specific heat, resistivity, modulus and Poisson's ratio) vary with heat, section size and condition, and should be treated as indicative for screening only. Where any physical value is contractually important, state it on the purchase order and Jiangyin Jiangnan Metal Co., Ltd. will report the measured result on the material certificate.

What Are the Mechanical Properties of UNS K94100?

UNS K94100 is not a structural alloy. It is austenitic, cannot be hardened by heat treatment, and is used at modest stress levels. The mechanical properties matter mainly for handling, machining and forming rather than for load capacity. Strength can only be raised by cold work, and cold work is what destroys the expansion accuracy, so in practice the annealed properties are the ones that apply to a finished forged part.

Where the grade is ordered as strip or flat product rather than as a forging, ASTM F30 and thermostat-metal practice describe it by temper rather than by a single annealed value. Those tempers are produced by cold rolling, so each step up in strength moves the expansion coefficient further from the annealed figure.

How Is UNS K94100 Annealed and Heat Treated?

UNS K94100 has no hardening transformation. The only heat treatments that matter are the ones that remove cold work and stabilise dimensions, and both exist to protect the expansion coefficient.

Processing sequence matters on precision parts. The correct order is: forge, anneal, rough machine, intermediate stress relief, finish machine, stabilise at 300–350 °C, then measure. Skipping the intermediate relief on a part with heavy stock removal lets residual stress redistribute after finishing, and the part moves. On a 500 mm ring the movement is typically tens of microns, which is enough to fail a metrology or sealing application.

UNS K94100 vs K93600, K94600, K94800, N14052 and K94610

The controlled-expansion family is chosen by expansion coefficient, not by strength or corrosion resistance. The table below is the practical selection chart: find the CTE you need to match, and the UNS number follows.

K94100 against K94610 (Kovar) is the comparison that comes up most often

Their room-temperature coefficients are almost identical, so the two are often assumed to be interchangeable. They are not. The 17% cobalt in K94610 holds the expansion curve flat and matched to borosilicate glass up to about 450 °C, whereas K94100 starts to diverge above its 370 °C inflection point. Where a seal is made at or cycles near 450 °C, the cost premium for Kovar is justified. Below 300 °C, which covers lead frames, thermostats, positioning hardware and most alumina seals, K94100 does the same job without cobalt in the bill of materials.

K94100 against K93600 (Invar 36)

Both are binary nickel-iron controlled-expansion alloys, but the nickel content sets the expansion. K93600 contains about 36% nickel and has the lowest expansion of the family at roughly 1.3 ppm/°C over 20–100 °C, which makes it the choice for dimensionally stable instruments, LNG containment and aerospace composite tooling. K94100 contains about 41% nickel and expands at roughly 5.3 ppm/°C, which deliberately matches silicon, alumina and hard sealing glasses. K93600 is specified where the least possible movement is wanted; K94100 is specified where the expansion has to match a particular glass, ceramic or semiconductor. See our Invar 36 forgings page for that grade.

What Forged Products Are Available in UNS K94100?

Jiangyin Jiangnan Metal produces UNS K94100 through three routes, selected by geometry and quantity. Open-die forging covers long shafts, blocks, tube sheets and large discs, and is used wherever single-piece size matters more than repeatability. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter and is the normal choice for sealing rings, flange blanks, positioning rings and instrument frames. Near-net-shape forging is used where the die profile can remove 30–50% of the rough machining. That saving is worth more on this grade than on most, because the alloy is expensive per kilogram and slow to machine.

One route-selection point applies specifically to this grade. Since UNS K94100 is bought for dimensional behaviour, grain flow and residual stress matter more than peak strength. A rolled ring with continuous circumferential grain flow holds its diameter through thermal cycling better than the same ring machined out of plate, even though both meet the same ASTM F30 chemistry. For precision frames and rings, specify the forged route rather than accepting a machined-from-solid substitute.

• Seamless rolled rings
• Forged rings
• Forged flanges
• Forged round bars
• Forged flat bars & blocks
• Forged discs & blanks
• Forged shafts & spindles
• Forged sleeves & bushings
• Forged tube sheets
• Forged tubes & hollows
• Forged gear blanks
• Custom near-net-shape parts

Where Is UNS K94100 Used?

All of the applications below rely on the same property: the alloy moves by a small, known and repeatable amount when temperature changes.

UNS K94100 Production Capability at Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. operates an open-die forging and ring-rolling plant in Jiangyin, Jiangsu Province, China, employing approximately 460 people including 9 senior engineers and 32 intermediate engineers. UNS K94100 is produced alongside the rest of our controlled-expansion range (Invar 36, Invar 42 and Alloy 48) on the same equipment used for nickel alloys and precipitation-hardening stainless grades.

Standards, Testing and Certification

UNS K94100 orders at Jiangyin Jiangnan Metal Co., Ltd. are produced and certified against the specifications below. The chemistry specification is normally ASTM F30 or DIN 1.3917; the inspection-document type is normally EN 10204 3.1.

• UNS K94100
• ASTM F30
• ASTM F29
• ASTM B753
• AMS 23011 Cl.5
• DIN 1.3917 / NiFe42
• DIN 17745
• SEW 385
• AFNOR NF A54-301
• GB/T 4J42
• EN 10204 3.1
• EN 10204 3.2
• EN 10228-3 (UT)
• SEP 1921 (UT)
• ASTM A388 (UT)
• ISO 9001:2015

What appears on the certificate

• Heat number and full ladle plus product chemical analysis
• Melting route (EAF + VOD + ESR, or VIM + VAR where specified)
• Mechanical test results (tensile, yield, elongation, hardness) on coupons from the delivered heat
• Heat-treatment records: anneal temperature, hold time, atmosphere, cooling method; stabilising cycle where applied
• Ultrasonic examination report to the ordered standard and acceptance class
• Dimensional inspection report
• Measured coefficient of thermal expansion over the ordered temperature range, added on request and strongly recommended for sealing and metrology parts
• Cross-listed equivalent designations (UNS K94100 / ASTM F30 / DIN 1.3917 / NiFe42 / NF A54-301)

Quality gates and non-conformance handling

Every UNS K94100 order passes six mandatory hold points at which production cannot continue without QA sign-off: raw-material chemistry verification, forging temperature compliance, post-forging ultrasonic examination, heat-treatment chart approval, mechanical and expansion test acceptance, and final NDE plus dimensional inspection. Customer-witnessed hold points can be added at no charge. Any out-of-specification finding raises a formal non-conformance report within 24 hours, with root-cause analysis inside five working days and the proposed disposition sent to the customer before any rework is carried out.

How to Specify a UNS K94100 Forging Order

UNS K94100 carries one specification decision that most grades do not. The expansion requirement has to be stated explicitly, because it is the property being bought and, as Table 3 shows, it is not implied by the UNS number or the chemistry alone. The steps below remove the ambiguity that causes most disputes on this grade.

Recommended drawing callout

Top 10 Mistakes When Ordering UNS K94100 Forgings

1. Treating the UNS number as a complete specification. K94100 fixes chemistry only. Form, condition, expansion, testing and certification all have to be added.
2. Assuming the low expansion holds at high temperature. Above the 370 °C inflection point the effect is gone. Design and qualify inside the useful range, or change grade.
3. Confusing "Invar 42" with Invar 36 (K93600). A four-fold difference in expansion coefficient. Always confirm against the required CTE value, never against the name on the drawing.
4. Treating K94100 and K94610 (Kovar) as interchangeable. Similar at room temperature, different above 370 °C, and different in cost by a factor of two and a half.
5. Ordering the chemistry but not the expansion coefficient. ASTM F30 chemistry alone does not guarantee a specific CTE. If it matters, specify it and require it on the certificate.
6. Accepting parts machined from plate in place of forgings. Grain flow and residual stress differ; the machined part will move more through thermal cycling.
7. Skipping the stabilising treatment after final machining. Residual stress redistributes in service and the part drifts out of tolerance, often weeks after acceptance.
8. Mixing heats within a single assembly. Small nickel differences between heats produce measurable expansion differences. Specify single heat.
9. Specifying high strength alongside tight expansion control. These conflict for this grade. Resolve the requirement, or move to a hardenable controlled-expansion alloy.
10. Leaving surface-oxide condition unspecified on sealing parts. Glass adhesion depends on the oxide the part arrives with. State the required surface condition and pre-oxidation treatment at RFQ stage.

Glossary

UNS

Unified Numbering System for Metals and Alloys, maintained jointly by SAE International and ASTM International and published as ASTM E527 / SAE J1086. A UNS number identifies a chemical composition; it is not itself a specification.

UNS K94100

The UNS designation for the controlled-expansion iron-nickel alloy of nominally 41% Ni, balance Fe. Known in industry as Alloy 42. The generic, brand-free name to use on purchase orders.

K prefix

The UNS family letter for miscellaneous steels and ferrous alloys, which is where the iron-nickel sealing and controlled-expansion alloys are registered.

ASTM F30

Standard Specification for Iron-Nickel Sealing Alloys, covering the composition and property requirements of UNS K94100 and its neighbours in sheet, strip, rod, bar, tube and wire.

CTE

Coefficient of thermal expansion. The fractional change in length per degree of temperature change, quoted here in units of 10⁻⁶ per °C, equivalently parts per million per °C (ppm/°C).

Mean CTE

The average coefficient between two stated temperatures, as distinct from the instantaneous coefficient at a single temperature. Datasheet figures are almost always mean values referenced to room temperature.

Invar effect

The anomalous near-cancellation of thermal expansion in face-centred-cubic Fe-Ni alloys near 36% nickel, caused by a magnetostrictive contraction offsetting normal lattice expansion.

Inflection point

The temperature at which the expansion curve bends sharply upward, coincident with the Curie point at about 370 °C for UNS K94100. The practical ceiling for controlled-expansion service.

Curie temperature

The temperature above which a ferromagnetic material becomes paramagnetic. In the Fe-Ni controlled-expansion alloys the Curie point and the expansion inflection point are the same physical event.

Matched seal

A glass- or ceramic-to-metal seal in which both materials have nearly identical expansion coefficients, so the joint cools to near-zero residual stress.

Compression seal

A seal designed so the metal contracts slightly more than the glass, leaving the glass in compression, which is the stress state glass tolerates best.

Lead frame

The stamped or etched metal frame that carries the electrical connections and mechanical support of a semiconductor package. UNS K94100 is one of the two dominant lead-frame materials, alongside copper alloys.

ESR

Electroslag remelting. A secondary melting process that refines inclusion content and produces a directionally solidified ingot suited to forging.

VOD

Vacuum oxygen decarburisation. A secondary refining step that lowers carbon and dissolved gases.

Stabilising treatment

A low-temperature soak, typically 300–350 °C, applied after final machining to relieve residual stress and lock dimensions before service.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is a mill certificate issued by the manufacturer's own independent inspection department; 3.2 is countersigned by an independent third party nominated by the purchaser.

Seamless rolled ring

A ring produced by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow and better dimensional stability than a ring machined from plate.

Single heat

A purchase-order requirement that all pieces come from one melt, so that small heat-to-heat nickel differences cannot produce differing expansion behaviour within one assembly.

Frequently Asked Questions: UNS K94100

Technical References

Chemistry, expansion, physical-property and heat-treatment data on this page are drawn from the published standards and engineering references below. Test results reported on our material certificates are independent and traceable to calibrated laboratory equipment.

1. ASTM E527 / SAE J1086, Standard Practice for Numbering Metals and Alloys in the Unified Numbering System (UNS), ASTM International and SAE International.
2. ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys, ASTM International, West Conshohocken, PA.
3. ASTM F29, Standard Specification for Dilute Nickel-Iron Sealing Alloys, ASTM International.
4. ASTM F15, Standard Specification for Iron-Nickel-Cobalt Sealing Alloy, ASTM International (Kovar / UNS K94610 comparison data).
5. ASTM F1684, Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications, ASTM International (Invar 36 / UNS K93600 comparison data).
6. ASTM B753, Standard Specification for Thermostat Component Alloys, ASTM International.
7. DIN 17745, Wrought alloys of nickel and iron, Deutsches Institut für Normung.
8. SEW 385, Stahl-Eisen-Werkstoffblatt, nickel-iron alloys, sheet, strip and bar, Verein Deutscher Eisenhüttenleute.
9. AFNOR NF A54-301, Nickel-iron controlled expansion alloys, Association Française de Normalisation.
10. EN 10204:2004, Metallic products. Types of inspection documents, CEN, Brussels.
11. EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN.
12. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
13. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
14. ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International, section on low-expansion alloys.
15. ASM Specialty Handbook: Nickel, Cobalt and Their Alloys, J.R. Davis (ed.), ASM International.
16. Guillaume, C.É., Recherches sur les aciers au nickel, the original work on the Invar effect, Comptes Rendus de l'Académie des Sciences, 1897 (Nobel Prize in Physics, 1920).
17. Wachtel, E. and Bakonyi, I., Magnetism and thermal expansion anomalies in Fe-Ni alloys, standard reference literature on the Invar mechanism.
18. Espe, W., Materials of High Vacuum Technology, Pergamon Press. Glass-to-metal and ceramic-to-metal sealing practice.

Standards cited are the revisions known to us at the time of the last page review. For procurement, always reference the revision in force at the contract date. All trademarks referenced belong to their respective owners.

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Related Grades and Forged Products

• Alloy 42 datasheet
• Invar 36 / K93600
• Invar 42
• Alloy 48 / K94800
• Ni-Span-C Alloy 902
• Incoloy A-286
• A286
• Incoloy DS
• AISI 330
• Inconel 706
• Monel 400
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• Forged disks
• Forged tubes
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