Nickel-iron controlled-expansion alloy · open-die forgings
1.3926 Forgings: Alloy 48 / UNS K94800 / NiFe48 Controlled-Expansion Nickel-Iron
1.3926 is a German Werkstoff number for the 48 % nickel-iron controlled-expansion alloy known internationally as Alloy 48, UNS K94800 and ASTM F30 Alloy 48. Its mean coefficient of thermal expansion, about 8.5 ×10-6 /K between 20 °C and 100 °C, is deliberately matched to soft lead and soda-lime glasses, which makes it the standard alloy for glass-to-metal seals and for industrial thermostat elements operating up to 450 °C. It is ferromagnetic, anneals between 850 °C and 1000 °C, and has an inflection point near 460 °C above which the controlled-expansion effect disappears.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges 1.3926 / Alloy 48 into seamless rolled rings up to 2,500 mm outside diameter, discs to 1,800 mm, shafts to 8 m and single pieces to 8,000 kg, supplied annealed with EN 10204 3.1 or 3.2 certification. Contact sales@steelforgepieces.com or 0086-189-2135-9659.
1.3926 / Alloy 48 at a glance
- Alloy family
- Binary Ni-Fe, controlled expansion
- Nominal nickel
- 48 % (adjusted to hit CTE)
- Werkstoff numbers
- 1.3922 · 1.3926 · 1.3927
- UNS number
- K94800
- Product specification
- ASTM F30 · DIN 17745
- Density
- 8.20 g/cm³ (0.296 lb/in³)
- Mean CTE 20–100 °C
- ≈ 8.5 ×10⁻⁶ /K
- Mean CTE 20–300 °C
- ≈ 8.3–9.3 ×10⁻⁶ /K
- Inflection point
- ≈ 460 °C (860 °F)
- Melting point
- ≈ 1450 °C (2640 °F)
- Thermal conductivity
- ≈ 16.7 W/m·K
- Tensile strength, annealed
- ≈ 520 MPa
- Proof strength Rp0.2
- ≈ 260 MPa
- Elongation, annealed
- ≈ 42 %
- Annealing range
- 850–1000 °C, protective atmosphere
- Magnetic
- Yes, ferromagnetic below ≈ 460 °C
- Seals to
- Soft lead & soda-lime glass
- Max thermostat service
- ≈ 450 °C (840 °F)
Values are typical published data for the Alloy 48 chemistry, given for design guidance. Actual delivered properties are stated on the EN 10204 certificate for each heat. See references.
Trademark notice. NILO® is a registered trademark of Special Metals Corporation; Pernifer® and Magnifer® are registered trademarks of VDM Metals; Invar® and SUPRA® are trademarks of their respective owners, and Kovar® is a registered trademark of CRS Holdings. Material made by those companies and sold under those brands is theirs. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as UNS K94800 / ASTM F30 Alloy 48 / W.Nr. 1.3926 (DIN 17745), the same generic chemistry, manufactured independently. We are not affiliated with, sponsored by or endorsed by any of the trademark holders named on this page, and all other brand names referenced remain the property of their respective owners.
What is material 1.3926 (Alloy 48 / UNS K94800)?
1.3926 is a binary nickel-iron alloy containing nominally 48 % nickel with the balance iron, classified as a controlled-expansion or "low expansion" alloy. It belongs to the same family as Invar 36 and Alloy 42, but sits at the high-nickel end of that family, where the expansion coefficient is deliberately raised to match glass rather than driven toward zero.
The physics behind the grade is magnetostriction. Below its Curie transition, a face-centred-cubic Ni-Fe alloy contracts slightly as magnetic ordering builds up, and this contraction partly cancels ordinary thermal expansion. The size of the cancellation depends almost entirely on nickel content: at 36 % Ni the cancellation is nearly complete and you get Invar; at 48 % Ni it is partial, and the residual expansion lands at roughly 8.5 ×10-6 /K, which happens to be the expansion of ordinary soda-lime and soft lead glass. That coincidence is why the grade exists.
Because the effect is magnetic in origin, it switches off. Above the inflection point near 460 °C the alloy becomes paramagnetic, the compensating contraction vanishes, and expansion climbs steeply to values typical of an ordinary austenitic alloy. Every design rule for 1.3926 follows from that single fact: the alloy is used below its inflection point, which is why its practical service ceiling for thermostat work is quoted as about 450 °C.
1.3926 is not a strength alloy, a corrosion alloy or a heat-resisting alloy. It is specified when dimensional behaviour over temperature is the requirement: a hermetic seal that must not crack, a thermostat element that must move predictably, a mould that must hold a composite part to size, an instrument frame that must not drift.
Where forgings fit
Most published data for Alloy 48 describes wire, strip and small bar, because the classic applications are lamp leads and lead frames. Jiangyin Jiangnan Metal Co., Ltd. works at the other end of the size range: open-die forgings and seamless rolled rings in this chemistry, for composite-moulding tooling, vacuum and electron-device housings, large hermetic feedthrough bodies, positioning fixtures and instrument structures where a forged, ultrasonically sound, fully annealed body is required rather than mill product.
Correcting a common error. Several supplier pages list LNG tank membranes and cryogenic transfer lines under Alloy 48. That is wrong. LNG membrane containment uses Invar 36 (1.3912 / UNS K93600), whose expansion is roughly six times lower. Specifying Alloy 48 for a cryogenic containment duty will produce a part that shrinks far more than the design allows.
What are the equivalents of 1.3926? (Alloy 48, UNS K94800, Ni48)
Engineers meet this alloy under a dozen different names. The designations below all describe the same 48 % nickel-iron chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written against any of them, shipping material certified to UNS K94800 / ASTM F30 Alloy 48 / W.Nr. 1.3926.
| Body / region | Designation | Notes |
|---|---|---|
| Germany · DIN 17745 | 1.3922 · 1.3926 · 1.3927 | Three Werkstoff numbers cover this alloy family; 1.3922 is the base Ni48 number and 1.3926 / 1.3927 are the closely related variants. State the exact number you need on the PO. |
| Germany · short name | Ni48 / NiFe48 | Written form of the same grade in DIN 17745 |
| USA · UNS | K94800 | Unified Numbering System, the safest single identifier |
| USA · ASTM | ASTM F30 Alloy 48 | Sheet, strip, rod, bar, tubing and wire of Ni-Fe sealing alloys |
| USA · military | MIL-I-23011 Class 3 | Legacy specification for iron-nickel sealing alloys, confirm current revision status before citing on a PO |
| France · AFNOR | NF A54-301 | French national specification |
| Welding filler | AWS 092 | Matching-composition filler designation |
| Trade names | NILO® 48 · Pernifer® 48 · Magnifer® 50 · Dilaton 48 · Glass Seal 48 · Invar® 48 · SUPRA 50 · Nifemax · Safeni 48 · AL 4750 | Brands of the respective producers. We do not sell under these names, see the trademark notice above. |
Cross-reference compiled from published mill datasheets and materials registers; see references 1–6.
A nuance most pages skip. 1.3922, 1.3926 and 1.3927 are cross-listed as Alloy 48 / K94800, but they are three separate Werkstoff numbers, and some European registers differentiate the chromium-bearing and chromium-free variants within the group. If your drawing was issued in Germany and names a specific number, quote that number on the enquiry. We will reproduce it on the material certificate and, where the difference matters, control the residual chromium accordingly.
🔎 Designation lookup: type any name, get every equivalent
Enter 1.3926, K94800, Alloy 48, Ni48, ASTM F30, NILO 48, Pernifer 48…
Start typing to search the cross-reference table.
What is the chemical composition of 1.3926 / Alloy 48?
Alloy 48 is deliberately simple. Nickel and iron do the work; everything else is a residual that is held down because it interferes with either the expansion curve or the glass-sealing surface. Note that nickel is a target, not a fixed number. The mill adjusts it inside the band to land the expansion coefficient on the customer's requirement, which is why datasheets say "48 nominal" rather than a min/max pair.
| Element | Typical limit | Why it is controlled |
|---|---|---|
| Nickel (Ni) | 48.0 nominal | Sets the expansion coefficient; trimmed within the band to meet the specified CTE |
| Iron (Fe) | Balance | Matrix |
| Cobalt (Co) | ≤ 1.00 | Behaves like nickel in the lattice; counted when trimming the expansion |
| Manganese (Mn) | ≤ 0.80 | Deoxidiser; excess raises expansion and harms glass wetting |
| Silicon (Si) | ≤ 0.30 | Deoxidiser; forms silica in the seal oxide if too high |
| Chromium (Cr) | ≤ 0.25 | Raises expansion and forms a tenacious oxide that resists glass wetting |
| Aluminium (Al) | ≤ 0.10 | Same oxide-forming concern as chromium |
| Carbon (C) | ≤ 0.05 | Causes gas evolution (CO) at the seal interface, kept very low for sealing grades |
| Phosphorus (P) | ≤ 0.025 | Impurity; hot-shortness |
| Sulphur (S) | ≤ 0.025 | Impurity; embrittles nickel alloys at forging temperature |
Limits shown are representative of ASTM F30 Alloy 48 and DIN 17745 practice as published in mill datasheets; individual specifications and revisions differ slightly. Jiangyin Jiangnan Metal Co., Ltd. reports full heat chemistry on every EN 10204 certificate.
Melting route
The grade is melted by EAF + VOD + ESR for general forging work, and by VIM + VAR where the tightest cleanliness and gas content are required, for example vacuum-device parts and hermetic seal bodies, where a single oxide stringer at the seal face is a leak path. Vacuum melting also gives the tightest control on carbon, which is the element most likely to spoil a glass seal by evolving CO during sealing.
Ask for the dilatometer, not just the spectrometer. Chemistry alone does not prove the expansion coefficient. For sealing-critical work, specify a dilatometer trace over your service range on the release documentation. We can supply this as an annex to the EN 10204 certificate. Most competitors will not offer it unprompted.
Thermal expansion of Alloy 48, and which glasses it seals to
The expansion behaviour is the whole point of the alloy, so here are the numbers. Below the inflection point the mean coefficient of thermal expansion is roughly 8.5 ×10-6 /K over 20–100 °C, rising gently to about 8.3–9.3 ×10-6 /K over 20–300 °C. Above roughly 460 °C the curve turns sharply upward.
| Material | Mean CTE | Match with Alloy 48? |
|---|---|---|
| Alloy 48 / 1.3926 (20–100 °C) | 8.5 | reference row |
| Alloy 48 / 1.3926 (20–300 °C) | 8.3 – 9.3 | reference row |
| Soda-lime glass | 8.5 – 9.0 | Matched seal, the design case |
| Soft lead glass | 9.0 – 9.5 | Matched seal, the design case |
| Borosilicate glass (e.g. 3.3) | 3.3 | Mismatch, use Kovar-type NiCo29-18 (1.3981) |
| Fused silica | 0.5 | Severe mismatch, graded seals only |
| Alumina ceramic 94–96 % | 7.0 – 7.6 | Close but not matched, usually Kovar or Alloy 42/46 |
| Silicon | 2.6 – 3.0 | Mismatch, lead frames use Alloy 42 |
| Carbon steel (reference) | 12 | n/a |
| 304 stainless (reference) | 17.3 | n/a |
| Copper (reference) | 16.5 | n/a |
Partner-material values are standard textbook ranges given for comparison only; verify against your own glass or ceramic datasheet, since expansion varies between formulations of the same glass family.
Matched seal, compression seal, or neither
Sealing practice recognises three cases, and the tool below applies the usual rules of thumb:
- Matched seal: metal and glass expansions agree within roughly 0.5 ×10-6 /K. Residual stress is low, and the joint can be thin-walled. This is what Alloy 48 is designed to do with soda-lime and soft lead glass.
- Compression seal: the surrounding metal body has a higher expansion than the glass, so on cooling it squeezes the glass, which is strong in compression. Here a mismatch is intentional, and Alloy 48 is often the pin rather than the body.
- Mismatch: expansion differs enough that cooling puts the glass into tension. Glass fails in tension, so this cracks, sometimes weeks later in service. Choose a different alloy.
🔬 Glass-to-metal seal match checker
Pick the partner material and your service range, then get a matched / compression / mismatch verdict and, if needed, the Ni-Fe alloy that fits instead.
Choose a partner material and press Check the match.
First-pass screening only, based on mean-CTE comparison. A real seal design must also consider glass set point, seal geometry, wall thickness, oxide thickness and cooling rate. Jiangyin Jiangnan Metal Co., Ltd. provides this tool for guidance and cannot accept liability for seal design decisions.
📈 Ni-Fe expansion curve explorer: see the inflection point
Drag the temperature. Watch what happens to Alloy 48 above 460 °C, and how it compares with Invar 36, Alloy 42 and Alloy 52.
Schematic curves built from published mean-CTE data points and the known inflection temperatures of each grade; intended to show behaviour, not to substitute for a measured dilatometer trace on your heat.
What are the physical properties of 1.3926 / Alloy 48?
| Property | Metric | Imperial | Condition / note |
|---|---|---|---|
| Density | 8.20 g/cm³ | 0.296 lb/in³ | Room temperature |
| Melting point | ≈ 1450 °C | ≈ 2640 °F | Approximate |
| Inflection point | ≈ 460 °C | ≈ 860 °F | Expansion curve turns upward here |
| Mean CTE 20–100 °C | 8.5 ×10⁻⁶ /K | 4.7 ×10⁻⁶ /°F | The design value for soda-lime sealing |
| Mean CTE 20–300 °C | 8.3 – 9.3 ×10⁻⁶ /K | 4.6 – 5.2 ×10⁻⁶ /°F | Range depends on exact nickel level |
| Thermal conductivity | ≈ 16.7 W/m·K | ≈ 116 BTU·in/ft²·h·°F | Room temperature |
| Modulus of elasticity | ≈ 150 GPa | ≈ 21.8 ×10⁶ psi | Typical; verify if critical |
| Electrical resistivity | ≈ 0.45 µΩ·m | ≈ 270 Ω·cmil/ft | Typical, indicative only |
| Magnetic behaviour | Ferromagnetic, high permeability | Loses ferromagnetism above the inflection point | |
| Max thermostat service temperature | ≈ 450 °C | ≈ 840 °F | Industrial thermostat practice |
Compiled from published Alloy 48 / NILO 48 / Pernifer 48 datasheets; see references 1–6. Modulus and resistivity are indicative values that vary with processing; request measured data if they drive your design.
What are the mechanical properties of 1.3926 forgings?
Alloy 48 is not hardenable by heat treatment. There is no precipitation reaction to exploit. Strength comes only from cold work, and cold work is exactly what you must remove before service, because residual strain distorts the expansion curve. Controlled-expansion alloys are therefore supplied and used annealed, and the annealed properties below are what a forging will deliver.
| Property | Annealed | Cold worked / hard drawn |
|---|---|---|
| Tensile strength Rm | ≈ 520 MPa (75 ksi) | 700 – 900 MPa (102–131 ksi) |
| Proof strength Rp0.2 | ≈ 260 MPa (38 ksi) | Not normally specified |
| Elongation at break A | ≈ 42 % | Low, depends on reduction |
| Hardness | ≈ 130 – 160 HV (indicative) | Higher, varies with reduction |
| Suitable for service? | Yes, required condition | No, anneal before use |
Annealed values are typical for the Alloy 48 chemistry tested after annealing. Forgings are tested per heat and section; guaranteed values are those on the EN 10204 certificate.
What this means when you write a drawing. Do not specify a minimum tensile strength that implies cold work, and do not specify a hardness range borrowed from a stainless-steel drawing. If the part must carry real load, either increase the section or reconsider the grade. A controlled-expansion alloy chosen for its CTE cannot also be asked to behave like 17-4PH.
1.3926 vs Invar 36, Alloy 42, Alloy 52 and Kovar: which do you need?
Almost every wrong order in this family comes from picking the alloy by name rather than by expansion target. The table lines them up by the only number that matters.
| Grade | W.Nr. | UNS | Ni % | Mean CTE ×10⁻⁶ /K | Inflection | Designed to match |
|---|---|---|---|---|---|---|
| Invar 36 | 1.3912 | K93600 | 36 | ≈ 1.2–1.5 (20–100 °C) | ≈ 230 °C | Nothing, near-zero expansion. LNG membranes, metrology, satellite structures |
| Alloy 42 | 1.3917 | K94100 | 42 | ≈ 5.3 (20–300 °C) | ≈ 300 °C | Silicon, semiconductor lead frames, some ceramics |
| Alloy 46 | 1.3920 | K94600 | 46 | ≈ 7.5 (20–300 °C) | ≈ 400 °C | Intermediate glasses, ceramic-to-metal work |
| Alloy 48 / 1.3926 | 1.3922 · 1.3926 · 1.3927 | K94800 | 48 | ≈ 8.5 (20–100 °C) | ≈ 460 °C | Soda-lime and soft lead glass; thermostats to 450 °C |
| Alloy 52 | 1.3928 | N14052 | 51–52 | ≈ 9.9–10.2 (20–300 °C) | ≈ 500 °C | Higher-expansion soft glasses, lamp and tube work |
| Kovar type NiCo29-18 | 1.3981 | K94610 | 29 Ni + 17 Co | ≈ 5.1–5.5 (20–300 °C) | ≈ 435 °C | Borosilicate glass and alumina ceramic |
Values are nominal published figures for comparison. Jiangyin Jiangnan Metal Co., Ltd. forges all of the grades listed; see Invar 36 and Invar 42.
Choose Invar 36 when…
the requirement is minimum movement: cryogenic containment, metrology frames, laser benches, satellite optics. Not a sealing alloy.
Choose Alloy 42 when…
you are matching silicon or a low-expansion ceramic: lead frames, some hermetic packages, diode headers.
Choose Alloy 48 / 1.3926 when…
you are sealing to ordinary soft glass, or building a thermostat element or composite mould that works below about 450 °C.
🎯 Ni-Fe alloy selector in three questions
Answer three questions and get the grade, the reason, and the specification to quote.
Answer the three questions and press Recommend a grade.
How is 1.3926 / Alloy 48 annealed and stabilised?
Annealing is carried out between 850 °C and 1000 °C in a protective atmosphere, followed by air or water cooling. Time at temperature scales with section: roughly half an hour for thin product, and about 30 minutes per 25 mm of section for forgings, plus soak-through time for heavy pieces.
| Operation | Temperature | Time | Purpose |
|---|---|---|---|
| Full anneal | 850 – 1000 °C | ≈ 30 min per 25 mm | Recrystallise, remove forging and machining strain, restore the expansion curve |
| Wet-hydrogen anneal | ≈ 1000 – 1100 °C | 15 – 60 min | Decarburise the surface and grow a controlled adherent oxide for glass wetting |
| Stabilising / stress relief | ≈ 500 – 550 °C | 1 – 4 h | Dimensional stabilisation of precision parts after final machining |
| Not applicable | n/a | Quench hardening, ageing, precipitation hardening, the alloy does not respond to any of them | |
Annealing range per published Alloy 48 datasheets; the wet-hydrogen and stabilising cycles reflect standard glass-sealing and precision-instrument practice and should be qualified for your part.
Why cooling rate matters more than usual
In most alloys the annealing cool-down affects hardness. Here it affects dimensions. Ni-Fe controlled-expansion alloys carry a slow, temperature-dependent dimensional drift after thermal cycling, which is why precision parts get a stabilising soak after final machining. If your part has to hold a tolerance for years, say so on the enquiry. The extra cycle costs little and prevents an expensive field surprise.
🔥 Anneal recipe generator
Enter section thickness and duty. Get a printable cycle for your heat-treatment shop.
Enter a thickness and press Generate the cycle.
Starting parameters based on the published 850–1000 °C annealing range and normal soak-time practice. Qualify on test pieces before production; final acceptance is by measured properties, not by cycle alone.
How is 1.3926 forged?
Alloy 48 forges like a soft austenitic nickel alloy: it moves easily but it is unforgiving about two things: sulphur and finishing temperature.
| Parameter | Value | Reason |
|---|---|---|
| Heating temperature | 1120 – 1200 °C | Full solution of the Ni-Fe matrix, low flow stress |
| Finishing temperature | ≥ 900 °C | Below this the alloy work-hardens quickly and surface cracking risk rises |
| Forging ratio | ≥ 4 : 1 | Break down the as-cast structure and refine grain size |
| Furnace atmosphere | Sulphur-free fuel | Nickel-rich alloys suffer sulphur embrittlement at forging heat, a classic cause of cracked billets |
| Post-forge | Anneal 850 – 1000 °C | Removes forging strain and restores the expansion curve |
| Ultrasonic testing | EN 10228-3 · SEP 1921 · ASTM A388 | Performed after anneal and rough machining |
Forging window reflects standard hot-working practice for 48 % Ni-Fe alloys; exact schedule is set per part geometry and ingot size.
Process routes we use for this grade
- Open-die forging: shafts, blocks, stepped bodies, large discs. The default for one-off and low-volume parts.
- Seamless ring rolling: rings from 200 mm to 2,500 mm outside diameter. The most common route for mould rings, housing bodies and flange blanks.
- Upset forging: short, large-section discs and hubs.
- Near-net-shape forging: worth doing on this grade, because Alloy 48 costs far more per kilogram than steel and 30–50 % less machining stock is a real saving.
Machining, welding and surface preparation
Machining
Alloy 48 machines like a gummy austenitic alloy. It is soft, it work-hardens, and it forms long stringy chips. Practical settings: sharp positive-rake carbide, moderate speeds (roughly 30–60 m/min turning), heavy positive feed so the tool cuts under the hardened layer rather than rubbing on it, rigid setups, and generous flood coolant. Never dwell. Take a stabilising cycle after final machining if the part is a precision one.
Welding
The alloy is readily fusion welded by GTAW with matching filler (AWS 092 designation). Keep heat input low and the joint clean, because sulphur, lead and other low-melting contaminants cause hot cracking in high-nickel weld metal. Weld before final annealing wherever possible, so the anneal also relieves the weld. Note that weld metal and heat-affected zone will not have exactly the same expansion coefficient as parent metal; for sealing-critical parts, keep welds away from the seal zone.
Surface preparation for glass sealing
A glass-to-metal seal is really a glass-to-oxide seal. The metal is given a wet-hydrogen treatment to decarburise the surface and grow a thin, adherent, dissolvable oxide that the molten glass wets and takes into solution. Too little oxide and the glass does not bond; too much and the seal fails within the oxide layer. If your parts go on to a sealing line, tell us at enquiry stage, because surface condition, cleanliness and packaging all change.
What forged products are available in 1.3926 / Alloy 48?
Jiangyin Jiangnan Metal Co., Ltd. supplies the following shapes in 1.3926 / Alloy 48 / UNS K94800, all delivered annealed unless the order says otherwise:
- Seamless rolled rings
- Contoured rolled rings
- Forged rings
- Forged discs & blanks
- Forged shafts & spindles
- Forged round bars
- Forged flanges
- Forged sleeves & bushings
- Forged tube sheets
- Forged pipes & hollow bodies
- Forged blocks
- Near-net-shape forgings to drawing
| Product form | Size range | Typical use in this grade |
|---|---|---|
| Seamless rolled ring | 200 – 2,500 mm OD | Composite mould rings, housing bodies, flange blanks |
| Forged disc | up to Ø 1,800 mm | Tooling plates, instrument bases, seal-body blanks |
| Forged shaft | up to 8 m long | Thermostat rods, positioning shafts, instrument spindles |
| Round bar | Ø 25 – 500 mm | Machining stock for feedthroughs, pins, bushings |
| Single-piece weight | up to 8,000 kg | Heavy tooling and structural forgings |
| Wall / height limits | Ring height to 600 mm, min wall 30 mm | Ring-mill envelope |
Sizes are the qualified envelope of our forging and ring-rolling equipment. Send the drawing and we will confirm feasibility, including whether a trepanned billet reduces your material cost.
⚖️ 1.3926 forging weight calculator
Density 8.20 g/cm³. Pick a shape, enter dimensions, get net weight plus a realistic forging billet weight for your RFQ.
Result is the net finished weight at 8.20 g/cm³. Allow roughly 20–35 % extra for machining stock on the rough forging, more on complex profiles. Maximum single-piece capability is 8,000 kg.
Where is 1.3926 / Alloy 48 used?
Every application below traces back to the same property: an expansion coefficient near 8.5 ×10-6 /K that stays put until roughly 460 °C.
Glass-to-metal seals
The original and still dominant use. Soft lead and soda-lime glass seals in electric lamp bulbs, electron and vacuum tubes, relay and switch housings, hermetic feedthroughs and specialty sealed devices. Forged bodies and rolled rings supply the metal side of larger seals.
Industrial thermostats to 450 °C
Thermostat rods, bimetal strip components and temperature-actuated elements. The alloy provides the low-expansion leg of a bimetal pair, and its useful ceiling is set by the inflection point.
Composite moulding tooling
Moulds and mandrels for aerospace composite lay-up, where the tool must return the cured part to the designed dimension. Forged rings and discs are the usual blanks.
Precision instruments & positioning
Instrument frames, positioning devices, metrology fixtures, clock and timing components, anything where thermal drift shows up directly in the measurement.
Electronic packaging
Lead frames, headers, housings and resonator bodies where the metal must live alongside glass or ceramic without opening a leak path on thermal cycling.
Magnetic components
Magnetic shielding, small transformer and inductor cores, relay parts, a side benefit of the high nickel content and the ferromagnetism that underlies the expansion behaviour.
What Alloy 48 is not for. Cryogenic containment (use Invar 36), pressure-containing service at temperature, seawater or acid corrosion service, structural load-bearing parts, and anything running continuously above about 450 °C. For high-temperature strength look at Incoloy A-286, Inconel 706 or Inconel 625; for corrosion, Hastelloy C-276 or Incoloy 825.
Ten mistakes engineers make when ordering 1.3926 forgings
Collected from RFQs and post-delivery reviews. Each of these costs weeks if it is caught at goods-in instead of at the specification stage.
1. Ordering by trade name alone
A purchase order that says only "NILO 48" or "Pernifer 48" can strictly only be filled by the trademark owner. Fix: write "UNS K94800 / ASTM F30 Alloy 48 / W.Nr. 1.3926", and add the trade name in brackets as a reference only.
2. Confusing Alloy 48 with Invar 36
Both are "Invar-family" nickel-iron alloys and some catalogues even list Alloy 48 as "Invar 48". Their expansion differs by roughly a factor of six. Fix: specify the required CTE and the temperature range on the drawing, not just the alloy name.
3. Specifying a tensile minimum that implies cold work
Cold work raises strength but distorts the expansion curve, and the alloy has to be annealed before service anyway. Fix: accept the annealed properties, and size the part for them.
4. Using it above the inflection point
Above roughly 460 °C the controlled-expansion behaviour is simply gone. A part qualified at 300 °C can behave completely differently at 500 °C. Fix: keep continuous service below about 450 °C, or change grade.
5. Ignoring the chromium and aluminium residuals for sealing work
Chromium and aluminium form tenacious oxides that glass will not wet or dissolve properly, so a heat that passes the chemistry table can still fail on the sealing line. Fix: for sealing duty, state a tighter Cr and Al limit on the enquiry.
6. Forgetting the wet-hydrogen surface treatment
Parts arrive bright and clean, and are then found not to wet. Fix: state on the order whether we should supply as-annealed, or hydrogen-treated and packaged for a sealing line.
7. Machining to final size before the stabilising cycle
Ni-Fe alloys drift dimensionally after thermal cycling. Fix: rough machine, anneal, stabilise, then finish machine, and say so in the sequence of operations.
8. Welding across a seal zone
Weld metal and heat-affected zone do not have parent-metal expansion. A seal that crosses a weld will eventually crack. Fix: design welds away from seal faces, or forge the body in one piece, which is exactly what a rolled ring is for.
9. Sulphur-bearing furnace fuel or marking media
High-nickel alloys embrittle badly with sulphur pickup at forging temperature. It also arrives from grease pencils and some marking paints. Fix: require sulphur-free fuel and low-sulphur marking on the order.
10. No UT acceptance class on the drawing
"Ultrasonically tested" means nothing without a standard and a class. Fix: state EN 10228-3, SEP 1921 or ASTM A388 plus the acceptance class. The picker below suggests one.
Production capability for 1.3926 / Alloy 48 forgings
Jiangyin Jiangnan Metal Co., Ltd. has operated as an open-die forging factory in Jiangyin, Jiangsu since 2008, employing around 460 people including senior and intermediate engineers, and exporting to more than 40 countries. Raw material, forging, heat treatment, machining and inspection are organised on one site, which is what makes small-quantity nickel-alloy work practical.
Process flow for a 1.3926 forging
Raw material
EAF + VOD + ESR, or VIM + VAR for sealing-critical work. Heat number recorded; chemistry verified on our own spectrometer before the billet is cut.
Heating and forging
1120–1200 °C, sulphur-free fuel, finishing above 900 °C, forging ratio ≥ 4:1. Open-die, ring rolling or upsetting according to geometry.
Anneal
850–1000 °C in protective atmosphere, soak scaled to section, air or water cool. Furnace chart recorded and issued with the certificate.
Rough machining
Stock left for finish machining; surfaces prepared so ultrasonic testing is meaningful.
Non-destructive testing
Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus surface penetrant or magnetic-particle examination where specified.
Mechanical and physical testing
Tensile and hardness testing per heat and section; dilatometer expansion verification when ordered.
Stabilising (if required)
500–550 °C stabilising soak for precision parts, after final machining.
Certification, marking and packing
EN 10204 3.1 or 3.2, low-sulphur marking, packing suited to the destination and to any downstream sealing operation.
Equipment
| Area | Equipment | Capability |
|---|---|---|
| Forging | Open-die forging hammers, 1 t · 3 t · 5 t · 9 t | Shafts, blocks, discs, stepped bodies |
| Forging | Hydraulic forging press, 5,000 t | Heavy sections; single pieces to 8,000 kg |
| Ring rolling | Seamless ring-rolling mills, 3 m and 6 m | Rings 200–2,500 mm OD, height to 600 mm, min wall 30 mm |
| Heat treatment | Protective-atmosphere annealing furnaces | 850–1000 °C anneal with recorded charts |
| NDT | Ultrasonic flaw detection; magnetic-particle detector | EN 10228-3 · SEP 1921 · ASTM A388 |
| Laboratory | Universal testing machine; impact tester; hardness testers; metallographic microscope; optical emission spectrometer | Chemistry, tensile, impact, hardness, grain size |
| Machining | CNC turning, milling, boring and grinding | Rough, semi-finish and finish machining to drawing |
Equipment list as published by Jiangyin Jiangnan Metal Co., Ltd. Visits and witnessed inspection are welcome by arrangement.
Which standards and quality documents apply to 1.3926 forgings?
Material specifications
- ASTM F30, Alloy 48 (Ni-Fe sealing alloys)
- DIN 17745, W.Nr. 1.3922 / 1.3926 / 1.3927
- AFNOR NF A54-301
- UNS K94800
Testing and certification
- EN 10228-3, UT of austenitic and austenitic-ferritic forgings
- SEP 1921, UT of steel forgings
- ASTM A388, UT practice for steel forgings
- EN 10204 3.1 standard, 3.2 with third-party witness
- ISO 9001:2015 quality management
Third-party witnessed certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Because expansion is the functional property of this grade, we also offer a dilatometer trace annexed to the certificate, covering the temperature range you specify.
Quality gates. Every 1.3926 order passes hold points at chemistry verification, forging temperature, post-anneal ultrasonic testing, heat-treatment chart approval, mechanical test acceptance and final dimensional inspection. Customer-witnessed hold points can be added at no charge. Non-conformances are reported to the customer with a proposed disposition before any rework is carried out.
🧭 Ultrasonic acceptance class picker
Turn "must be UT tested" into a defensible line on the drawing.
Pick a standard family and press the button.
Suggestion only. The acceptance class that governs is the one written in your project specification or design code; where they conflict, the project specification wins.
How to specify a 1.3926 / Alloy 48 forging order
Seven lines on the enquiry remove almost all the ambiguity that causes rework on this grade.
State the designation in full
“UNS K94800 / ASTM F30 Alloy 48 / W.Nr. 1.3926 (DIN 17745)”. Trade names go in brackets as a reference, never as the ordering designation.
State the expansion requirement
Give the partner material, or the required mean coefficient of thermal expansion and the temperature range over which it applies. Nickel is trimmed inside the band to hit this, so if you do not state it, you get the nominal.
State the delivery condition
“Annealed 850–1000 °C, protective atmosphere.” Add “hydrogen treated for glass sealing” or “stabilised for dimensional stability” if either applies.
Provide geometry
Drawing or 3D model with finished dimensions, tolerances, surface roughness and machining allowance. For rings: OD, ID and height.
Define testing
Chemistry, tensile, ultrasonic standard and acceptance class, surface NDT if required, and dilatometer verification for sealing-critical work.
Specify certification
EN 10204 3.1, or 3.2 with a named third-party inspection body.
Give commercial detail
Quantity, required delivery date, Incoterms and destination port, so the quotation reflects a real lead time rather than a default one.
Drawing callout template
Copy this into the material block of your drawing and edit the values in capitals.
MATERIAL: UNS K94800 / ASTM F30 ALLOY 48 / W.Nr. 1.3926 (DIN 17745)
Ni 48 % nominal, Fe balance, controlled-expansion Ni-Fe
EXPANSION: MEAN CTE 8.5 x 10-6 /K OVER 20-100 DEG C
VERIFY BY DILATOMETER OVER 20-300 DEG C [DELETE IF NOT REQUIRED]
CONDITION: ANNEALED 850-1000 DEG C, PROTECTIVE ATMOSPHERE, AIR COOL
[ADD: WET-HYDROGEN TREATED FOR GLASS SEALING]
[ADD: STABILISED 500-550 DEG C AFTER FINISH MACHINING]
RESIDUALS: Cr MAX 0.15 %, Al MAX 0.05 %, C MAX 0.03 % [SEALING DUTY ONLY]
NDT: UT PER EN 10228-3 QUALITY CLASS 3 [OR SEP 1921 / ASTM A388 + CLASS]
PT PER EN ISO 3452 ON MACHINED SURFACES [IF REQUIRED]
CERTIFICATE: EN 10204 3.1 [OR 3.2 WITNESSED BY: ______ ]
MARKING: HEAT NUMBER + GRADE + DRAWING NUMBER, LOW-SULPHUR MARKING MEDIA ONLY
NOTE: DO NOT SUBSTITUTE INVAR 36 / ALLOY 42. EXPANSION IS THE FUNCTIONAL
REQUIREMENT OF THIS PART.
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Glossary
- Controlled-expansion alloy
- An alloy selected for a specified coefficient of thermal expansion rather than for strength or corrosion resistance. Also called a low-expansion alloy.
- Werkstoff number
- The German material number, here 1.3926. The prefix 1.3 covers special alloy steels and nickel-iron alloys in the DIN system.
- UNS K94800
- The Unified Numbering System identifier for the 48 % nickel-iron sealing alloy, the least ambiguous way to name this material.
- Inflection point
- The temperature, near 460 °C for Alloy 48, at which the magnetostrictive contraction that suppresses thermal expansion disappears and the expansion curve turns sharply upward.
- Matched seal
- A glass-to-metal joint in which both materials have essentially the same expansion, so cooling leaves little residual stress.
- Compression seal
- A joint in which the metal body deliberately has higher expansion than the glass, so cooling puts the glass into compression, the state in which glass is strongest.
- Wet-hydrogen anneal
- A treatment in humidified hydrogen that decarburises the surface and grows a thin adherent oxide the molten glass can wet and dissolve.
- Dilatometer
- The instrument that measures length change against temperature, producing the expansion curve that this alloy is bought for.
- EN 10204 3.1 / 3.2
- Inspection-document types: 3.1 is issued by the manufacturer's independent inspection function; 3.2 is countersigned by a third party or the purchaser's representative.
- Seamless rolled ring
- A ring produced by piercing a forged billet and rolling it out on a ring mill, giving circumferential grain flow with no weld.
- ESR / VAR
- Electroslag remelting and vacuum arc remelting, secondary melting routes that clean up inclusions and improve homogeneity.
Frequently asked questions about 1.3926 / Alloy 48
What is material 1.3926?
1.3926 is a German Werkstoff number for the 48 % nickel-iron controlled-expansion alloy known internationally as Alloy 48, UNS K94800 and ASTM F30 Alloy 48. Its coefficient of thermal expansion, about 8.5 ×10⁻⁶ /K between 20 °C and 100 °C, closely matches soft lead and soda-lime glasses, which makes it the standard material for glass-to-metal seals and for industrial thermostat elements up to 450 °C. Jiangyin Jiangnan Metal Co., Ltd. open-die forges this alloy into rings, discs, shafts, flanges and bars.
Are 1.3926, 1.3922, 1.3927, Alloy 48 and UNS K94800 the same material?
Yes, they describe the same 48 % nickel-iron chemistry. DIN 17745 covers it under the Werkstoff numbers 1.3922, 1.3926 and 1.3927; the Unified Numbering System assigns K94800; ASTM F30 lists it as Alloy 48; AFNOR uses NF A54-301. Because the three Werkstoff numbers cover minor variants inside the same family, state the exact number you need on the purchase order and we will reproduce it on the certificate.
What is the chemical composition of 1.3926 / Alloy 48?
Nickel is nominally 48 % and trimmed within the band to meet the required expansion; iron is the balance. Typical residual limits are carbon 0.05 % max, manganese 0.80 % max, silicon 0.30 % max, chromium 0.25 % max, aluminium 0.10 % max, cobalt 1.00 % max, phosphorus 0.025 % max and sulphur 0.025 % max. Jiangyin Jiangnan Metal Co., Ltd. melts the alloy by EAF + VOD + ESR, or by VIM + VAR where the tightest cleanliness is required.
What is the coefficient of thermal expansion of Alloy 48?
Approximately 8.5 ×10⁻⁶ /K over 20–100 °C, and about 8.3–9.3 ×10⁻⁶ /K over 20–300 °C. The curve stays low and nearly linear up to the inflection point near 460 °C, above which the alloy loses its ferromagnetic ordering and expansion rises steeply.
What glass does Alloy 48 seal to?
Soft lead glasses and soda-lime glasses, whose expansion is roughly 8.5–9.5 ×10⁻⁶ /K. It is not correct for borosilicate glass or alumina ceramic, which are matched by the nickel-iron-cobalt Kovar type NiCo29-18 (1.3981 / K94610), and it is not correct for silicon, which is closer to Alloy 42.
Is 1.3926 the alloy used for LNG membrane tanks?
No. LNG membrane containment and cryogenic transfer lines use Invar 36 (W.Nr. 1.3912, UNS K93600), the 36 % nickel alloy with near-zero expansion. Alloy 48 expands roughly six times more and is a glass-sealing and thermostat alloy. This is the most common mix-up in nickel-iron procurement.
What are the mechanical properties of annealed 1.3926?
Typically tensile strength about 520 MPa, 0.2 % proof strength about 260 MPa and elongation about 42 %. Cold-worked material reaches 700–900 MPa but must be annealed before service, because retained cold work distorts the expansion curve the alloy is chosen for.
How is 1.3926 annealed?
Between 850 °C and 1000 °C in a protective atmosphere. Allow roughly 30 minutes for thin product and about 30 minutes per 25 mm of section for forgings, followed by air or water cooling. Parts destined for glass sealing usually receive an additional wet-hydrogen anneal to decarburise the surface and develop a controlled adherent oxide.
What forged shapes and sizes are available?
Seamless rolled rings up to 2,500 mm outside diameter, forged discs to 1,800 mm diameter, forged shafts up to 8 m long, round bars from 25 to 500 mm diameter, plus flanges, sleeves, bushings, tube sheets and near-net-shape forgings, with single-piece weights up to 8,000 kg.
What certification is supplied?
Standard supply is an EN 10204 3.1 mill certificate covering heat chemistry, mechanical results, heat-treatment records and ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388. EN 10204 3.2 certificates witnessed by Lloyd's, DNV, BV, ABS, TÜV or SGS are available on request, as is a dilatometer trace of the expansion curve.
Is Alloy 48 magnetic?
Yes. It is ferromagnetic with high permeability at room temperature, which is why it also serves for magnetic shielding and small transformer cores. Its ferromagnetism is the physical origin of the controlled expansion, and both disappear above the inflection point near 460 °C.
Can Alloy 48 be welded and machined?
Yes to both. GTAW with matching filler (AWS 092 designation) works well provided heat input is low and the joint is free of sulphur and other low-melting contaminants. Machining behaves like a soft austenitic alloy: sharp positive-rake carbide, moderate speed, heavy positive feed, flood coolant, no dwelling.
What is the lead time and how do I get a quotation?
Typically 8–10 weeks for standard annealed forgings and rolled rings, extending to 12–14 weeks with third-party witnessed 3.2 certification, dilatometer verification, or single pieces above 3 tonnes. Email sales@steelforgepieces.com or call 0086-189-2135-9659. Quotations are issued within 24 hours.
References and how this page is maintained
Property values on this page are compiled from published standards and mill datasheets for the Alloy 48 / UNS K94800 chemistry. Where sources differ, the wider range is shown and the value is labelled indicative. Test results issued on our own certificates are independent measurements traceable to calibrated equipment.
- ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys, ASTM International, West Conshohocken, PA.
- DIN 17745, Wrought nickel-iron alloys with specified thermal expansion, Deutsches Institut für Normung, Berlin.
- Special Metals Corporation, NILO and NILOMAG alloys technical bulletin (designations UNS K94800, W.Nr. 1.3922 / 1.3926 / 1.3927; ASTM F30).
- VDM Metals, Pernifer 48 / Magnifer 50 material data sheets.
- Alloy Wire International, Nilo 48 datasheet (density, melting point, inflection point, thermal conductivity, expansion coefficients, annealing cycle).
- BIBUS Metals, Nickel Alloy 48 product data (composition limits, density).
- AFNOR NF A54-301, French specification for nickel-iron controlled-expansion alloys.
- EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN, Brussels.
- SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt.
- ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
- EN 10204, Metallic products, Types of inspection documents, CEN.
- ASM Handbook, Volume 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International, chapter on controlled-expansion alloys.
Standards are cited without revision numbers because revisions change; for procurement, always reference the revision in force at the contract date. Trademarks named on this page belong to their respective owners.
Citing this page
Engineers and technical authors are welcome to quote this page with attribution:
Jiangyin Jiangnan Metal Co., Ltd. (2026). "1.3926 Forgings: Alloy 48 / UNS K94800 / NiFe48
Controlled-Expansion Nickel-Iron." Technical data sheet, updated 6 August 2026.
https://www.steelforgepieces.com/Nickel-Alloy/1.3926.html
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, operating since 2008 with a workforce of around 460 including senior and intermediate engineers. The plant covers raw material control, open-die forging on 1–9 tonne hammers and a 5,000 tonne hydraulic press, seamless ring rolling on 3 m and 6 m mills, protective-atmosphere heat treatment, CNC machining and a full mechanical and metallurgical laboratory.
Grades forged in-house range from carbon and alloy steels through tool steels and stainless steels to nickel alloys, including the controlled-expansion family: Invar 36, Invar 42 and Alloy 48 / 1.3926. Quality management is certified to ISO 9001:2015 and material is released against EN 10204 3.1 or 3.2 documentation. Exports go to more than 40 countries.
Jiangyin Jiangnan Metal Co., Ltd.No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone: 0086-189-2135-9659 · Email: sales@steelforgepieces.com · Web: www.steelforgepieces.com
Request a quote for 1.3926 / Alloy 48 forgings
Send the drawing, or just the sizes and quantity. We reply within 24 hours with price, lead time and confirmation of the standards we will certify against. If expansion is the functional requirement, tell us the temperature range and the partner material. That is the part of the specification most enquiries leave out.
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