Alloy 46 / Nilo 46 / UNS K94600 Forging Parts: Controlled-Expansion Forgings for Glass-to-Metal Seals
Alloy 46 (UNS K94600, ASTM F30, GB 4J46, widely sold under the trademarks Nilo® 46, Pernifer® 46 and Glass Sealing 46) is a binary iron-nickel controlled-expansion alloy of nominally 46 % nickel, balance iron. Its mean coefficient of thermal expansion is about 7.5 × 10−6/°C and stays nominally constant up to its Curie point at 460 °C, which makes it the standard sealing alloy for soft lead and soda-lime glasses in electronic tubes, lamps, hermetic packages and feedthroughs. It is a solid-solution alloy and cannot be age hardened. It is supplied annealed, because residual cold work distorts the expansion curve.
- Nominal Ni
- 46 %balance Fe
- Mean CTE 30–450 °C
- 7.5× 10⁻⁶ /°C
- Curie point
- 460 °C860 °F, CTE inflection
- Density
- 8.17g/cm³
- Melting point
- 1427 °C2600 °F
- Tensile, annealed
- 552MPa min (80 ksi)
- Rolled ring OD
- 200–2500mm
- Certification
- 3.1 / 3.2EN 10204
460 °C is both the Curie point and the inflection point of the expansion curve. Below it the alloy holds a low, nominally flat coefficient. Above it the alloy becomes paramagnetic and the coefficient rises from 7.5 to 9.8 × 10−6/°C by 600 °C. A seal designed on the room-temperature figure but processed or operated above 460 °C will not behave as the datasheet predicts.
What is Alloy 46 / Nilo 46 / UNS K94600?
Alloy 46 is a binary iron-nickel alloy, nominally 46 % nickel with the balance iron. It belongs to the controlled-expansion family that begins with Invar 36 and runs through Alloy 42, 46, 48 and 52. The grades differ from one another only in nickel content. Nickel sets the Curie temperature, the Curie temperature sets where the expansion curve bends, and the shape of that curve decides which glass or ceramic the alloy can be sealed to. Alloy 46 is specified for its expansion behaviour, not for strength, corrosion resistance or temperature capability.
The mechanism is the Invar effect, described by Charles-Édouard Guillaume in 1896. In a ferromagnetic iron-nickel alloy, magnetostriction opposes ordinary thermal expansion: as the lattice expands with temperature, the magnetic ordering contracts it. The two effects partly cancel and the net expansion is lower than either iron or nickel alone would give. The cancellation holds only while the alloy is ferromagnetic. At the Curie point the magnetic ordering disappears, the compensation stops, and expansion reverts to normal metallic behaviour. In Alloy 46 that transition occurs at about 460 °C (860 °F).
Invar 36 has the lowest expansion of the family, but its Curie point is only about 220 °C, so its flat range ends early. Raising nickel raises both the expansion coefficient and the Curie point. At 46 % Ni the coefficient reaches roughly 7.5 × 10−6/°C, which is not low in absolute terms, but the flat range extends to 460 °C and 7.5 sits close to the expansion of soft lead and soda-lime glasses. Alloy 46 trades low expansion for a wider flat range and a glass match.
Two consequences follow, and between them they account for most field problems. First, Alloy 46 cannot be hardened by heat treatment. It is a single-phase solid solution with no aluminium or titanium to precipitate γ′, so no thermal cycle raises its strength. Strength comes only from cold work, which is what a controlled-expansion part must not retain, because residual strain distorts the expansion coefficient. Every Alloy 46 forging therefore leaves our works annealed, and a request for hardened Alloy 46 is treated as a specification error and queried before production starts.
Second, the alloy contains no chromium, so it has no passive film and no meaningful corrosion resistance. It rusts in damp air like a plain carbon steel. Sealing components are normally plated, oxidised or hermetically enclosed, and stock parts need oiling or VCI packaging. This is a property of any binary Fe-Ni alloy, not a quality defect, but buyers coming from stainless or nickel-alloy work often do not expect it.
What Forged Products Are Available in Alloy 46 / UNS K94600?
Jiangyin Jiangnan Metal manufactures UNS K94600 by two forging routes chosen by geometry and quantity. Open-die forging covers bars, blocks, shafts, discs and blanks, and is the route used for tube sheets, header plates and machined seal bodies. Seamless hot ring rolling produces forged rings with continuous circumferential grain flow, which is the preferred form for seal rings, flange blanks and housing bodies. Open-die forging requires no dies, so a single prototype piece carries no tooling cost and no tooling lead time. That suits the small development quantities common in sealing and electronics work.
Seamless rolled rings
200–2,500 mm OD, rectangular or contoured section. Seal rings, header rings, flange blanks and housing bodies.
Forged discs & blanks
To 1,800 mm diameter. Covers, base plates, machining blanks for feedthrough bodies and hermetic housings.
Tube sheets & plates
Forged and ultrasonically tested before drilling, for exchangers where the tube and shell expansions must be matched.
Round & flat bar, blocks
25–500 mm Ø round bar, forged flats and blocks, annealed, as-forged or peeled for CNC stock.
Forged shafts & spindles
Dimensionally stable shafts, spindles and mandrels for precision instruments and metrology fixtures.
Sleeves, bushings, hollow bar
Trepanned or bored sleeves, bushings, spacers and near-net blanks to drawing.
The dimensions above are the capability of the works and are stated for the whole nickel-alloy range. Alloy 46 orders sit at the small end of that envelope, since most sealing and electronic components are rings and discs well under 600 mm. The full range is listed because tube sheets and large housings do occasionally come up. An 80 mm diameter part is a normal order, not a small one.
What Are the Equivalents of Alloy 46? (UNS K94600, ASTM F30, 4J46)
Alloy 46 appears on drawings under at least a dozen names. Every designation in the table below refers to the same 46 % nickel iron-nickel chemistry, and Jiangyin Jiangnan Metal accepts purchase orders under all of them, issuing a multi-designation material test certificate that lists each specification the heat satisfies.
| Standard / body | Designation | Scope & notes |
|---|---|---|
| Brand (trademark) | Nilo® 46 | Registered trademark of Special Metals Corporation. We do not sell under this name; we ship the generic equivalents below. |
| Brand (trademark) | Pernifer® 46 | VDM Metals brand name for the same chemistry. |
| Brand (trademark) | Glass Sealing 46, CarTech® Glass Sealing 46 | Carpenter Technology brand names for the same chemistry. |
| Common usage | Invar 46, 46 Alloy, Fe-46Ni | Generic trade usage; "Invar" strictly refers to the 36 % grade but is loosely applied across the family |
| USA · UNS | K94600 | Generic Unified Numbering System designation, the safest way to specify |
| USA · ASTM | ASTM F30 | Iron-nickel sealing alloys: sheet, strip, rod, bar, tubing and wire. The primary specification for this grade |
| USA · AMS | AMS I-23011 Class 4 | Aerospace equivalent of the military specification |
| USA · Military | MIL-I-23011 Class 4 | Legacy US military spec for magnetic and sealing Fe-Ni alloys; still cited on defence and space drawings |
| China · GB | 4J46 | GB designation for the 46 % Ni glass-sealing expansion alloy (4J series covers controlled-expansion alloys) |
| Composition name | NiFe46 · Ni46 | Descriptive designation used on some European drawings |
🔎 Multi-standard designation lookup
Type any designation from a drawing (UNS number, GB code, trade name or specification) to see which alloy it is and whether it is the same material as Alloy 46.
Equivalents are given for identification and enquiry purposes. Chemistry limits and product-form scope differ between standards. Confirm the specific standard edition the order is placed against.
What Is the Chemical Composition of Alloy 46 / UNS K94600?
Alloy 46 is a simple alloy by design. Nickel controls the expansion behaviour and every other element is held low so that nothing interferes with it or with the sealing surface. There is no chromium to form a passive film, no aluminium or titanium to precipitate, no molybdenum and no cobalt addition. The limits below follow ASTM F30.
| Element | Weight % | Function / why the limit exists |
|---|---|---|
| Nickel (Ni) | 46.0 nom. | Sets the Curie point and therefore the whole expansion curve. A ±0.5 % shift moves the coefficient measurably |
| Iron (Fe) | Balance | The other half of the binary system |
| Manganese (Mn) | 0.80 max | Deoxidiser and sulfur scavenger; kept low because it lowers the Curie point |
| Silicon (Si) | 0.30 max | Deoxidiser; excess forms silicate inclusions that spoil sealing surfaces |
| Chromium (Cr) | 0.25 max | Residual only. Any real chromium addition would form an oxide that prevents glass wetting |
| Aluminium (Al) | 0.10 max | Residual deoxidiser; alumina inclusions are a defect in sealing surfaces |
| Carbon (C) | 0.05 max | Kept low so the part can be decarburised before sealing. Surface carbon produces CO gas bubbles in the glass |
| Phosphorus (P) | 0.025 max | Embrittling residual |
| Sulfur (S) | 0.025 max | Hot-shortness during forging; also segregates to the sealing surface |
Cobalt, where present, is an incidental element and is reported separately on the material test certificate. Our ESR route routinely achieves S and P well inside the ASTM F30 ceilings; actual heat analysis appears on the EN 10204 certificate.
In most alloys a 0.05 % carbon maximum would be a mechanical-property limit. Here it controls gas evolution. Residual carbon at the metal surface reacts with the oxide layer during glass sealing and releases carbon monoxide, which appears as bubbles at the seal interface and destroys hermeticity. Sealing-grade Fe-Ni parts are therefore decarburised in wet hydrogen before sealing. The seal surface preparation tool below gives a starting route.
What Are the Mechanical Properties of Alloy 46 Forgings?
Mechanically Alloy 46 is comparable to an annealed austenitic stainless in strength and rather more ductile. It is not specified for strength. The values below are typical room-temperature properties in the annealed condition, which is the only condition in which controlled-expansion forgings should be supplied.
| Property | Metric | Imperial | Note |
|---|---|---|---|
| Tensile strength | 552 MPa min | 80 ksi min | Typical annealed value |
| Yield strength (0.2 % offset) | 242 MPa min | 35 ksi min | Low; design accordingly |
| Elongation in 50 mm | 30 % min | 30 % min | Very ductile; forms and spins well |
| Hardness, annealed | ≈ HRB 80 | ≈ HRB 80 | Soft; protect machined surfaces in handling |
| Modulus of elasticity | ≈ 159 GPa | ≈ 23 × 10³ ksi | Below carbon steel; deflection matters in thin seal flanges |
There is no solution-treat-and-age cycle for Alloy 46. It is a single-phase binary solid solution with no γ′-forming elements. If a drawing calls for solution treatment and ageing, or quotes an aged hardness, the specification has usually been copied from an age-hardenable alloy such as NI-SPAN-C Alloy 902 or Alloy K-500. We query this before accepting the order.
Higher strength in Alloy 46 is available only from cold work, and cold work destroys the expansion accuracy. Where a part needs both strength and controlled expansion, this alloy family cannot provide both and the design has to carry the load elsewhere.
What Are the Physical Properties of Alloy 46?
For this grade the physical properties are the working data. The expansion coefficient, the Curie point and the density are the figures used in design; the mechanical table above is largely a formality.
| Property | Value | Design relevance |
|---|---|---|
| Density | 8.17 g/cm³ 0.295 lb/in³ | Use this figure for forging weight. See the weight calculator |
| Melting point | 1427 °C 2600 °F | Sets the forging and annealing windows |
| Curie (inflection) point | 460 °C 860 °F | The design limit. Above this the expansion match is lost |
| Mean CTE, 30–450 °C | 7.5 × 10⁻⁶ /°C | The property the alloy is specified for |
| Electrical resistivity, 20 °C | 47 µΩ·cm | Relevant to lead-in wires and resistance welding schedules |
| Thermal conductivity | 11 W/m·°C | Low, about a quarter of carbon steel. Affects sealing heat-up uniformity |
| Specific heat | 0.12 cal/g·°C ≈ 500 J/kg·°C | Used in sealing-cycle thermal calculations |
| Magnetic state at 20 °C | Ferromagnetic | Remains magnetic to 460 °C. Not a non-magnetic material |
Thermal Expansion of Alloy 46 and the 460 °C Curie Inflection
The table and chart below give the mean linear coefficient of thermal expansion measured from 30 °C to each upper temperature, per ASTM F30. The table gives the figures used in calculation; the chart shows the shape of the curve and why the figure changes after 460 °C.
| Temperature range | Mean CTE (× 10⁻⁶/°C) | Regime |
|---|---|---|
| 30 – 300 °C | 7.5 | Ferromagnetic, flat usable range |
| 30 – 400 °C | 7.1 – 7.8 | Ferromagnetic, flat usable range |
| 30 – 450 °C | 7.5 | Approaching the Curie point |
| 30 – 500 °C | 8.2 – 8.9 | Crosses 460 °C, curve is bending |
| 30 – 600 °C | 9.8 | Paramagnetic, match to soft glass lost |
| 30 – 700 °C | 10.7 | Paramagnetic |
| 30 – 800 °C | 11.6 | Paramagnetic |
| 30 – 900 °C | 12.5 | Paramagnetic |
| 30 – 1000 °C | 13.4 | Paramagnetic |
Values are typical for annealed material. Residual cold work distorts the coefficient, which is why controlled-expansion parts are used annealed. Where the coefficient is contractual, request dilatometer testing of the delivered heat.
Every figure in Table 5 is a mean coefficient from 30 °C to the stated upper temperature, not the instantaneous coefficient at that temperature. Total expansion is ΔL = CTE × L × ΔT. To compare two materials, both figures must be quoted over the same range. Comparing an alloy mean over 30–450 °C against a glass mean over 20–300 °C is a common seal-design error. The expansion calculator below does the arithmetic and flags the range mismatch.
📏 Alloy 46 expansion & mismatch calculator
Enter a dimension and a temperature excursion. Get the total movement of the Alloy 46 part, the movement of the mating material, and the differential that the seal or joint has to absorb.
Uses ASTM F30 mean coefficients for Alloy 46, interpolated between tabulated ranges and referenced to 30 °C. Mating-material values are nominal family figures for screening only. A seal design must use the dilatometer curve from the glass or ceramic manufacturer, because a matched seal depends on the whole expansion path up to the set point rather than on a single mean value.
How Does Alloy 46 Seal to Glass and Ceramic?
A glass-to-metal seal works because the metal and the glass shrink together on cooling from the sealing temperature. If the metal shrinks more than the glass, the glass ends in compression, which is usually acceptable and sometimes desirable. If the glass shrinks more, it ends in tension, and glass in tension cracks. Alloy 46 is used to keep that mismatch small and predictable from the glass set point down to room temperature.
Two kinds of seal exist and they are designed on opposite principles. A matched seal pairs a metal and glass with nearly identical expansion curves so that stress stays low throughout; this is the normal use for Alloy 46. A compression seal uses a metal with higher expansion in an outer ring, so that on cooling it squeezes an inner glass bead. It is used where hermeticity must survive shock and vibration. In a compression seal Alloy 46 is usually the inner pin, with a stainless or carbon-steel outer body.
| Glass / ceramic family | Nominal CTE (× 10⁻⁶/°C) | Fit with Alloy 46 | Better-matched grade |
|---|---|---|---|
| Soft lead glass | 8.9 – 9.2 | Workable, glass in slight compression | Alloy 48 is closer |
| Soda-lime glass | 8.5 – 9.5 | Workable, the standard soft-glass duty | Alloy 48 / Alloy 52 |
| 96 % alumina ceramic | 7.0 – 8.2 | Good match | Alloy 46 is the right choice |
| Aluminosilicate glass | 4.2 – 4.6 | Poor, glass would go into tension | Kovar |
| Hard sealing glass, 7052 / 7056 type | 4.6 – 5.2 | Poor | Kovar / Alloy 42 |
| Borosilicate (Pyrex 7740 type) | 3.2 – 3.4 | Unsuitable | Kovar |
| Fused silica | 0.5 – 0.6 | Unsuitable | No Fe-Ni match; use a graded seal |
Nominal family values for screening. Individual glass compositions vary widely within each family and the manufacturer's dilatometer curve always governs the final pairing.
🔬 Glass & ceramic seal compatibility checker
Pick the glass or ceramic you are sealing to and the seal type. Get a verdict on Alloy 46, the expansion mismatch, and the grade you should be using instead if this is not it.
Screening guidance based on nominal mean expansion values. A production seal must be qualified against the actual glass composition, the actual sealing cycle and a thermal-shock test programme. We supply the forging; the seal design remains the customer's responsibility.
🌡️ Service temperature & Curie point assessment
Enter service temperature, atmosphere and what the part has to do. Get a verdict, the governing mechanism, and where Alloy 46 runs out.
Screening guidance only. Alloy 46 is not a code pressure-vessel material and has no ASME allowable-stress tables. Long-term dimensional stability at temperature must be qualified by test on the actual heat.
Alloy 46 vs Invar 36, Alloy 42, Alloy 48, Alloy 52 and Kovar
Within the controlled-expansion family the choice comes down to expansion coefficient, and therefore to nickel content. The table below sets out the options.
| Grade | Nominal Ni | Mean CTE (× 10⁻⁶/°C) | Curie point | What it is for |
|---|---|---|---|---|
| Invar 36 | 36 % | 1.5 (20–100 °C) | 220 °C | Lowest expansion. Cryogenic, LNG containment, metrology, composite tooling, laser benches |
| Alloy 42 / Invar 42 | 42 % | 5.3 (20–300 °C) | 370 °C | Semiconductor lead frames, thermostat rods, bimetal, some hard-glass sealing |
| Kovar / Alloy K | 29 % Ni + 17 % Co | 5.3 (20–450 °C) | 450 °C | Borosilicate hard glass and alumina ceramic seals. Fe-Ni-Co, not binary |
| Alloy 46 | 46 % | 7.5 (30–450 °C) | 460 °C | Soft lead and soda-lime glass seals, alumina ceramic, hermetic packages |
| Alloy 48 | 48 % | 8.5–8.9 (20–450 °C) | 460 °C | Soft glass seals with a closer match than 46; industrial thermostats to 450 °C |
| Alloy 52 | ≈ 50–52 % | ≈ 9.5–10.2 | ≈ 500 °C | Highest-expansion Fe-Ni sealing grade; soda-lime glass and some ceramics |
Temperature ranges differ between published sources (30– versus 20–). Always compare two grades on the same range before finalising a design. Alloy 52 values are approximate and should be confirmed against the specific supplier's data.
You need the flat range to reach 460 °C
The Alloy 42 curve starts bending at 370 °C. Where the sealing or service cycle goes above that, Alloy 46 or 48 holds its coefficient and Alloy 42 does not.
The glass is soda-lime and the seal is critical
At 8.5–8.9 Alloy 48 sits closer to the 8.5–9.5 of soda-lime glass than the 7.5 of Alloy 46. On a demanding matched seal that difference is worth having.
The glass is borosilicate or hard
No binary Fe-Ni grade reaches down to 3.3. Hard-glass work requires the Fe-Ni-Co chemistry of Kovar; adjusting nickel does not get there.
You need dimensional stability, not a glass match
Tooling, metrology, cryogenic and LNG work need the lowest expansion below 220 °C. Invar 36 covers that; Alloy 46 expands roughly five times as much.
🔄 Controlled-expansion grade selector: is Alloy 46 the right grade?
Describe the duty. The tool returns the grade that fits and the reason, including when that grade is not Alloy 46.
A screening recommendation, not a design. We forge every grade named here, so the result is not weighted towards Alloy 46. Where the duty needs Invar 36 or Kovar, the tool returns that.
Alloy 46 Failure Modes and How to Design Them Out
Alloy 46 rarely fails mechanically. Failures usually come from something in the specification, the processing chain or the service cycle that has changed the expansion behaviour. These are the eight most common cases.
1. Residual cold work left in the part
The most common cause of an out-of-spec expansion coefficient. Machining, straightening, forming or a skipped anneal all leave strain that shifts the coefficient. Design it out: specify the delivery condition as annealed, and anneal again after any heavy machining or forming. Never accept a controlled-expansion part in the as-forged condition.
2. Service above the 460 °C Curie point
The seal was designed on the 7.5 coefficient and the process runs at 550 °C, where the effective coefficient is nearer 8.5–9. The mismatch grows, the glass goes into tension and the seal cracks, often on the second or third thermal cycle rather than the first. Design it out: check the maximum temperature of the sealing cycle as well as of service; the sealing cycle is usually the hotter of the two.
3. Comparing coefficients over different temperature ranges
Glass data is often quoted 20–300 °C, alloy data 30–450 °C. Comparing the two numbers directly can hide a mismatch of a full unit. Design it out: convert both to the same range, or better, overlay the two dilatometer curves.
4. Carbon at the sealing surface
Residual carbon reacts with the surface oxide during sealing and evolves CO, which shows up as bubbles at the interface and destroys hermeticity. Design it out: decarburise in wet hydrogen before sealing, and keep machining coolant residues off the sealing face.
5. Wrong oxide, or no oxide
A matched seal needs a thin, adherent, controlled oxide for the glass to key into. With too little the glass does not wet; with too much the oxide layer becomes the weak plane. Design it out: use a controlled oxidation cycle and specify the oxide colour or thickness on the drawing. The surface preparation tool gives a starting recipe.
6. Assuming the part is non-magnetic
Alloy 46 is ferromagnetic to 460 °C. Designers moving across from austenitic stainless sometimes assume any nickel alloy is non-magnetic, then find the part disturbing a nearby sensor or holding swarf. Design it out: treat it as a magnetic material throughout, in fixturing, in cleaning and in the final assembly.
7. Corrosion in storage and handling
No chromium means no passive film. Finished sealing faces will rust in a humid warehouse in weeks. Design it out: specify oiling or VCI packaging on the order, and plate or seal parts promptly after machining.
8. Sulfur pick-up during heating
Like other high-nickel materials, Fe-Ni alloys are embrittled by sulfur at temperature. A sulfur-bearing furnace atmosphere, a marking crayon or a grease residue is enough to cause intergranular cracking during forging or annealing. Design it out: clean parts before any thermal cycle and use sulfur-free furnace fuel and protective atmospheres.
How Do You Forge, Anneal, Machine and Weld Alloy 46?
Forging practice
Alloy 46 forges readily and behaves much like an austenitic stainless: no phase transformation to work around, good ductility and a wide working range. Two points require control. The first is sulfur cleanliness; parts and tooling must be free of sulfur-bearing lubricants before heating. The second is forging ratio. The cast structure must be fully broken down, because coring and segregation carried over from the ingot produce local variations in nickel content and therefore local variations in expansion coefficient across a single part.
Melting route
We melt Alloy 46 by EAF + VOD followed by electroslag remelting (ESR). ESR matters more for this grade than for a structural steel. Nickel segregation of a few tenths of a percent is of little consequence in structural work but not here: it moves the local Curie point and the local expansion curve, producing a part whose seal behaves differently in different places. ESR provides the chemical homogeneity a controlled-expansion part depends on.
Heat treatment
There are two thermal treatments, and neither of them hardens the material.
- Annealing, 850 to 1000 °C in a protective atmosphere, slow cool. Restores the published expansion curve after forging or machining. This is the standard delivery condition and the condition in which the alloy must be used where dimensional stability matters.
- Stress relief, typically 650 to 750 °C after heavy machining. Removes machining stress without a full recrystallisation cycle, for cases where a full anneal would distort a finish-machined part.
Protective atmospheres (dry hydrogen, cracked ammonia, argon or vacuum) are used to avoid scaling and to avoid picking up sulfur. Air annealing is acceptable for rough stock that will be machined all over, but not for finished sealing surfaces.
🧪 Sealing surface preparation advisor
Surface condition governs glass-to-metal sealing. Describe the seal to get a starting preparation route: decarburise, oxidise, plate, or a combination.
A starting point based on established practice for iron-nickel sealing alloys. Oxide thickness, decarburising time and plating specification must be qualified on your own parts against your own sealing cycle.
🔥 Alloy 46 anneal & stress-relief recipe generator
Enter section thickness and the condition the part is in. Get a soak temperature, a soak time, an atmosphere and a cooling instruction you can put straight on a route card.
Recipes follow published practice for iron-nickel controlled-expansion alloys (anneal 850–1000 °C, protective atmosphere, slow cool). Times are rule-of-thumb soak times at temperature and exclude ramp. Qualify on your own parts before production release.
Machining
Alloy 46 machines like a soft austenitic material: it work hardens, it builds up on the cutting edge and it produces long stringy chips. Machine in the annealed condition with high-speed steel or carbide, positive rake, sharp edges, rigid setups and generous coolant. Take a positive cut, since light dwelling passes glaze and harden the surface. Sealing components need an anneal or stress relief after machining to restore the expansion coefficient.
🔧 Alloy 46 machinability parameter calculator
Choose the operation and tool, enter the diameter. Get cutting speed, spindle speed, feed and depth of cut in the published range for iron-nickel controlled-expansion alloys.
Starting parameters derived from published feeds and speeds for NILO-type iron-nickel alloys. Cutting fluid: straight cutting oil, EP medium duty, or soluble oil at 20:1 for turning, drilling and milling. Adjust for your machine, tooling and coolant.
Welding
Alloy 46 is weldable by TIG, plasma, electron beam, laser and resistance methods, subject to one restriction: a weld is a locally cast structure with a locally different expansion coefficient. On a structural joint this does not matter. On a sealing surface it does, and welds should be kept away from seal faces or removed by machining. MIG spray transfer and submerged arc are not recommended for this alloy family. Post-weld annealing restores the expansion behaviour of the heat-affected zone where the geometry allows it.
Alloy 46 Production Capability at Jiangyin Jiangnan Metal
Process flow for every UNS K94600 order
- Enquiry reviewDrawing checked for grade, condition and expansion requirement. Specification errors queried before quoting
- MeltingEAF + VOD, then ESR remelt for chemical homogeneity
- Ingot inspectionChemistry verified top and bottom; ingot conditioned
- ForgingOpen-die forging or seamless ring rolling to a controlled forging ratio
- Annealing850–1000 °C, protective atmosphere, slow cool. Restores the expansion curve
- MachiningAs-forged, rough-machined or finish-machined to print
- TestingUT, chemistry, mechanicals, grain size, dimensions; dilatometer on request
- Certification & despatchEN 10204 3.1 or 3.2, VCI or oiled packing, export crating
| Form | Capability | Typical Alloy 46 order |
|---|---|---|
| Seamless rolled rings, OD | 200 – 2,500 mm | 250 – 600 mm |
| Discs, blanks and tube sheets | to 1,800 mm diameter | 150 – 500 mm |
| Forged round bar | 25 – 500 mm Ø | 40 – 200 mm Ø |
| Shafts and spindles, length | to 8,000 mm | to 1,500 mm |
| Single-piece weight | to 15,000 kg | 5 – 400 kg |
| Minimum order | Single pieces accepted. Open-die forging needs no dies, so there is no tooling cost to amortise | |
| Typical lead time | 6 – 10 weeks from order confirmation, depending on melt scheduling and machining scope | |
Capability figures cover the full nickel-alloy range of the works. Alloy 46 orders sit at the small end of that envelope; the right-hand column shows the sizes most often shipped in this grade.
Equipment used for Alloy 46
- Hydraulic open-die presses with manipulators for bars, blocks, discs and shafts
- Radial-axial ring rolling mills for seamless rings from 200 to 2,500 mm OD
- Electroslag remelting furnaces for homogeneity-critical grades
- Atmosphere-controlled and vacuum heat treatment furnaces with calibrated recording
- CNC vertical and horizontal lathes, boring mills and drilling machines for tube sheets
- Ultrasonic testing to EN 10228-3, SEP 1921 and ASTM A388; spectrometer; mechanical test laboratory
⚖️ Alloy 46 forging weight calculator
Alloy 46 is priced by weight. Enter the finished geometry and get the net weight, plus an estimated forging weight including machining allowance.
Calculated at a density of 8.17 g/cm³. Forging weight is an estimate for budgeting; the actual input weight depends on the forging route, the ingot size available and the test-piece allowance, and is confirmed at quotation.
Which Standards, Testing and Certification Apply to Alloy 46 Forgings?
| Area | Standard | What it covers |
|---|---|---|
| Material | ASTM F30 | Iron-nickel sealing alloys: chemistry and general requirements |
| Material (defence) | AMS I-23011 Cl. 4 · MIL-I-23011 Cl. 4 | Class 4 covers the 46 % Ni composition |
| Material (China) | GB 4J46 | Chinese controlled-expansion designation |
| Ultrasonic testing | EN 10228-3 · SEP 1921 · ASTM A388 | Volumetric soundness; acceptance class stated on the order |
| Certification | EN 10204 3.1 | Standard. Mill certificate with actual test results |
| Certification (witnessed) | EN 10204 3.2 | Third-party witness (TÜV, BV, SGS, Lloyd's) on request |
| Expansion verification | Dilatometry on delivered heat | Optional. Specify the temperature range and tolerance on the order |
| Quality system | ISO 9001:2015 | Works quality management system |
A standard EN 10204 3.1 certificate reports chemistry and mechanical properties. It does not report the expansion coefficient, because ASTM F30 does not require it as a routine test. Where the design depends on a specific coefficient over a specific range, as a sealing part does, state it on the purchase order. We will then run dilatometry on the delivered heat and report it on the certificate. The cost at order stage is small; discovering the problem after delivery is not.
Where Is Alloy 46 Used? Applications by Industry
Glass-to-metal seals
Electronic tubes, hermetic packages, headers and feedthroughs sealed to soft lead and soda-lime glass. The principal use of the alloy.
Lamps and vacuum devices
Lead-in wires, eyelets, header rings and envelope components in lamp and vacuum-device manufacture.
Packages, covers, frames
Housings, lids, spacers and specialised frames where the package must stay dimensionally matched to its ceramic or glass.
Ceramic-to-metal assemblies
Alumina ceramic joints where the ceramic expansion falls in the 7–8 range, one of the closer matches for this grade.
Thermostatic bimetal
The low-expansion leg of bimetal strip and thermostat elements operating within the flat range.
Precision & metrology parts
Resonator bodies, dimensionally stable fixtures and instrument components where a predictable, repeatable coefficient matters more than a low one.
Some supplier listings, including an earlier version of this page, show Alloy 46 for LNG tanks, cryogenic transfer lines, valve bodies and general offshore hardware. Those applications are wrong and have been removed. LNG and cryogenic containment require Invar 36, whose expansion is about five times lower. Corrosion-service valve bodies require a chromium- or nickel-bearing corrosion alloy, since Alloy 46 has no corrosion resistance. We will say so at enquiry stage rather than ship a grade that cannot do the job.
How to Specify and Order an Alloy 46 Forging
Seven items of information are needed to turn an enquiry into a firm price and a correct part.
- State the grade unambiguouslyWrite UNS K94600 or ASTM F30 Alloy 46. Generic designations avoid trademark and interpretation problems
- Give the geometryOD × ID × height for rings, Ø × length for bars, or send the drawing
- State the conditionAs-forged, rough-machined or finish-machined, and always annealed
- State the expansion requirementMating glass or ceramic, temperature range, and whether dilatometry is required
- Define testingUT standard and acceptance class; mechanical and grain-size requirements
- Define certificationEN 10204 3.1, or 3.2 with a named third party
- State surface requirementsDecarburising, oxidation, plating, and protective packing for storage
Ten Mistakes Engineers Make When Ordering Alloy 46
| # | Mistake | Consequence | Fix |
|---|---|---|---|
| 1 | Specifying a hardened or aged condition | Not possible; the alloy has no age-hardening mechanism | Specify annealed; carry the load elsewhere in the design |
| 2 | Omitting the annealed delivery condition | Residual cold work distorts the expansion coefficient | Write "annealed" on the drawing, every time |
| 3 | Designing a cycle that goes above 460 °C | Coefficient rises; glass goes into tension and cracks | Check the sealing cycle temperature, not just service |
| 4 | Comparing CTE over mismatched ranges | Hidden mismatch of up to a full unit | Convert both figures to the same range before comparing |
| 5 | Assuming Alloy 46 resists corrosion | Rust on sealing faces within weeks in humid storage | Specify VCI or oiled packing; plate or seal promptly |
| 6 | Assuming it is non-magnetic | Sensor interference, swarf retention, fixturing problems | Treat as ferromagnetic up to 460 °C throughout |
| 7 | Ordering by trade name only | Trademark and sourcing ambiguity; possible wrong grade | Order to UNS K94600 / ASTM F30 |
| 8 | Expecting CTE on a standard 3.1 certificate | ASTM F30 does not require it; you will not receive it | Request dilatometry explicitly on the purchase order |
| 9 | Confusing Alloy 46 with Invar 36 or Alloy 42 | Expansion off by a factor of up to five | Check the nickel content on the certificate, not the name |
| 10 | Welding across a sealing surface | Weld metal has a different local coefficient; the seal fails | Keep welds away from seal faces or machine them out |
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Drawing Callout Template for Alloy 46
Copying this block onto the drawing or into the purchase order removes most of the usual queries.
| Line | Callout |
|---|---|
| Material | Alloy 46, UNS K94600, to ASTM F30 |
| Product form | Open-die forging / seamless rolled ring |
| Melt route | EAF + VOD + ESR |
| Condition | Annealed 850–1000 °C, protective atmosphere, slow cool |
| Expansion requirement | Mean CTE 7.5 × 10⁻⁶/°C over 30–450 °C; verify by dilatometry on delivered heat; report on certificate |
| NDT | Ultrasonic test to EN 10228-3, quality class [state class] |
| Certification | EN 10204 3.1 [or 3.2, witness: state body] |
| Surface | [Decarburised / controlled oxide / plated: state requirement]. No welds on sealing surfaces |
| Marking | Heat number, grade, drawing number, low-stress stamps only |
| Packing | VCI or oiled, sealed, export crate. Material has no corrosion resistance |
Glossary of Alloy 46 Terms
- Controlled-expansion alloy
- An alloy formulated so that its thermal expansion matches a mating material rather than being as low as possible.
- Curie point
- The temperature at which a ferromagnetic material becomes paramagnetic. For Alloy 46 this is 460 °C, which is also the inflection point of its expansion curve.
- Inflection point
- The temperature at which the expansion curve changes slope. In Fe-Ni alloys it coincides with the Curie point.
- Invar effect
- The near-cancellation of thermal expansion by magnetostriction in ferromagnetic Fe-Ni alloys, discovered by Guillaume in 1896.
- Matched seal
- A glass-to-metal seal in which metal and glass have nearly identical expansion curves, so residual stress stays low.
- Compression seal
- A seal in which an outer metal of higher expansion shrinks onto an inner glass bead, holding it in compression.
- Set point
- The temperature below which a cooling glass behaves as a rigid solid and stress begins to accumulate in the seal.
- Dilatometry
- Direct measurement of specimen length against temperature. The only way to verify an expansion coefficient on a delivered heat.
- Decarburising
- Removing surface carbon, normally in wet hydrogen, so that no CO evolves during glass sealing.
- ESR
- Electroslag remelting. A secondary melting route that refines structure and improves chemical homogeneity.
- Hermeticity
- The leak-tightness of a sealed package, usually specified as a maximum helium leak rate.
- EN 10204 3.1 / 3.2
- Material certificate types. 3.1 is issued by the manufacturer's own inspection function; 3.2 is countersigned by an independent third party.
Frequently Asked Questions on Alloy 46 / UNS K94600
What is Alloy 46?
Alloy 46 is a controlled-expansion iron-nickel alloy containing a nominal 46 % nickel with the balance iron. It is specified under UNS K94600 and ASTM F30 and is also sold as Nilo® 46, Pernifer® 46, Glass Sealing 46, Invar 46 and 4J46. Its mean coefficient of thermal expansion of about 7.5 × 10−6/°C is matched to soft lead and soda-lime glasses, which makes it a standard choice for glass-to-metal seals in electronic tubes, lamps and hermetic packages.
What is the thermal expansion coefficient of Alloy 46?
About 7.5 × 10−6/°C over 30–300 °C and again over 30–450 °C, per ASTM F30 data. Above the Curie point of 460 °C the alloy loses ferromagnetic ordering and expansion rises steeply: roughly 9.8 × 10−6/°C over 30–600 °C, 11.6 over 30–800 °C and 13.4 over 30–1000 °C. The full table is in Table 5.
What is the Curie point of Alloy 46 and why does it matter?
About 460 °C (860 °F). It is also the inflection point of the expansion curve, which is why it governs the design. Below it the alloy holds a low, nominally constant coefficient; above it the coefficient rises and the match to soft glass is lost. A seal design must stay below the inflection point, including during the sealing cycle itself, which is often hotter than service.
Is Alloy 46 magnetic?
Yes. Alloy 46 is ferromagnetic at room temperature and remains magnetic up to about 460 °C, becoming paramagnetic above that. The magnetic transition and the expansion behaviour are the same physical phenomenon, so they cannot be separated: any Fe-Ni alloy with a useful flat expansion range is necessarily magnetic within that range.
What is the difference between Alloy 46, Alloy 42, Alloy 48 and Invar 36?
Nickel content sets the expansion coefficient. Invar 36 (36 % Ni) has the lowest expansion, near 1.5 × 10−6/°C at room temperature, and is used for cryogenic and dimensional-stability work. Alloy 42 (42 % Ni) runs about 5.3, Alloy 46 about 7.5, Alloy 48 about 8.5–8.9 and Alloy 52 about 9.5–10.2. Alloy 46 and 48 are the soft-glass sealing grades; Kovar, an Fe-Ni-Co alloy, is used for hard borosilicate glass. The full comparison is in Table 7.
Can Alloy 46 be hardened by heat treatment?
No. It is a single-phase binary solid solution with no γ′-forming elements, so no thermal cycle raises its strength. Strength comes only from cold work, which a controlled-expansion part must not retain, because residual strain distorts the expansion coefficient. A drawing calling for solution treatment and ageing has usually been copied from a different alloy and should be queried.
Why must Alloy 46 forgings be supplied annealed?
Because residual cold work distorts the coefficient of thermal expansion. A part forged or machined without a subsequent anneal will not follow the published curve, and a glass seal designed against that curve can crack on cooling or after a few thermal cycles. Annealing is carried out at 850–1000 °C in a protective atmosphere with slow cooling.
Does Alloy 46 resist corrosion?
No. It contains at most 0.25 % chromium as a residual, so there is no passive film and no meaningful corrosion resistance. It rusts in damp air much like a plain carbon steel. Sealing components are normally plated, oxidised or hermetically enclosed. Specify VCI or oiled packing for storage and transport, and protect machined sealing faces immediately.
Which glasses can Alloy 46 be sealed to?
Soft glasses, meaning soft lead glass and soda-lime glass, and some alumina ceramics, whose expansion in the 7–8 range is the closest match of all. It is not suitable for borosilicate or other hard glasses near 3.3 × 10−6/°C; those require Kovar. A matched seal depends on the whole expansion path up to the glass set point rather than one mean value, so verify the pairing against the dilatometer curve from the glass manufacturer. The seal compatibility checker screens this quickly.
What forged shapes can be made in Alloy 46?
Seamless rolled rings, forged rings, flanges, round and flat bar, discs and blanks, shafts and spindles, sleeves, bushings, hollow bar, tube sheets and forged blocks, all made to the customer's drawing. Open-die forging needs no dies, so single prototype pieces carry no tooling cost and are accepted alongside production quantities.
What testing and certification comes with Alloy 46 forgings?
Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388 as the order requires. Certificates are issued to EN 10204 3.1 as standard, with 3.2 third-party witnessed certification available on request. Chemical analysis, mechanical test, grain size and dimensional inspection reports are included. Dilatometer testing of the delivered heat is available and should be requested explicitly, because ASTM F30 does not require it as a routine test.
How is Alloy 46 melted before forging?
EAF plus VOD, followed by electroslag remelting. ESR matters more here than for structural steels: local segregation of nickel by a few tenths of a percent shifts the local Curie point and therefore the local expansion coefficient, giving a part whose seal behaves differently in different places. ESR provides the chemical homogeneity a controlled-expansion part depends on.
Is Nilo 46 the same as Alloy 46?
Yes, the same 46 % nickel iron-nickel chemistry. Nilo® is a registered trademark of Special Metals Corporation, Pernifer® of VDM Metals and CarTech® Glass Sealing 46 of Carpenter Technology. Jiangyin Jiangnan Metal is not affiliated with any of them. We ship the generic equivalent, UNS K94600 to ASTM F30, with a certificate listing every specification the heat satisfies.
Where can I buy Alloy 46 forgings?
Alloy 46 forgings are supplied worldwide by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Email sales@steelforgepieces.com or call +86-189-2135-9659 with a drawing or the required dimensions, quantity and specification. A firm price and lead time is normally returned within 24 hours.
Technical References
- ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys. Chemistry, product forms and the thermal expansion data in Table 5.
- AMS I-23011 / MIL-I-23011, Iron-Nickel Alloys for Sealing and Magnetic Applications, Class 4.
- Special Metals Corporation, NILO® and NILOMAG® Nickel-Iron Alloys, publication SMC-031. Comparative expansion, heat treatment, machining and welding practice for the Fe-Ni family.
- Published mill datasheets for Alloy 46 / UNS K94600. Density, Curie point, resistivity, thermal conductivity and specific heat.
- C.-É. Guillaume, original work on Fe-Ni Invar alloys, 1896.
- EN 10204, Metallic products: types of inspection documents.
- EN 10228-3 / SEP 1921 / ASTM A388, ultrasonic examination of forgings.
Property values on this page are typical figures for annealed material, compiled from the sources above for engineering guidance. They are not a specification and do not replace the material test certificate for a given heat.
Request an Alloy 46 / UNS K94600 Forging Quotation
Send a drawing or the dimensions, the quantity and the specification. We reply with a firm price, a lead time and any specification queries, normally within 24 hours and always before production starts.
Single prototype pieces are accepted. Open-die forging needs no dies, so there is no tooling cost to spread across a batch.
Open-Die Forging Factory
Related Nickel Alloy Forging Grades
Invar 36
36 % Ni. The lowest-expansion grade, for cryogenic, LNG, metrology and composite tooling.
Invar 42 / Alloy 42
42 % Ni, CTE ≈ 5.3. Lead frames, thermostat rods, bimetal strip.
Alloy 48
48 % Ni, CTE ≈ 8.5–8.9. The closer match to soda-lime glass.
Alloy 52
≈ 50–52 % Ni. The highest-expansion Fe-Ni sealing grade.
NI-SPAN-C Alloy 902
Controlled elastic modulus rather than controlled expansion, and unlike Alloy 46 it is age hardenable.
Alloy 400 / Monel 400
Ni-Cu. Seawater, hydrofluoric acid and caustic service, where corrosion resistance is the requirement.
Inconel 718
Age-hardenable Ni-Cr superalloy for high-temperature strength.
All nickel alloy grades
The full range of nickel-alloy forgings we produce.
Page last reviewed 12 August 2026 by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team. Technical data is given for guidance and does not replace the material test certificate for a specific heat.