---
title: "NILO K Forgings: ASTM F-15 Rings, Bars, Discs (UNS K94610)"
description: "Open-die forged NILO alloy K to ASTM F-15 / UNS K94610. 29Ni-17Co-Fe, CTE 5.5 ppm/K, Curie 435 °C. Composition, properties, forged forms. Quote in 24 h."
canonical: https://www.steelforgepieces.com/Nickel-Alloy/NILO-K.html
author: "Jiangyin Jiangnan Metal Co., Ltd., Metallurgical Engineering Team"
updated: 2026-08-25
grade: NILO alloy K
uns: K94610
astm: F-15
werkstoff: "1.3981 (NiCo 29 18)"
---

# NILO K Forgings: ASTM F-15 / UNS K94610 Glass-Sealing Alloy

UNS K94610 · ASTM F-15 · W.Nr. 1.3981 · NiCo 29 18 · Kovar · Pernifer 2918 · Rodar · Dilver P1 · Nicosel

NILO alloy K is a controlled-expansion sealing alloy containing about **29 % nickel, 17 % cobalt and the balance iron**. It is specified to **ASTM F-15** and numbered **UNS K94610**. Its mean coefficient of thermal expansion is about **5.5 × 10⁻⁶/K between 30 °C and 200 °C**, close enough to hard borosilicate glass and high-alumina ceramic that a hermetic seal survives repeated heating and cooling without cracking. NILO K is used for glass-to-metal seals in vacuum tubes, transistor headers, microwave devices and hermetic electronic packages.

**Jiangyin Jiangnan Metal Co., Ltd.** forges NILO K to customer drawings at its open-die plant in Jiangyin, Jiangsu Province, China. Forms include seamless rolled rings, forged rings, round bar, discs, flanges, sleeves, bushings, tube sheets, hollow bar and shafts. Material is melted by **EAF + VOD + ESR** and supplied annealed at 850–1000 °C in dry hydrogen or cracked ammonia. Ultrasonic examination is to **ASTM A388** or **EN 10228-3**, and certification is **EN 10204 3.1** as standard with 3.2 third-party witness on request. Quality management is certified to **ISO 9001:2015**. Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Quotations are issued within 24 hours from sales@steelforgepieces.com or 0086-189-2135-9659.

| Key figure | Value |
| --- | --- |
| Nickel, nominal | 29 % |
| Cobalt, nominal, balance iron | 17 % |
| Mean CTE 30–200 °C | 5.5 × 10⁻⁶/K |
| Curie point | 435 °C |
| Density | 8.36 g/cm³ |
| Certificate | EN 10204 3.1 / 3.2 |

Grade datasheet · 1 of 72 nickel and controlled-expansion grades · Last updated 25 August 2026 · Maintained by the Jiangyin Jiangnan Metal metallurgical engineering team

**NILO K and Kovar are the same specification.** Both names describe the iron-nickel-cobalt sealing alloy covered by ASTM F-15 and numbered UNS K94610. NILO is a Special Metals Corporation trade name and Kovar a CRS Holdings trade name. If your drawing carries the other name, our [Kovar datasheet](https://www.steelforgepieces.com/Nickel-Alloy/Kovar.html) holds the same technical data.

## What is the chemical composition of NILO K?

The chemistry below is the ASTM F-15 specification we melt to. Nickel and cobalt are held to a narrow band because the expansion match to glass depends on them directly, and a point or two of nickel is enough to move the curve and break a seal. Residual elements are capped so the alloy oxidises evenly and machines predictably.

*Table 1. NILO K chemical composition to ASTM F-15, weight % (Fe = balance)*

| Element | Content % | Basis | Why it is controlled |
| --- | --- | --- | --- |
| Nickel (Ni) | 29.0 | Nominal | Sets the expansion curve together with cobalt |
| Cobalt (Co) | 17.0 | Nominal | Raises the Curie temperature so the flat part of the curve extends past 400 °C |
| Iron (Fe) | 53.0 | Balance | Base element |
| Carbon (C) | 0.04 | Max | Carbon evolves as gas during sealing and leaves bubbles in the joint |
| Manganese (Mn) | 0.50 | Max | Deoxidiser, combines with sulfur |
| Silicon (Si) | 0.20 | Max | Residual limit, affects glass wetting |
| Aluminium (Al) | 0.10 | Max | Residual limit, forms a refractory oxide that hinders sealing |
| Chromium (Cr) | 0.20 | Max | Residual limit, chromium oxide interferes with the sealing film |
| Magnesium (Mg) | 0.10 | Max | Residual limit |
| Zirconium (Zr) | 0.10 | Max | Residual limit |
| Titanium (Ti) | 0.10 | Max | Residual limit |
| Copper (Cu) | 0.20 | Max | Residual limit |
| Molybdenum (Mo) | 0.20 | Max | Residual limit |

Typical published chemistry for the alloy, not a guarantee for a specific heat. The analysis of your material is certified heat by heat on the EN 10204 inspection certificate issued with the order.

## What are the mechanical and physical properties of NILO K?

### Mechanical, annealed, at 20 °C

*Table 2. NILO K mechanical properties*

| Property | Metric | Imperial |
| --- | --- | --- |
| Tensile strength | min 520 MPa | min 75 ksi |
| Yield strength, 0.2 % | min 340 MPa | min 49 ksi |
| Elongation, 4D | min 42 % | min 42 % |
| Modulus of elasticity | ≈ 138 GPa | ≈ 20 × 10⁶ psi |
| Hardness | ≈ 150 HV | ≈ 80 HRB |

### Physical, at 20 °C unless stated

*Table 3. NILO K physical properties*

| Property | Value |
| --- | --- |
| Density | 8.36 g/cm³ |
| Melting point | ≈ 1450 °C |
| Curie temperature | ≈ 435 °C |
| Thermal conductivity | ≈ 17.3 W/m·K |
| Specific heat | ≈ 439 J/kg·K |
| Electrical resistivity | ≈ 49 µΩ·cm |
| Magnetic state | Ferromagnetic below 435 °C |

Typical published values, given for design screening. The mill test certificate issued with each forging governs acceptance.

## Why does NILO K seal to glass?

NILO K is specified for its expansion behaviour rather than for strength. Between room temperature and about 450 °C the alloy expands very little and follows hard borosilicate glass closely enough that a seal cools without cracking. Above an inflection point near 450 °C, which sits just above the Curie temperature of about 435 °C, expansion rises steeply and the match to glass is lost. That inflection point sets the practical ceiling for sealing service. Oxidation resistance is not the limiting factor.

*Table 4. NILO K mean coefficient of thermal expansion, measured from 30 °C*

| Temperature range | Mean CTE (10⁻⁶/K) | Behaviour |
| --- | --- | --- |
| 30–200 °C | 5.5 | Nominal sealing range, matched to hard borosilicate glass |
| 30–300 °C | 5.1 | Still within the sealing match |
| 30–400 °C | 4.9 | Minimum of the curve |
| 30–450 °C | 5.2 | Inflection point, match begins to break down |
| 30–500 °C | 6.2 | Above the Curie point, expansion rising |
| 30–600 °C | 7.6 | Outside any useful controlled-expansion range |

Typical published values. Expansion varies with heat treatment, section size and measurement method. Where the coefficient is contractual, ask for a push-rod dilatometry result to ASTM E228 on the certificate rather than relying on a published table.

**Selection note.** [Invar 36](https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html) has the lowest expansion of any commercial metal at about 1.2 × 10⁻⁶/K, and is used where a part must hold its dimensions. NILO K expands roughly four and a half times faster because it has to follow the glass it is sealed to. Specifying NILO K where dimensional stability is wanted, or Invar where a glass seal is wanted, is a common error in this alloy family.

### How NILO K compares with the other iron-nickel sealing alloys

*Table 5. Controlled-expansion alloy family, approximate expansion and what each is matched to*

| Grade | Nominal composition | Approx. CTE (10⁻⁶/K) | Matched to / used for |
| --- | --- | --- | --- |
| [Invar 36](https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html) | 36 Ni · bal. Fe | ≈ 1.2 | Dimensional stability: metrology frames, composite tooling, cryogenic structures |
| NILO K | 29 Ni · 17 Co · bal. Fe | ≈ 5.5 | Hard borosilicate glass (7052 / 7040 type) and alumina ceramic seals |
| [Alloy 42 / Invar 42](https://www.steelforgepieces.com/Nickel-Alloy/Invar-42.html) | 42 Ni · bal. Fe | ≈ 4.5–5.3 | Lead frames, semiconductor packages, sealing to some hard glasses |
| [Alloy 42-6](https://www.steelforgepieces.com/Nickel-Alloy/Alloy-42-6.html) | 42 Ni · 6 Cr · bal. Fe | ≈ 5.5–6.5 | Chromium added for oxide adherence in sealing service |
| [Alloy 45](https://www.steelforgepieces.com/Nickel-Alloy/Alloy-45.html) | 45 Ni · bal. Fe | ≈ 6.5–7.2 | Intermediate-expansion glass seals |
| [Alloy 46](https://www.steelforgepieces.com/Nickel-Alloy/Alloy-46.html) | 46 Ni · bal. Fe | ≈ 7.3–7.7 | Intermediate-expansion glass seals |
| [Alloy 48](https://www.steelforgepieces.com/Nickel-Alloy/Alloy-48.html) | 48 Ni · bal. Fe | ≈ 8.6–9.2 | Soft soda-lime glass seals |
| [Alloy 52](https://www.steelforgepieces.com/Nickel-Alloy/Alloy-52.html) | 51 Ni · bal. Fe | ≈ 9.6–10.2 | Soft glass seals, lamp and tube components |

Approximate values published for the alloy family, given for selection guidance only. Measurement ranges differ between sources, so compare against one dataset rather than mixing them, and confirm against a dilatometry result before committing a seal design.

## Which forged product forms are available in NILO K?

NILO K parts are made to order against a drawing rather than supplied from stock. Ring rolling covers seal rings, housings and flanged bodies. Open-die forging covers bar, discs, blocks and shafts. Trepanning produces hollow bar for tubular bodies and cavity resonators. NILO K costs many times more per kilogram than steel and cuts slowly, so near-net-shape forging usually repays its tooling cost. State at enquiry stage whether you want as-forged stock, a rough-machined proof shape, or finish machining to drawing.

- [Seamless rolled rings](https://www.steelforgepieces.com/Seamless-Rolled-Rings/Seamless-Rolled-Ring.html): ring-rolled, no weld seam, rectangular or profiled section
- [Forged rings](https://www.steelforgepieces.com/Forging-Rings/Forging-Ring.html): upset and punched, for smaller diameters and heavy walls
- [Forged flanges](https://www.steelforgepieces.com/Forged-Flanges/Forged-Flange.html): vacuum flanges, feedthrough bodies, blind and weld-neck patterns
- [Forged discs and blanks](https://www.steelforgepieces.com/Forged-Disks/Forged-Disk.html): upset forged for covers, headers and machining blanks
- [Round bar and shafts](https://www.steelforgepieces.com/Forging-Products/Forging-Steel-Products.html): forged and peeled or rough turned, cut to length
- [Sleeves and cylinders](https://www.steelforgepieces.com/Forged-Cylinders/Forged-Cylinder.html): trepanned or bored, thin and heavy wall
- [Forged bushings](https://www.steelforgepieces.com/Forged-Bushing/Forged-Bushings.html): hollow forged to drawing
- Tube sheets: forged and drilled tube sheets and feedthrough plates
- Hollow bar: trepanned hollows for tubular bodies and cavity resonators
- [Custom forged pieces](https://www.steelforgepieces.com/Forging-Pieces/Forging-Piece.html): near-net-shape bodies, blocks, nozzles and stems to drawing

**Size note.** The plant envelope given below is our general open-die capability across the carbon, alloy and nickel grades. NILO K is normally ordered in much smaller sections than the plant maximum, and very large NILO K forgings are rarely economic. Send the drawing and we will say whether the geometry suits this alloy or whether another grade would serve better.

## What can Jiangyin Jiangnan Metal forge in NILO K?

### Forging and ring rolling

1 t, 3 t, 5 t and 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses, and radial-axial ring mills to 2,500 mm outside diameter on a 6 m ring line. NILO K has a narrow hot-working window and work-hardens quickly, so forging is planned in incremental passes with a controlled finish temperature and a reduction of at least 4:1 to break down the cast structure. An under-worked forging will not give a consistent expansion coefficient through section.

### Melting route

Material is bought against your specification and melted by EAF + VOD + ESR. Electroslag remelting gives the cleanliness and structural uniformity a hermetic seal needs, since an inclusion at the sealing surface becomes a leak path. Heat numbers are traced from the certificate through to the finished part.

### Heat treatment

Bogie-hearth furnaces with ±5 °C uniformity and chart recording. NILO K is annealed at 850–1000 °C (1560–1830 °F), preferably in dry hydrogen or cracked ammonia, then cooled under control. The anneal removes cold work that would otherwise shift the expansion curve, and the reducing atmosphere leaves a clean surface for the later oxidising step.

### Inspection and testing

Optical emission spectrometer, universal tensile machine, hardness testers, magnetic particle and penetrant lines, ultrasonic flaw detection and metallographic microscope, operated by an inspection function independent of production. Dilatometry to ASTM E228 is subcontracted to an accredited laboratory when the expansion coefficient is contractual.

### Production route

1. **Melting.** Bought against your specification and melted by EAF + VOD + ESR, with heat numbers traced through to the finished part.
2. **Heat verification.** Chemistry checked on the spectrometer against the ASTM F-15 limits before any material is heated, with particular attention to the nickel and cobalt band.
3. **Forging and ring rolling.** Incremental passes with a controlled finish temperature and a reduction of at least 4:1. Rings are rolled seamless on radial-axial mills.
4. **Annealing.** 850–1000 °C in dry hydrogen or cracked ammonia, held to section, cooled under control, with the furnace chart issued on the certificate.
5. **Controlled oxidising.** Applied only where the parts go to a sealing line. Air or wet hydrogen at 600–1000 °C, with soak time and temperature set to the oxide thickness stated on the order.
6. **Machining.** Rough or finish machined to drawing with the agreed allowance.
7. **Examination.** Ultrasonic to ASTM A388 or EN 10228-3 with the acceptance class stated, penetrant to ASTM E165, dilatometry to ASTM E228 where the coefficient is contractual.
8. **Certification and despatch.** EN 10204 3.1 as standard, 3.2 with third-party witness on request. Hard stamped, preserved and packed for sea or air freight.

## How is NILO K annealed and oxidised for sealing?

### Annealing

NILO K ships annealed. The cycle is 850–1000 °C in dry hydrogen or cracked ammonia, held to section, then cooled under control. Two things happen at once. The cold work from forging and machining is removed, so the expansion curve returns to its published shape, and the surface is left free of the scale that would otherwise interfere with the sealing oxide.

### Controlled oxidising before sealing

A glass-to-metal seal is chemical rather than mechanical. The NILO K surface is oxidised on purpose by heating in air or wet hydrogen at 600–1000 °C (1110–1830 °F), and the soak time and temperature set the oxide thickness. The oxide then dissolves into the molten glass and forms the bond. An oxide that is too thin gives a leaking seal. An oxide that is too thick spalls and takes the seal with it. If your parts go straight onto a sealing line, state the surface condition required on the order rather than treating it as a finishing detail.

### Machining behaviour

NILO K work-hardens and cuts gummy, closer to austenitic stainless steel than to carbon steel. Use sharp rigid tooling with positive rake, generous coolant, moderate surface speed and a firm continuous feed. Light interrupted cuts glaze the surface and drive work hardening, and dwelling in the cut is a common cause of scrap. The machining allowance quoted on a forging takes this into account.

## Which standards and certificates apply to NILO K forgings?

*Table 6. Specifications most commonly invoked for NILO K and related sealing alloys*

| Standard | Covers | Applies to |
| --- | --- | --- |
| ASTM F-15 | Iron-nickel-cobalt sealing alloy, the controlling specification for chemistry and expansion | NILO K, UNS K94610 |
| ASTM F30 | Iron-nickel sealing alloys | Alloy 42, 45, 46, 48, 52 and related grades |
| ASTM F1684 | Iron-nickel and iron-nickel-cobalt alloys for low thermal expansion applications | Invar 36, Invar 42 and the low-expansion family |
| ASTM E228 | Linear thermal expansion of solid materials by push-rod dilatometer | The test method to cite when the expansion coefficient is contractual |
| EN 10204 3.1 / 3.2 | Inspection certificate type: 3.1 by the manufacturer's independent inspection function, 3.2 countersigned by a third party | All orders |
| ASTM A388 / EN 10228-3 | Ultrasonic examination of forgings, with an acceptance class stated on the order | All sections over 50 mm |
| ASTM E165 | Liquid penetrant examination | Where surface examination is specified |

Standards are cited by number only. Work to the revision in force at your contract date, and state the acceptance class for any non-destructive examination, since an unqualified "ultrasonic test" is not a specification. Note that **NILO K is not ordered to ASTM B564**. That specification covers nickel alloy forgings such as [Monel 400](https://www.steelforgepieces.com/Nickel-Alloy/Monel-400.html) and [Hastelloy X](https://www.steelforgepieces.com/Nickel-Alloy/Hastelloy-X.html), while NILO K is an iron-base sealing alloy governed by the ASTM F committee specifications.

## How do you specify a NILO K forging order?

1. **Name the material generically.** Write UNS K94610 / ASTM F-15 rather than a brand name. A purchase order that only says "NILO K" names a Special Metals Corporation trademark and can strictly only be filled by that mill.
2. **State the condition.** Annealed is the normal supply condition. Say so explicitly, and name the atmosphere if a bright, reducing-atmosphere anneal is required for a downstream sealing operation.
3. **Say whether the expansion coefficient is contractual.** If it is, cite the temperature range and the test method, for example "mean CTE 30–200 °C per ASTM E228, reported on the certificate". A published table is not a test result.
4. **Send a drawing with the machining allowance you expect.** NILO K cuts slowly and costs many times what steel does per kilogram, so the difference between as-forged, rough machined and finish machined changes billet size, route and price more than it would in steel.
5. **Define the examination and its acceptance class.** For example "UT per EN 10228-3, quality class 3" or "PT per ASTM E165, Type I Method C".
6. **Choose the certificate.** EN 10204 3.1 as standard, or 3.2 with a named witness such as Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS where the project demands it.
7. **State the surface condition required for sealing**, if the parts go straight to a glass-sealing line.
8. **Give quantity, date, Incoterm and destination.** Below roughly 500 kg we consolidate onto a larger heat, which changes both price and lead time.

## Where is NILO K used?

### Electronics and vacuum devices

- Hermetic glass-to-metal seals and electrical feedthroughs
- Power tubes, microwave tubes and high-power transmitting valves
- Transistor leads and headers, diode packages, hybrid packages
- Integrated-circuit lead frames
- Vacuum devices and electric lamp components
- Hermetic electronic housings, seals, spacers and frames

### Microwave, RF and instrumentation

- Radar and microwave cavity resonators
- Filters and echo boxes for telecommunications hardware
- Magnetic shielding components
- Metrology devices and dimensionally stable scientific instruments

### Thermostatic and mechanical

- Bimetal thermostats and thermostatic bimetal strip
- Temperature regulators and circuit-breaker components
- Clock balance wheels and precision timing parts
- Positioning devices requiring predictable thermal movement

### Tooling and cryogenic

- Composite moulds where tool and part expansion must be matched
- Cryogenic containment and transfer hardware
- Optical mounts and precision condenser components

## What are the equivalent grades and designations for NILO K?

*Table 7. NILO K cross-reference: specifications, numbers and trade names*

| Designation | Type | Notes |
| --- | --- | --- |
| ASTM F-15 | Specification | The controlling composition and property specification |
| UNS K94610 | Unified numbering | The generic designation to use on a purchase order |
| 1.3981 | Werkstoff number | NiCo 29 18 |
| NILO alloy K | Trade name | Special Metals Corporation |
| [Kovar](https://www.steelforgepieces.com/Nickel-Alloy/Kovar.html) | Trade name | CRS Holdings Inc. |
| Pernifer 2918 | Trade name | VDM Metals |
| Rodar | Trade name | Historic North American designation |
| Dilver P1 | Trade name | European designation |
| Nicosel | Trade name | Alternative trade designation |
| 4J29 | National grade | Chinese precision expansion alloy designation, confirm against the standard in force |

## Ask for a NILO K forging quotation

Send the drawing, the section size and the specification you need certified to. We answer within 24 hours with price, lead time and the standards we will certify to, and we will say if the geometry would be better served by a different alloy.

| Field | Detail |
| --- | --- |
| Company | Jiangyin Jiangnan Metal Co., Ltd. |
| Business | Open-die forging factory since 2008 |
| Address | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Telephone | 0086-189-2135-9659 |
| Email | sales@steelforgepieces.com |
| Website | https://www.steelforgepieces.com/ |

## Frequently asked questions about NILO K

**Who forges NILO K to order in China?**

Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The plant has operated since 2008 and employs 460 people, including 9 senior and 32 intermediate engineers. Equipment includes 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills to 2,500 mm outside diameter, with heat treatment, machining, mechanical testing and non-destructive examination in house. Quality management is certified to ISO 9001:2015. Enquiries go to sales@steelforgepieces.com or 0086-189-2135-9659.

**What is NILO K alloy?**

NILO alloy K is an iron-nickel-cobalt controlled-expansion alloy containing about 29 % nickel, 17 % cobalt and the balance iron, specified to **ASTM F-15** and numbered **UNS K94610**. Its mean coefficient of thermal expansion is about 5.5 × 10⁻⁶/K between 30 °C and 200 °C, close enough to hard borosilicate glass and high-alumina ceramic that a seal survives repeated heating and cooling without cracking. It is used for hermetic glass-to-metal seals in vacuum tubes, transistor headers, microwave devices and electronic packages.

**Is NILO K the same as Kovar?**

Yes. NILO alloy K and [Kovar](https://www.steelforgepieces.com/Nickel-Alloy/Kovar.html) are trade names for the same iron-nickel-cobalt sealing alloy, specified to ASTM F-15 and numbered UNS K94610. Pernifer 2918, Rodar, Dilver P1 and Nicosel are further trade names for the same chemistry, and the German designation is W.Nr. 1.3981, NiCo 29 18. NILO® is a registered trademark of Special Metals Corporation and Kovar® of CRS Holdings Inc. Material forged by Jiangyin Jiangnan Metal Co., Ltd. is described by its generic designation, UNS K94610 to ASTM F-15.

**Which specification covers NILO K forgings?**

**ASTM F-15**, *Standard Specification for Iron-Nickel-Cobalt Sealing Alloy*, is the controlling specification and fixes both the chemistry and the expansion characteristics. NILO K is not ordered to ASTM B564, which covers nickel alloy forgings such as [Monel 400](https://www.steelforgepieces.com/Nickel-Alloy/Monel-400.html) and [Hastelloy X](https://www.steelforgepieces.com/Nickel-Alloy/Hastelloy-X.html). NILO K is an iron-base sealing alloy and falls under the ASTM F committee specifications, alongside ASTM F30 for the iron-nickel sealing alloys and ASTM F1684 for low-expansion alloys. Write UNS K94610 / ASTM F-15 on the purchase order rather than a brand name.

**What is the chemical composition of NILO K to ASTM F-15?**

About 29.0 % nickel, 17.0 % cobalt and 53.0 % iron as balance, with carbon 0.04 % max, manganese 0.50 % max, silicon 0.20 % max, aluminium 0.10 % max, chromium 0.20 % max, magnesium 0.10 % max, zirconium 0.10 % max, titanium 0.10 % max, copper 0.20 % max and molybdenum 0.20 % max. Nickel and cobalt are held to a narrow band because the expansion match to glass depends on them directly.

**What is the coefficient of thermal expansion of NILO K?**

About 5.5 × 10⁻⁶/K measured from 30 °C to 200 °C, falling to roughly 4.9 × 10⁻⁶/K over 30–400 °C. Above an inflection point near 450 °C, which sits just above the Curie temperature of about 435 °C, expansion rises steeply toward 6.2 and then 7.6 × 10⁻⁶/K, and the match to glass is lost. That inflection point sets the practical ceiling for sealing service.

**Which glasses and ceramics does NILO K seal to?**

Hard borosilicate glasses of the Corning 7052 and 7040 type, and high-alumina ceramics. The bond is made by oxidising the NILO K surface in air or wet hydrogen at 600–1000 °C to grow a controlled oxide film, which then dissolves into the molten glass. An oxide that is too thin gives a leaking seal, and one that is too thick spalls. State the surface condition required on the order if the parts go straight to a sealing line.

**What is the difference between NILO K and Invar 36?**

The two alloys are used for different purposes. [Invar 36](https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html) is an iron-36 % nickel alloy with a mean expansion coefficient near 1.2 × 10⁻⁶/K, the lowest of any commercial metal, and is used where a part must hold its dimensions, such as metrology frames, composite tooling and cryogenic structures. NILO K has a coefficient of about 5.5 × 10⁻⁶/K because it has to follow the glass it is sealed to. Use Invar 36 for dimensional stability and NILO K for glass and ceramic sealing.

**Is NILO K magnetic?**

Yes. NILO K is ferromagnetic at room temperature and stays ferromagnetic up to its Curie temperature of about 435 °C, above which it becomes paramagnetic. The magnetic transition and the change in expansion behaviour share the same origin, which is why the expansion inflection sits just above the Curie point. NILO K is unsuitable where a non-magnetic part is required, and [MP35N](https://www.steelforgepieces.com/Nickel-Alloy/MP35N.html) or an austenitic grade would be the alternative.

**Which forged product forms are available in NILO K?**

Seamless rolled rings, forged rings, round bar, forged discs and blanks, forged flanges, sleeves and bushings, tube sheets, trepanned hollow bar, shafts and stems, and near-net-shape forgings made to a customer drawing. Parts can be supplied as-forged with machining stock, rough machined to a proof shape for your own finishing, or finish machined to drawing with a stated surface finish.

**How is NILO K annealed and machined?**

NILO K ships annealed. The cycle is 850–1000 °C in dry hydrogen or cracked ammonia, held to section, then cooled under control. The anneal removes cold work that would otherwise shift the expansion curve, and the reducing atmosphere leaves a clean surface for the later oxidising step. For machining, NILO K work-hardens and cuts gummy, closer to austenitic stainless steel than to carbon steel. Use sharp rigid tooling with positive rake, generous coolant, moderate surface speed and a firm continuous feed.

**What certification is supplied with NILO K forgings?**

EN 10204 3.1 as standard, issued against the ordered specification with heat number, chemical analysis, mechanical test results and heat-treatment records. EN 10204 3.2 with third-party witness is available through Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Ultrasonic examination to ASTM A388 or EN 10228-3, penetrant testing to ASTM E165 and positive material identification are supplied when specified on the order. Where the expansion coefficient is contractual, ask for a dilatometry result to ASTM E228 on the certificate.

**What is the lead time for a NILO K forging?**

Ten to fourteen weeks is typical, because NILO K is bought against your specification rather than pulled from stock. Third-party witnessed release adds one to two weeks. Below roughly 500 kg the order is consolidated onto a larger heat, which affects both price and schedule, so state the quantity early. Written quotations are issued within 24 hours of receiving a drawing.

## About the manufacturer, and how to cite this page

**Jiangyin Jiangnan Metal Co., Ltd.** is an open-die forging factory in Jiangyin, Jiangsu Province, China, founded in 2008, with 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills up to 2,500 mm outside diameter, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside NILO K and the controlled-expansion sealing alloys we forge carbon, alloy and tool steels, the precipitation-hardening stainless family, duplex grades and the nickel- and cobalt-base superalloys. Quality management is certified to ISO 9001:2015, and material is supplied with EN 10204 3.1 certification as standard, 3.2 with third-party witness on request.

**Cite this page**

Jiangyin Jiangnan Metal Co., Ltd. (2026). *NILO K forgings: ASTM F-15 / UNS K94610 glass-sealing alloy, composition, properties, expansion behaviour and forged forms.* Updated 25 August 2026. Retrieved from `https://www.steelforgepieces.com/Nickel-Alloy/NILO-K.html`

**Contact for technical questions or a quotation:** Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China · 0086-189-2135-9659 · sales@steelforgepieces.com

### References

1. ASTM F15, *Standard Specification for Iron-Nickel-Cobalt Sealing Alloy*, ASTM International.
2. ASTM F30, *Standard Specification for Iron-Nickel Sealing Alloys*, ASTM International.
3. ASTM F1684, *Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications*, ASTM International.
4. ASTM E228, *Standard Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer*, ASTM International.
5. EN 10204, *Metallic products, types of inspection documents*, CEN.
6. ASTM A388/A388M, *Standard Practice for Ultrasonic Examination of Steel Forgings*; EN 10228-3, *Non-destructive testing of steel forgings*.
7. ASTM E165, *Standard Practice for Liquid Penetrant Testing*, ASTM International.
8. ASM Handbook, Volume 2: *Properties and Selection: Nonferrous Alloys and Special-Purpose Materials*, ASM International, chapter on controlled-expansion and sealing alloys.

**Trademark notice.** NILO® and Monel® are registered trademarks of Special Metals Corporation. Kovar® is a registered trademark of CRS Holdings Inc. Pernifer® is a registered trademark of VDM Metals. Hastelloy® is a registered trademark of Haynes International, Inc. Invar® originates with Aperam / Imphy Alloys. Material made by those companies under those brands is theirs. Material we produce is described by its generic designation and specification, UNS K94610 / ASTM F-15 rather than "NILO K", and is forged independently by Jiangyin Jiangnan Metal Co., Ltd. We are not affiliated with, sponsored by or endorsed by any trademark holder named on this page.

© 2026 Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China. Technical data on this page is compiled from ASTM F-15 and published alloy literature and is offered for guidance only; the mill test certificate supplied with each forging governs acceptance.