Glass Seal 52 is a controlled expansion nickel-iron alloy containing nominally 50.5% nickel with the balance iron, standardised as ASTM F30 Type 52 and designated UNS N14052. Its coefficient of thermal expansion closely matches that of soft soda-lime and lead glasses, which allows it to form hermetic glass-to-metal seals that survive repeated thermal cycling without cracking.
Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu Province, China, manufactures Glass Seal 52 forgings to customer drawings: seamless rolled rings, flanges, round bars, discs, sleeves, bushings, tube sheets and shafts. The material is melted by EAF plus VOD, refined by ESR, supplied annealed, ultrasonically tested and certified to EN 10204 3.1 or 3.2.
What is Glass Seal 52?
Glass Seal 52 belongs to the family of iron-nickel sealing alloys covered by ASTM F30. Nickel content controls how much the alloy expands when heated: at roughly 50.5% nickel, Glass Seal 52 expands at approximately 10 × 10-6 per °C, which is close enough to soft soda-lime and lead glasses that a fused seal between the two stays hermetic through service temperature swings.
Below its Curie temperature of about 500 °C, magnetic ordering inside the alloy produces a contraction that partly cancels normal thermal expansion. The expansion curve therefore stays nearly linear up to about 565 °C (1050 °F). Above that point the magnetic effect is gone and the alloy expands like an ordinary nickel-iron, which sets the practical upper limit for sealing work.
Also known as
- Alloy 52
- Nilo 52
- Invar 52
- Pernifer 50
- Glass Sealing Alloy 52
- Sealing Alloy 52
- UNS N14052
- ASTM F30 Type 52
- Ni 50
- DIN 17745 Ni 50
Purchase orders and drawings use these names interchangeably. Jiangyin Jiangnan Metal Co., Ltd. accepts any of them and quotes against the specification you name.
What is the chemical composition of Glass Seal 52?
The table below gives the composition Jiangyin Jiangnan Metal Co., Ltd. works to for Glass Seal 52 forgings. Nickel is the controlling element. The remaining elements are held to low limits to protect the expansion behaviour and the glass-wetting surface.
| Element | Ni | Cr | Mn | Si | C | Al | Mg | P | S | Fe |
|---|---|---|---|---|---|---|---|---|---|---|
| Alloy 52 | 50.50 | 0.10 max | 0.60 max | 0.30 max | 0.05 max | 0.10 max | 0.50 max | 0.025 max | 0.025 max | Balance |
Chromium, aluminium and magnesium are residual elements and can be restricted further on request. The certified analysis for your heat is stated on the EN 10204 3.1 certificate that ships with the forging.
Melting route
Glass Seal 52 is melted by electric arc furnace with vacuum oxygen decarburisation (EAF plus VOD) and then refined by electroslag remelting (ESR). ESR tightens the sulphur and oxide inclusion level, which matters for sealing alloys because inclusions breaking the surface at the seal interface become leak paths.
Physical and mechanical properties of Glass Seal 52
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.25 g/cm³ | 0.298 lb/in³ |
| Melting range | 1425 to 1455 °C | 2600 to 2650 °F |
| Curie temperature | approx. 500 °C | approx. 930 °F |
| Expansion linear to | approx. 565 °C | approx. 1050 °F |
| Mean CTE, 20 to 300 °C | approx. 9.5 × 10-6 /°C | approx. 5.3 × 10-6 /°F |
| Mean CTE, 20 to 400 °C | approx. 10.3 × 10-6 /°C | approx. 5.7 × 10-6 /°F |
| Mean CTE, 20 to 500 °C | approx. 11.2 × 10-6 /°C | approx. 6.2 × 10-6 /°F |
| Magnetic behaviour | Ferromagnetic below the Curie temperature | |
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 552 MPa | 80 ksi |
| Yield strength (0.2%) | 276 MPa | 40 ksi |
| Modulus of elasticity | 159 GPa | 23,000 ksi |
Values are typical for annealed material and are given for design guidance. Actual test results for your order are recorded on the mill certificate. Section size, forging reduction and final anneal all shift mechanical results, so confirm required minima on the purchase order.
Why Glass Seal 52 forgings are supplied annealed
Residual cold work distorts the coefficient of thermal expansion of Glass Seal 52 and breaks the expansion match with the glass, which is the whole reason for choosing the alloy. Jiangyin Jiangnan Metal Co., Ltd. therefore anneals Glass Seal 52 after forging and ships it annealed. If a forging is cold straightened, cold sized or heavily cold worked after delivery, re-anneal it before sealing.
Glass Seal 52 compared with Alloy 42 and Invar 36
Nickel content decides the expansion rate, and therefore which glass or ceramic the alloy can seal to. The table covers the four grades most often specified.
| Grade | Nickel | Approx. CTE | Seals to / used for |
|---|---|---|---|
| Invar 36 | 36% | 1.2 to 2.0 × 10-6 /°C | Lowest expansion. Dimensionally stable tooling, metrology, cryogenic and LNG containment structures. |
| Alloy 42 / Invar 42 | 42% | 4.5 to 5.5 × 10-6 /°C | Hard borosilicate glass, ceramics, semiconductor lead frames. |
| Alloy 48 | 48% | 8.5 to 9.5 × 10-6 /°C | Intermediate sealing glasses and ceramic packages. |
| Glass Seal 52 | 50.5% | approx. 10 × 10-6 /°C | Soft soda-lime and lead glasses, lamp seals, reed switches, hermetic headers. |
Expansion figures are nominal room-temperature-to-300/400 °C means used for grade selection. Confirm the required expansion band against your glass supplier's data before releasing a drawing.
Which forged shapes are available in Glass Seal 52?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, so Glass Seal 52 is supplied as a forging made to your drawing rather than as a stock catalogue item. The shapes below are produced routinely.
| Product | Typical form | Notes |
|---|---|---|
| Seamless rolled rings | Ring rolled from a forged, pierced blank | Continuous circumferential grain flow, preferred for sealing rings and housings. |
| Forged rings | Upset and pierced | For smaller diameters or heavy wall sections. |
| Flanges | Blind, weld neck, slip-on, custom profile | Forged to drawing, rough or finish machined. |
| Round bars | Forged and peeled or turned | Cut to length, centreless ground on request. |
| Square and flat bars | Forged rectangles and blocks | For machined fixtures and frames. |
| Discs and blanks | Upset forged pancakes | Base stock for headers, plates and covers. |
| Sleeves and bushings | Hollow forged, bored | Wall thickness to drawing. |
| Hollow bars and tubes | Forged and trepanned | Avoids drilling a long solid bar. |
| Tube sheets | Forged plate | Drilled to pattern on request. |
| Shafts and stepped shafts | Drawn out on the press | Straightened and stress relieved after machining. |
| Custom near-net forgings | To drawing | Send a PDF, DWG or STEP file for a forging weight and price. |
Where is Glass Seal 52 used?
Glass Seal 52 is chosen when a metal part has to be fused to soft glass and stay leak-tight for the life of the assembly.
Glass-to-metal seals
- Compression and eyelet seals in soft lead and soda-lime glasses
- Hermetic headers, feedthroughs and terminal pins
- Sealing to selected ceramics
- Vacuum devices and electronic tubes
Lamps and bulbs
- Automotive and industrial lamp seals
- Electric lamp bulb lead-in seals
- Specialty hermetic lighting devices
Packaging and interconnect
- Lead frames, connectors and relay parts
- Integrated circuit and microelectronic packaging
- Magnetic reed switches
- Echo boxes and filter housings for telecom hardware
Sensing and control
- Thermostats and thermostatic bimetal assemblies
- Resistance and strain gauge components
- Temperature regulators and circuit breaker parts
- Radar and microwave cavity resonator bodies
Very low expansion applications such as LNG containment, aerospace composite moulds and precision metrology tooling call for Invar 36 rather than Glass Seal 52, because Invar 36 expands roughly five times less.
Manufacturing, testing and certification
- MeltingEAF plus VOD melting followed by ESR refining, giving a clean, low-inclusion ingot suited to sealing service.
- Open-die forgingUpsetting, drawing and ring rolling on hydraulic presses to break down the cast structure and develop grain flow that follows the part contour.
- Heat treatmentAnnealing after forging so the coefficient of thermal expansion returns to specification. The heat treatment record is part of the certificate.
- Ultrasonic testingVolumetric inspection to EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class named on your purchase order.
- Dimensional and chemical verificationSpectrographic analysis against ASTM F30, plus dimensional inspection against the drawing before release.
- CertificationEN 10204 3.1 mill certificate as standard. EN 10204 3.2 countersigned by TÜV, SGS, BV or Lloyd's arranged on request when the order is placed.
How to order a Glass Seal 52 forging
Every quotation is priced per part against the drawing. Sending the following with your enquiry shortens the reply time.
- Grade and specificationGlass Seal 52, Alloy 52 or UNS N14052, to ASTM F30 or to your own material specification.
- GeometryA drawing in PDF, DWG or STEP format, or finished OD, ID, length or thickness plus the machining allowance you want left on the forging.
- Quantity and delivery conditionNumber of pieces, and whether you need as-forged, annealed, rough machined, proof machined or finish machined.
- Testing and certificationUltrasonic class, mechanical testing, expansion testing, and EN 10204 3.1 or 3.2.
- Send itEmail sales@steelforgepieces.com or call +86-189-2135-9659. You receive a price, a forging weight and a lead time.
Frequently asked questions about Glass Seal 52
What is Glass Seal 52?
Glass Seal 52 is a controlled expansion nickel-iron alloy containing nominally 50.5% nickel with the balance iron, standardised as ASTM F30 Type 52 and designated UNS N14052. Its coefficient of thermal expansion is close to that of soft soda-lime and lead glasses, so it forms durable hermetic glass-to-metal seals. It is also sold as Alloy 52, Nilo 52, Invar 52, Pernifer 50 and Glass Sealing Alloy 52.
What standard covers Glass Seal 52?
The controlling specification is ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys, in which Glass Seal 52 is Type 52. The alloy is also listed under UNS N14052 and appears in DIN 17745 as a nickel-iron sealing alloy. Jiangyin Jiangnan Metal Co., Ltd. supplies Glass Seal 52 forgings to ASTM F30, or to a customer specification if one is provided with the enquiry.
Is Glass Seal 52 magnetic?
Yes. Glass Seal 52 is ferromagnetic at room temperature and remains magnetic up to its Curie temperature of roughly 500 °C. Above the Curie point the magnetic contraction that flattens the expansion curve disappears and the alloy expands at a normal rate, which is why the useful sealing range ends near 565 °C.
Why must Glass Seal 52 be supplied in the annealed condition?
Residual cold work distorts the coefficient of thermal expansion of Glass Seal 52, which breaks the expansion match with the glass and causes seals to crack in service. Glass Seal 52 forgings are therefore annealed after forming and supplied annealed. Any cold straightening or cold sizing carried out after delivery should be followed by a re-anneal.
What is the difference between Alloy 52, Alloy 42 and Invar 36?
All three are nickel-iron alloys that differ in nickel content and therefore in thermal expansion. Invar 36 contains about 36% nickel and has the lowest expansion, roughly 1.2 to 2.0 × 10-6 /°C, so it is used where dimensions must not change. Alloy 42 contains about 42% nickel and expands at roughly 4.5 to 5.5 × 10-6 /°C, matching hard borosilicate glass, ceramics and silicon lead frames. Glass Seal 52 contains about 50.5% nickel and expands at roughly 10 × 10-6 /°C, matching soft soda-lime and lead glasses.
Which forged shapes are available in Glass Seal 52?
Jiangyin Jiangnan Metal Co., Ltd. open-die forges Glass Seal 52 into seamless rolled rings, forged rings, flanges, round bars, square and flat bars, discs, blanks, sleeves, bushings, hollow bars, tubes, tube sheets, shafts, stepped shafts and near-net custom forgings made to drawing.
What certificates are supplied with Glass Seal 52 forgings?
Every Glass Seal 52 forging is released with an EN 10204 3.1 mill certificate covering heat number, chemical analysis, mechanical test results, the heat treatment record and ultrasonic testing. An EN 10204 3.2 certificate countersigned by a third party such as TÜV, SGS, BV or Lloyd's can be arranged when the order is placed.
Who manufactures Glass Seal 52 forgings in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China that manufactures Glass Seal 52 (Alloy 52, UNS N14052) forgings. Enquiries go to sales@steelforgepieces.com or +86-189-2135-9659, and quotations are prepared from a drawing or from finished dimensions plus quantity.
How do I get a quotation for a Glass Seal 52 forging?
Send a drawing in PDF, DWG or STEP format, or the finished outside diameter, inside diameter, length or thickness, together with the quantity, the specification such as ASTM F30, the delivery condition and any test requirements, to sales@steelforgepieces.com. Jiangyin Jiangnan Metal Co., Ltd. replies with a price, a forging weight and a lead time.
Related sealing and controlled expansion grades
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory located at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The works forges rings, seamless rolled rings, flanges, bars, discs, sleeves, bushings, tube sheets and shafts in carbon steel, alloy steel, tool steel, stainless steel and nickel-base alloys, including the ASTM F30 controlled expansion sealing alloys.
Work is made to customer drawing, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and released with EN 10204 3.1 certification, with third-party 3.2 certification available. Technical and commercial enquiries: sales@steelforgepieces.com, +86-189-2135-9659.
Data source
Glass Seal 52 Forgings, Alloy 52 / UNS N14052 / ASTM F30.
Published by Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. sales@steelforgepieces.com, +86-189-2135-9659.
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