Iron-nickel sealing alloy · UNS N14052 · 4J50
Alloy 52 forgings: rings, bars, discs and flanges
A 50.5 % nickel controlled-expansion alloy for glass-to-metal seals, forged to your drawing in Jiangyin, China.
Alloy 52 is a binary iron-nickel alloy of nominally 50.5 % nickel, balance iron, whose thermal expansion is matched to soft lead and soda-lime sealing glasses. It carries the number UNS N14052, is called 4J50 in China, and its chemistry was set by ASTM F30 until that standard was withdrawn in 2024. It is used where a metal part has to stay hermetically sealed to glass or ceramic through repeated heating and cooling: reed switches, lamp and electron-tube hardware, feedthroughs and sealed housings.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, that forges Alloy 52 into seamless rolled rings, round bars, discs, flanges, shafts, sleeves, bushings and tube sheets. Material is melted by the EAF + VOD + ESR route, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and certified to EN 10204 3.1 or 3.2. Enquiries: sales@steelforgepieces.com, +86 189 2135 9659.
- Nominal nickel
- 50.5 %balance iron
- Mean CTE
- 9.8×10⁻⁶/K, 25–450 °C
- Curie point
- ~500 °Cexpansion inflection
- Tensile, min
- 552MPa (80 ksi)
What Alloy 52 is
In the iron-nickel system, between roughly 30 % and 55 % nickel, thermal expansion is set by the nickel content rather than being a fixed property of the metal. Raise the nickel and expansion rises. Lower it and expansion falls. The grades in this family are named after their nickel level for that reason.
Alloy 52 sits at the top of the sealing range, at a nominal 50.5 % nickel. Its expansion follows that of soft lead and soda-lime glass closely, so a seal between the two carries only a small residual stress after cooling from the glass annealing point to room temperature. A poor match shows up later as the glass pulling away from the metal, or as radial cracks.
ASTM F30 treated the nickel percentages as nominal and required the producer to adjust nickel in the melt until the expansion requirement was met. The certified expansion value is therefore the controlling figure, not the nickel percentage. If the seal design depends on a particular coefficient over a particular temperature range, state that figure on the purchase order.
Designations and equivalents
| Designation | System or origin | Notes |
|---|---|---|
| Alloy 52 | Common trade name | The name most drawings use. |
| UNS N14052 | UNS, used in ASTM F30 | The number to quote on a purchase order. |
| UNS K95050 | UNS | Also quoted by some suppliers for this alloy. Confirm which number your specification means. |
| 4J50 | China, GB/T | The domestic grade. Permits carbon to 0.05 %. |
| ASTM F30 | ASTM International | Iron-Nickel Sealing Alloys. Withdrawn 2024. |
| AMS-I-23011 Class 2 | SAE / former MIL-I-23011 | Noncurrent. Not recommended for new designs. |
| Nilo 50 | Special Metals Corporation | Trademarked product name. |
| Pernifer 50 | VDM Metals | Trademarked product name. |
| Glass Sealing 52, Glass Seal 52, 52 Alloy, N52 | Trade usage | Generic descriptive names. |
| Invar 52 | Loose trade usage | Invar is a trademark of ArcelorMittal and properly means the 36 % Ni alloy. Treat “Invar 52” as a search term, not a specification. |
Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as Alloy 52 / UNS N14052 / 4J50. We are not affiliated with, sponsored by or endorsed by any of the trademark holders named above.
ASTM F30 was withdrawn in 2024. What to write instead.
ASTM Committee F01 retired the glass-sealing alloy specification family, withdrawing F30 (iron-nickel sealing alloys) together with F15, F29 and F31. There is no direct ASTM replacement. The alloys have not changed. Three routes are in common use:
- Name the last issue explicitly, as in chemistry and expansion to ASTM F30-96(2017), withdrawn, agreed as reference. Certificates can then cite a fixed document.
- Buy to GB/T grade 4J50, which remains current.
- Buy to a company specification that states the chemistry limits and the required mean coefficient of expansion with its temperature range.
Jiangyin Jiangnan Metal certifies Alloy 52 forgings against whichever of these the order names. Ordering to a withdrawn standard without saying so is the most common cause of a certificate being rejected at goods-in.
Chemical composition
| Grade | 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 | Rem |
Nickel is a nominal figure. It is adjusted within the melt so that the thermal expansion requirement is met, and cobalt, when present as an incidental element, is reported separately on the certificate.
Mechanical properties
| Property | Imperial | Metric |
|---|---|---|
| Tensile strength | 80 ksi min | 552 MPa min |
| Yield strength | 40 ksi min | 276 MPa min |
| Elongation | 35 % min | 35 % min |
Physical and thermal properties
| Property | Typical value |
|---|---|
| Density | 8.3 g/cm³ (0.30 lb/in³) |
| Melting range | approx. 1,425–1,450 °C |
| Curie temperature | approx. 500 °C |
| Expansion linear to | approx. 565 °C (1,050 °F) |
| Electrical resistivity at 20 °C | approx. 43 µΩ·cm |
| Thermal conductivity, 20–100 °C | approx. 14 W/m·K |
| Magnetic | Ferromagnetic below the Curie point |
| Temperature range | Mean CTE, ×10⁻⁶/K | µin/in·°F |
|---|---|---|
| 20–300 °C | 9.8 – 10.5 | 5.4 – 5.8 |
| 25–450 °C | 9.8 | 5.4 |
| 20–500 °C | 9.2 – 10.0 | 5.1 – 5.6 |
Published typical values, for comparison and first-pass design. The coefficient certified for your heat is the figure that governs the seal. State the range you need on the enquiry and we will measure and report it.
Where Alloy 52 sits in the sealing family
Nickel content sets expansion, and expansion is the reason to choose one of these grades over another. The scale below places the five common iron-nickel grades against the expansion band of soft lead and soda-lime sealing glass. Alloy 52 falls inside that band and Alloy 48 falls just below it.
| Grade | Nominal Ni | Typical CTE ×10⁻⁶/K | Normally matched to | UNS |
|---|---|---|---|---|
| Invar 36 | 36 % | ~1.5 | Nothing. Chosen for dimensional stability, moulds, metrology, LNG. | K93600 |
| Alloy 42 | 41 % | ~4.3–5.8 | Hard borosilicate glass, alumina, silicon. Lead frames. | K94100 |
| Alloy 46 | 46 % | ~7.5 | Intermediate soft glasses. | K94600 |
| Alloy 48 | 48 % | ~8.7 | Soft lead and soda-lime glass. Industrial thermostats. | K94800 |
| Alloy 52 | 50.5 % | ~9.8–10.5 | Soft lead and soda-lime glass, some ceramics. Reed switches, lamps, electron tubes. | N14052 |
Select on the expansion of the glass or ceramic being sealed to. If the drawing gives a coefficient and a temperature range but no grade, send us the coefficient and we will propose the grade.
Forged product forms
All forms below are made from Alloy 52 to drawing. Ring rolling is the usual route for annular parts. It gives circumferential grain flow, which suits sealing rings and flange rings better than a part cut from plate or bar.
Seamless rolled rings
Sealing rings, flange rings, housing rings and gear ring blanks, rolled on 3 m and 6 m mills.
Forged flanges
Blind, weld-neck, slip-on and custom profile flanges, as forged or machined.
Forged round bars
Bar stock for turned feedthroughs, pins, eyelets and machined sealing bodies.
Forged discs and blanks
Disc and disk blanks for covers, headers and seal plates.
Forged shafts and spindles
Shafts, eccentric shafts, spindles and stepped shafts.
Forged sleeves and bushings
Sleeves, bushings and cylindrical housings.
Forged tube sheets and pipes
Tube sheets, forged pipe and tube, hollow bar.
Valve components
Valve bodies, seat rings, stems and blocks for ball, check, globe, gate and plug valves.
Works capability and size envelope
| Item | Capability |
|---|---|
| Open-die hammers | 1 t, 3 t, 5 t and 9 t |
| Hydraulic press | 5,000 t |
| Ring-rolling mills | 3 m and 6 m |
| Diameter range | 80 mm to 6,000 mm |
| Length | up to 12,000 mm |
| Single-piece weight | 10 kg to 15,000 kg |
| Workforce | approx. 460, including 9 senior and 32 intermediate engineers |
That envelope covers the whole works. Alloy 52 parts are normally ordered well inside it, since sealing components are usually small. Send us the finished dimensions and we will confirm the forging route and the ingot size.
Melting, forging and heat treatment
- Melting. EAF melting with VOD refining, followed by electroslag remelting. ESR reduces sulphur and oxide inclusions and evens out composition through the ingot. Expansion follows nickel closely, so compositional uniformity is what holds the coefficient steady across a forging cross-section.
- Forging. Ingot is upset and drawn under the hammers or the press, then punched and rolled if the part is a ring. Forging reduction breaks up the as-cast structure and gives a wrought grain flow.
- Heat treatment. Annealing is the normal condition. Normalising, hardening and tempering are available where a drawing calls for them. If your sealing process depends on grain size or on the surface condition entering pre-oxidation, state the anneal temperature and atmosphere on the order.
- Machining. Supplied as forged, rough machined with a stated allowance, or finish machined to drawing.
- Inspection. Dimensional check, chemistry, mechanical test and ultrasonic examination before release.
Testing and certification
| Test | Standard or equipment |
|---|---|
| Ultrasonic examination | EN 10228-3, SEP 1921 or ASTM A388, to the quality class named on the order |
| Magnetic particle | Magnetic particle flaw detection equipment on site |
| Tensile and yield | Universal testing machine |
| Impact | Impact testing machine |
| Hardness | Hardness testing machine |
| Microstructure | Metallographic microscope |
| Chemistry | Reported per heat on the certificate |
| Certificate | EN 10204 3.1, or 3.2 witnessed by a third party such as SGS, BV, TUV or Lloyd's |
Applications of Alloy 52 forgings
Glass-to-metal and ceramic-to-metal seals
Seals for electron tubes, automotive and industrial lamps, and hermetic devices. Sealing rings, flange rings, forged shafts and forged pipe are used where the joint has to stay vacuum-tight through thermal cycling. Alloy 52 is the grade intended for lead sealing glasses.
Reed switches and electronic hardware
Reed switch blades and housings, echo boxes and filters for mobile telephones, small transformer parts, and magnetic shielding. Alloy 52 is ferromagnetic below its Curie point and has fairly high saturation induction and permeability, which is why it is used for reed switch parts.
Microwave, radar and precision instruments
Cavity resonators for radar and microwave equipment, precision condenser blades, specialised electronic housings, and dimensionally stable instrument and optical mountings.
Thermostatic and control components
One component of thermostatic bimetal strip, bimetal thermostats, temperature regulators and electrical circuit-breaker parts.
Valve and process components
Forged valve stems, seat rings, blocks and bodies for ball, check, globe, gate and plug valves and strainers, where a controlled-expansion body is specified.
Tooling and cryogenic hardware
Composite moulds for aerospace, positioning devices, and containers and transfer lines for LNG service, where low or matched expansion is the reason for the material choice.
How to specify Alloy 52 on a purchase order
- Grade and designation. Write Alloy 52 with UNS N14052 or 4J50. Because ASTM F30 is withdrawn, add the wording to the chemistry and expansion limits of ASTM F30-96(2017) so the certificate can cite a fixed document.
- Required expansion. Give the mean coefficient and the temperature range over which it is measured. This is what actually controls the heat.
- Dimensions. Send a drawing, or the finished OD, ID, height or length, and say whether you want the part as forged, rough machined or finish machined.
- Heat treatment. Annealed unless stated. Give temperature and atmosphere if your sealing process depends on them.
- Testing. Name the ultrasonic standard and quality class, and any additional tests.
- Certificate. EN 10204 3.1, or 3.2 with the inspection body you want to witness it.
- Quantity and delivery. Piece count, whether this is a prototype or a repeat order, and the date you need it.
Send the enquiry to sales@steelforgepieces.com or call +86 189 2135 9659.
Terms used on this page
| Term | Meaning |
|---|---|
| Controlled-expansion alloy | An alloy chosen because its coefficient of thermal expansion is a specified value, rather than for strength or corrosion resistance. |
| Mean CTE | The average coefficient of linear thermal expansion between two stated temperatures. It is meaningless without the temperature range. |
| Curie temperature | The temperature at which the alloy loses ferromagnetism and its expansion rises steeply. Seal designs stay below it. |
| Annealing point (glass) | The temperature at which glass stops flowing and starts behaving elastically. Seal stress builds between this point and room temperature. |
| Hermetic seal | A joint whose leak rate is below a defined limit, normally verified by helium leak test. |
| ESR | Electroslag remelting. A refining remelt that improves cleanliness and reduces segregation. |
| VOD | Vacuum oxygen decarburisation. A ladle refining step that lowers carbon and gas content. |
| EN 10204 3.1 / 3.2 | Inspection certificate issued by the maker's independent inspection function (3.1), or witnessed by an independent third party (3.2). |
| Seamless rolled ring | A ring made by piercing a forged preform and rolling it out, giving continuous circumferential grain flow. |
Frequently asked questions about Alloy 52
What is Alloy 52?
Alloy 52 is a binary iron-nickel controlled-expansion alloy containing a nominal 50.5 % nickel with the balance iron. It is designated UNS N14052, known in China as 4J50, and its chemistry was covered by ASTM F30 until that standard was withdrawn in 2024. Its coefficient of thermal expansion is matched to soft lead and soda-lime sealing glasses, so a glass-to-metal seal made with it stays hermetic through temperature cycling. Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China, supplies it as seamless rolled rings, forged bars, discs, flanges, shafts, sleeves and tube sheets.
What is the chemical composition of Alloy 52?
Nickel 50.50 %, chromium 0.10 % max, manganese 0.60 % max, silicon 0.30 % max, carbon 0.05 % max, aluminium 0.10 % max, magnesium 0.50 % max, phosphorus 0.025 % max, sulphur 0.025 % max, iron remainder. The nickel figure is nominal: it is adjusted within the melt so the thermal expansion requirement is met, so the certified expansion value governs rather than the nickel percentage alone.
Is Alloy 52 the same as Nilo 50, Pernifer 50, Invar 52 or UNS N14052?
They refer to the same 50.5 % nickel alloy. Nilo is a trademark of Special Metals Corporation and Pernifer of VDM Metals, so Nilo 50 and Pernifer 50 name those companies' branded versions. Glass Sealing 52, Glass Seal 52, 52 Alloy and N52 are generic trade names. UNS N14052 is the number used in ASTM F30; some suppliers quote UNS K95050 for the same alloy, so confirm which your specification means. Invar 52 is loose usage: Invar is a trademark of ArcelorMittal and properly refers to the 36 % nickel alloy.
Which standard covers Alloy 52 now that ASTM F30 is withdrawn?
ASTM withdrew F30 in 2024, along with F15, F29 and F31, when Committee F01 retired the glass-sealing alloy specification family. There is no direct ASTM replacement. Buyers normally continue to purchase to the chemistry and expansion limits of the last issue, ASTM F30-96(2017), naming it on the order as a withdrawn but agreed reference; or buy to the Chinese grade 4J50; or buy to a company specification. Jiangyin Jiangnan Metal certifies against whichever the order names.
What is the thermal expansion coefficient of Alloy 52?
Typical published mean coefficients are about 9.8 ×10⁻⁶/K over 25 to 450 °C, roughly 9.8 to 10.5 over 20 to 300 °C, and roughly 9.2 to 10.0 over 20 to 500 °C. Expansion is close to linear up to about 565 °C. These are indicative; the value certified for your heat is what governs the seal design.
What is the difference between Alloy 52, Alloy 48, Alloy 46, Alloy 42 and Invar 36?
Same iron-nickel system at different nickel levels, and nickel sets the expansion. Invar 36 has the lowest expansion, about 1.5 ×10⁻⁶/K, and is used for dimensional stability rather than sealing. Alloy 42 at about 41 % nickel seals to hard borosilicate glass, alumina and silicon. Alloy 46 and Alloy 48 sit between. Alloy 52 at 50.5 % has the highest expansion of the group and is matched to soft lead and soda-lime glasses and to reed switch and lamp hardware.
Can Alloy 52 be made as a seamless rolled ring?
Yes. Jiangyin Jiangnan Metal rolls Alloy 52 seamless rings on 3 m and 6 m ring-rolling mills, with the preform upset and punched under 1, 3, 5 and 9 tonne open-die hammers or a 5,000 tonne hydraulic press. Ring rolling gives a circumferential grain flow that suits sealing rings, flange rings and housing rings better than a part cut from plate or bar.
What testing and certification comes with the forgings?
Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388 as named on the order. The works holds a universal testing machine, impact tester, hardness tester, metallographic microscope and magnetic particle equipment. Certificates are issued to EN 10204 3.1, or 3.2 witnessed by a third party such as SGS, BV, TUV or Lloyd's.
Who supplies Alloy 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, producing Alloy 52 (UNS N14052 / 4J50) forgings to drawing. The works employs about 460 people including 9 senior and 32 intermediate engineers, and runs 1, 3, 5 and 9 tonne open-die hammers, a 5,000 tonne hydraulic press and 3 m and 6 m ring-rolling mills. Contact sales@steelforgepieces.com or +86 189 2135 9659.
What sizes and weights of Alloy 52 forgings can be produced?
The works envelope is 80 mm to 6,000 mm diameter, up to 12,000 mm length, and 10 kg to 15,000 kg single-piece weight. Alloy 52 parts are normally ordered well inside that envelope. Send the finished dimensions and the forging route and ingot size will be confirmed.
Nilo® is a registered trademark of Special Metals Corporation. Pernifer® is a registered trademark of VDM Metals. Invar® is a registered trademark of ArcelorMittal. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is described as Alloy 52 / UNS N14052 / 4J50, the generic chemistry, manufactured independently. We are not affiliated with, sponsored by or endorsed by any of the trademark holders named.