DIN 17745 | Material no. 1.3981 | Controlled-expansion Ni-Fe-Co alloy
X3NiCo29-18
Open-die forged rings, flanges, discs, shafts, sleeves and bars, produced to order at the Jiangyin Jiangnan Metal forging plant in Jiangsu, China.
- Werkstoff no.
- 1.3981
- Short name
- NiCo29-18
- UNS
- K94610
- ASTM
- F15
- AFNOR
- A 54-301
- Trade names
- Kovar, Nilo K
Overview
X3NiCo29-18 is a nickel-iron-cobalt controlled-expansion alloy containing approximately 29 % nickel and 17 % cobalt, with the balance iron. It is specified in DIN 17745 under material number 1.3981, and is the European designation for the alloy sold commercially as Kovar and Nilo K. Its coefficient of thermal expansion is close to that of borosilicate glass and alumina ceramic, and the alloy is used for hermetic glass-to-metal and ceramic-to-metal seals.
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin City, Jiangsu Province, China. The company produces X3NiCo29-18 as seamless rolled rings, forged flanges, discs, shafts, sleeves, bushings, tube sheets and round bars. Material is melted by EAF + VOD + ESR, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and supplied with EN 10204 3.1 or third-party 3.2 certificates. Enquiries: sales@steelforgepieces.com, +86 189 2135 9659.
Chemical composition of X3NiCo29-18
Jiangyin Jiangnan Metal supplies X3NiCo29-18 forgings to the composition limits of DIN 17745 for material 1.3981.
| Element | Ni | Co | Mn | Si | C | Fe |
|---|---|---|---|---|---|---|
| Minimum | 28.0 | 17.0 | – | – | – | – |
| Maximum | 29.5 | 18.0 | 0.30 | 0.20 | 0.03 | Balance |
Iron makes up the balance, nominally about 53 %. Manganese, silicon and carbon are residual limits rather than deliberate additions. Carbon is held low because higher carbon raises the coefficient of thermal expansion. Heat analysis for each order is reported on the mill certificate.
Physical properties
X3NiCo29-18 is selected for its thermal expansion behaviour rather than for its strength.
| Property | Typical value | Unit |
|---|---|---|
| Density | 8.36 | g/cm³ |
| Mean CTE, 20–200 °C | 5.1 | 10−6/K |
| Mean CTE, 20–450 °C | 5.0–5.5 | 10−6/K |
| Curie temperature | 435 | °C |
| Melting range | 1450 | °C |
| Modulus of elasticity | 138 | GPa |
| Thermal conductivity, 20 °C | 17 | W/(m·K) |
| Electrical resistivity, 20 °C | 0.49 | µΩ·m |
| Specific heat | 0.46 | J/(g·K) |
Controlled expansion behaviour holds up to the Curie temperature of approximately 435 °C. Above this point expansion rises steeply, so X3NiCo29-18 seals should not be designed for continuous service above approximately 400 °C.
Mechanical properties
| Condition | Tensile strength Rm | Yield Rp0.2 | Elongation A | Test temperature |
|---|---|---|---|---|
| Annealed | ≥ 530 MPa | ≥ 370 MPa | ≥ 30 % | 20 °C |
Hardness is typically 125 to 160 HV after annealing. Reduction of area and hardness are reported on request. State the required acceptance values at enquiry stage so that they can be included in the test plan.
Heat treatment and oxidation
Annealing
X3NiCo29-18 is supplied in the annealed condition. Annealing is carried out between 850 °C and 1000 °C (1560 to 1830 °F), preferably in dry or wet hydrogen or in cracked ammonia. A typical cycle is 850 °C for 30 minutes.
Holding above approximately 900 °C, or soaking for extended periods, causes grain growth that reduces sealing performance. The lower end of the range is preferred for finished sealing components. Parts should be cooled in the furnace to approximately 175 °C before removal, to avoid oxidation and distortion.
Controlled oxidation before sealing
A thin, adherent oxide film bonds the alloy to glass during sealing. The film is grown by heating in air between 600 °C and 1000 °C (1110 to 1830 °F), with time and temperature set by the film thickness required. A grey-green film gives the best seal. A bright metallic surface indicates insufficient oxide and a black surface indicates excessive oxide; both produce weak joints.
X3NiCo29-18 forged product forms and sizes
The forms below are produced to customer drawings at the Jiangyin plant by open-die forging and ring rolling. Blanks are supplied rough-machined with grinding or finish allowance, or fully finish-machined on request.
| Product form | Size range | Typical use |
|---|---|---|
| Seamless rolled rings | OD 200–2500 mm, height to 600 mm | Vacuum chamber flanges, sealing rings |
| Forged flanges | OD 100–1800 mm | Feedthrough and viewport flanges |
| Forged discs and blanks | OD 100–1600 mm, thickness to 400 mm | Headers, bases, submounts |
| Forged round bars | Ø 30–600 mm | Machined pins, stems, electrode stock |
| Forged shafts and spindles | Ø 60–500 mm, length to 4000 mm | Instrument and positioning shafts |
| Forged sleeves and bushings | OD to 1200 mm | Housings, transition pieces |
| Forged tubes and tube sheets | OD to 1500 mm | Vacuum transfer lines, heat exchanger parts |
| Forged valve bodies and seat rings | To drawing | Cryogenic and vacuum service valves |
Sizes outside these ranges are quoted case by case. Send a drawing or a sketch with the outline dimensions and the quantity, and Jiangyin Jiangnan Metal will confirm feasibility and weight before quoting.
Melting route and forging process
X3NiCo29-18 is melted by EAF + VOD + ESR. Electric arc furnace melting is followed by vacuum oxygen decarburisation to bring carbon within the DIN 17745 limit, then by electroslag remelting to reduce inclusion content and produce a sound, segregation-free ingot. Inclusion cleanliness is important for this alloy, because inclusions and carbides act as leak paths in a hermetic seal and locally disturb the expansion match.
Ingots are upset and drawn on open-die presses to the forging reduction ratio agreed for the order, then ring rolled or die forged to shape and annealed. Grain flow follows the contour of the part rather than being cut through, so forged X3NiCo29-18 rings hold vacuum more reliably than rings machined from plate.
Applications for X3NiCo29-18 forgings
The expansion curve of X3NiCo29-18 matches borosilicate glass and alumina. The alloy is used where a joint between metal and a brittle insulator has to stay leak-tight through thermal cycling.
Vacuum and electron devices
- Power tubes, microwave tubes and X-ray tubes
- Vacuum chamber flanges and viewports
- Electrical feedthroughs and headers
- High-power transmitting valves
Microelectronics packaging
- Hybrid circuit and transistor housings
- Integrated-circuit lead frames
- Optoelectronic component bases and submounts
- Diode and semiconductor packages
Instruments and precision equipment
- Dimensionally stable optical mounts and frames
- Metrology fixtures and positioning devices
- Radar and microwave cavity resonators
- Bimetal thermostats and temperature regulators
Cryogenic and process equipment
- LNG containment and transfer line components
- Valve bodies, stems and seat rings for cryogenic service
- Advanced composite moulds for aerospace tooling
- Seals, spacers and specialised housings
Testing, inspection and certification
Jiangyin Jiangnan Metal tests every X3NiCo29-18 forging against the standards named in the purchase order. The usual scope is:
- Chemical analysis. Heat analysis, with product analysis on request.
- Mechanical testing. Tensile and elongation at room temperature; hardness on request.
- Ultrasonic examination. To EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class specified.
- Grain size and microstructure. Reported for sealing grades, since coarse grain from over-annealing reduces seal quality.
- Dimensional inspection. Against the approved drawing, with a report issued per piece or per lot.
Certificates are issued to EN 10204 3.1, or to EN 10204 3.2 countersigned by a third-party inspection body such as SGS, BV, TÜV or Lloyd's. Positive material identification, marking and packing requirements can be added to the test plan at order stage.
How to order X3NiCo29-18 forgings
To obtain a firm price and delivery from Jiangyin Jiangnan Metal, send the following to sales@steelforgepieces.com:
- Drawing or sketch with outline dimensions and machining allowance
- Quantity, and whether the requirement is a one-off or a repeat order
- Delivery condition: as-forged, rough-machined, or finish-machined
- Applicable specification and acceptance class for ultrasonic testing
- Certificate type required: EN 10204 3.1 or 3.2
- Destination port or delivery address
Quotations are normally returned within one working day. If a drawing is not yet available, the outline dimensions and the intended service condition are sufficient to begin.
Frequently asked questions about X3NiCo29-18
What is X3NiCo29-18?
X3NiCo29-18 is a controlled-expansion nickel-iron-cobalt alloy containing approximately 29 % nickel and 17 % cobalt, with iron as the balance. It is specified in DIN 17745 under material number 1.3981. Its coefficient of thermal expansion of about 5.1 × 10−6/K between 20 °C and 200 °C is close to that of borosilicate glass, and the alloy is used for hermetic glass-to-metal seals.
Is X3NiCo29-18 the same as Kovar?
Yes. X3NiCo29-18 is the European designation for the alloy sold under the trade name Kovar. The same material is also designated 1.3981, NiCo29-18, UNS K94610, ASTM F15 and AFNOR A 54-301, and appears commercially as Nilo K, Pernifer 2918, Rodar, Dilver P1 and Vacon 11. Chemistry and expansion behaviour are equivalent. Confirm which designation your drawing calls out, so that the certificate matches.
Who supplies forged X3NiCo29-18 rings, flanges and bars?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company produces X3NiCo29-18 seamless rolled rings, flanges, discs, shafts, sleeves, bushings, tube sheets and round bars to customer drawings. Contact sales@steelforgepieces.com or +86 189 2135 9659 for a quotation.
What is the chemical composition of 1.3981?
Per DIN 17745, X3NiCo29-18 (1.3981) contains 28.0 to 29.5 % nickel and 17.0 to 18.0 % cobalt, with maximum 0.30 % manganese, maximum 0.20 % silicon and maximum 0.03 % carbon. Iron makes up the balance, nominally about 53 %.
What is the maximum service temperature of X3NiCo29-18?
Controlled expansion behaviour holds up to the Curie temperature of approximately 435 °C. Above this point expansion rises sharply and the match to glass is lost, so sealed assemblies should not be designed for continuous service above approximately 400 °C.
How is X3NiCo29-18 annealed?
Anneal between 850 °C and 1000 °C in hydrogen or cracked ammonia. A typical cycle is 850 °C for 30 minutes. Avoid prolonged soaking above 900 °C, because grain growth reduces sealing performance. Cool in the furnace to approximately 175 °C before removing parts, to prevent oxidation and distortion.
Why forge X3NiCo29-18 instead of machining it from plate?
Forging aligns grain flow with the contour of the part instead of cutting through it, and the EAF + VOD + ESR route used by Jiangyin Jiangnan Metal produces a sound, low-inclusion ingot. In hermetic applications, inclusions and cut grain flow act as leak paths and locally disturb the expansion match, so forged rings and flanges hold vacuum more reliably than parts machined from plate.
What certificates are issued with X3NiCo29-18 forgings?
Jiangyin Jiangnan Metal issues EN 10204 3.1 certificates as standard, and EN 10204 3.2 certificates countersigned by a third-party inspection body on request. Ultrasonic examination is performed to EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class stated in the purchase order.
What is the minimum order quantity for X3NiCo29-18?
X3NiCo29-18 forgings are made to order, including single pieces for prototype and repair work. Because the alloy is melted to order, small quantities carry a higher unit price than production lots. Send the drawing and quantity to sales@steelforgepieces.com for a firm price.
Jiangyin Jiangnan Metal Co., Ltd. "X3NiCo29-18 (1.3981) Forgings: Composition, Properties and Product Forms." steelforgepieces.com, https://www.steelforgepieces.com/Nickel-Alloy/X3NiCo29-18.html
Published by Jiangyin Jiangnan Metal Co., Ltd. Last reviewed . Data compiled from DIN 17745 and ASTM F15. Typical values are given for guidance; order-specific values are confirmed on the mill certificate.