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Alloy 42 (4J42) Iron-Nickel Controlled-Expansion Sealing Alloy
1. Product Overview
Alloy 42 (Chinese designation 4J42, UNS K94100, German standard 1.3917) is an iron-nickel controlled-expansion sealing alloy containing about 41.5%–42.5% nickel. By precisely locking the nickel content within the binary iron-nickel system, the alloy gives a mean coefficient of linear thermal expansion that closely approaches that of soft glass and 95% alumina ceramics over the sealing temperature range, so that a low-stress, highly hermetic seal interface forms after cooling. Typical values are a mean coefficient of linear thermal expansion of 4.0–5.0×10⁻⁶/°C at 20–300 °C, and at 20–450 °C it is 6.5–6.7×10⁻⁶/°C.
A controlled-expansion sealing alloy is a special class of functional material: its value lies not in strength or corrosion resistance but in the requirement that its dimensional change with temperature stay in step with that of the glass or ceramic. Once the expansion behavior of the metal and of the sealing material diverges, enormous thermal stress builds up at the interface during cooling, which at best cracks the glass and at worst debonds the seal interface and destroys hermeticity. 4J42 is precisely the binary iron-nickel alloy designed to solve this problem.
Overview at a Glance
Item | Details | ||
Material category | Iron-nickel controlled-expansion sealing alloy (Fe-Ni42, Ni 41.5%–42.5%) | ||
Key properties | Expansion match with soft glass and 95% alumina ceramics · cobalt-free, low cost · excellent deep-drawing and etching behavior | ||
Available forms | Cold-rolled strip · plate · bar · wire · flat wire · capillary tube · sealing rings and shaped blanks | ||
Typical industries | Integrated-circuit lead frames · vacuum electron devices · semiconductor packaging · lighting · optical communication · precision instruments | ||
Applicable standards | GB/T 15018 / YB/T 5235 / ASTM F30 / AMS 5683 / DIN 17745 | ||
Mean CTE (20–300 °C) | Density | Tensile strength, annealed condition | Curie temperature |
4.0–5.0×10⁻⁶/°C | 8.10–8.12 g/cm³ | 450–550 MPa | ≈360 °C |
2. Chemical Composition (GB / YB Systems)
Table 3-4 Chemical composition of 4J42 (GB/T 15018 and YB/T 5235 systems, wt%)
Element | Content / max. | Element | Content / max. |
Ni | 41.5–42.5 | Fe | Balance |
C | ≤0.05 | Mn | ≤0.80 (≤0.50 in some standards) |
Si | ≤0.30 | P | ≤0.020 |
S | ≤0.020 | Co | ≤1.0 |
Cr | ≤0.20 | Al | ≤0.10 |
Ti | ≤0.10 | Cu, Mo and other residuals | Controlled per standard |
In this system, the width of the nickel range directly determines both cost and how well the properties can be controlled: the narrower the range, the better the lot-to-lot consistency of expansion behavior, but the harder and more costly the melting control. Manganese and silicon are present as conventional deoxidizing elements that also improve hot workability, but excessive levels raise the expansion coefficient markedly, so their upper limits are set very low. Phosphorus and sulfur, in turn, affect hot ductility and the cleanliness of the seal interface.
3. Chemical Composition (ASTM / International Systems)
Chemical composition of Alloy 42 (ASTM F30 and other international systems, wt%)
Element | Content / max. | Element | Content / max. |
Ni | 41.0–42.5 | Fe | Balance |
C | ≤0.05 | Mn | ≤0.50–0.80 |
Si | ≤0.30 | P | ≤0.020 |
S | ≤0.020 | Co | ≤0.50–1.0 |
Cr | ≤0.20 | Al | ≤0.10 |
Ti | ≤0.10 | Cu | ≤0.20 |
The comparison shows that the international systems set a slightly wider nickel lower limit (from 41.0%), and that the stated limits for manganese, cobalt and other elements vary with the standard revision.
4. Designations, Standards and Equivalents
(1) Designation cross-reference
Main designation equivalents for Alloy 42 / 4J42
Country / system | Equivalent designation | Notes |
China | 4J42 (also written as Fe-Ni42) | Standard designation in the Chinese national system; the most widely used |
United States | Alloy 42 / UNS K94100 / Glass Sealing 42 | UNS number used for material identification and database searches |
United States (trade name) | Nilo 42 | Common international vendor trade name |
Germany | 1.3917 / Vacogil 42 / NSD N42 | W.Nr numbering widely used on European drawings |
Russia | 42H | Equivalent designation in the Russian system |
Japan | YEF42 | Designation widely used by Japanese manufacturers |
United Kingdom | Uniseal 42 | British trade name for sealing alloys |
(2) List of main applicable standards
Applicable standards commonly used for Alloy 42 / 4J42
Standard | Scope | Application notes |
GB/T 15018 | Classification and designations of precision alloys | Basic Chinese standard for designation naming and system classification |
GB/T 15015 | Technical requirements for controlled-expansion sealing alloys | Covers dimensional tolerances, properties and inspection rules |
YB/T 5235 | Iron-nickel sealing alloys for vacuum electron devices | Core delivery basis for the electron tube and vacuum electronics industry |
ASTM F30 | Iron-nickel sealing alloys (including Alloy 42) | General US material standard, often cited in international purchasing |
AMS 5683 | Alloy 42 bar, wire and forgings for aerospace | Aerospace applications with stricter testing and certification requirements |
DIN 17745 | Chemical composition of iron-nickel alloys | Composition basis in the German/European system |
ISO 9723 | Specification for nickel-iron alloy bar | Corresponding ISO specification |
5. Key Performance Parameters
(1) Expansion properties
Alloy 42 (4J42): Mean coefficient of linear thermal expansion (hydrogen-annealed condition, reference values)
Temperature range | Mean CTE (×10⁻⁶/°C) | Engineering notes |
20–100 °C | 5.6 | Slightly higher at room temperature, affected by the low-temperature martensitic transformation |
20–200 °C | 4.9 | Enters the stable low-expansion range |
20–300 °C | 4.0–5.0 (typical 4.8) | Main temperature range specified by the standard |
20–400 °C | 5.9 | Near the Curie point, the curve begins to rise |
20–450 °C | 6.5–6.7 (typical 6.9) | Key temperature range for ceramic sealing processes |
20–500 °C | 7.8 | Close to the upper limit of soft-glass sealing temperature |
20–600 °C | 9.2 | Beyond the usual sealing range; for reference only |
(2) Physical properties
Typical physical properties of Alloy 42 / 4J42 (reference values)
Property | Typical value | Property | Typical value |
Density | 8.10–8.12 g/cm³ | Electrical resistivity | 0.45–0.61 µΩ·m |
Curie temperature | ≈360 °C (380 °C in some sources) | Magnetic state | Ferromagnetic below the Curie temperature |
Elastic modulus (annealed) | ≈155 GPa | Elastic modulus (cold-worked) | ≈160 GPa |
Crystal structure | Face-centered cubic austenitic structure | Melting range | About 1420–1450 °C |
Nickel content | 41.5%–42.5% (41.0%–42.5% in some systems) | Cobalt content | ≤1.0% (usually not added) |
Thermal conductivity | About 10–11 W/(m·K) in magnitude | Appearance | Silvery-white metallic luster |
The Curie temperature is often overlooked, yet it has direct engineering significance: 4J42 is ferromagnetic below about 360 °C, and this magnetism, which stems from the ordered iron-nickel structure, is also the physical basis of the low expansion; once the Curie temperature is exceeded, the magnetism disappears and the expansion behavior changes markedly. Therefore, whenever the sealing process temperature has to go beyond 400 °C, the matching of the expansion curves must be rechecked rather than simply extrapolated from room-temperature data.
(3) Mechanical properties
Alloy 42/4J42 mechanical properties (typical values and standard requirements)
Property | Annealed condition | 50% cold-worked | Notes |
Tensile strength Rm | 450–550 MPa (≥490) | 850–950 MPa | Marked work hardening; strength nearly doubles |
Yield strength Rp0.2 | 180–250 MPa | 700–800 MPa | Yield-to-tensile ratio rises sharply with cold work |
Elongation | ≥30%–35% | ≥5% | Deep drawing and bending must be carried out in the annealed condition |
Hardness HV | 130–170 | — | Moderate hardness in the annealed condition, which favors die life |
Hardness HRB | 60–80 | 90–100 | HRB can be used to judge the supplied condition quickly |
Elastic modulus | ≈155 GPa | ≈160 GPa | Used for terminal normal force and springback calculations |
6. Available Forms and Size Ranges
Strip is the main form in which 4J42 is traded, followed by bar and wire. The form determines not only the subsequent processing route but also the technical details of how expansion properties are sampled and guaranteed. The size ranges and availability are described below in two groups.
(1) Strip, plate and foil
Common supply sizes for Alloy 42/4J42 strip and plate (the actual available range is subject to confirmation at the time of order)
Form | Thickness range | Width range | Common delivery condition |
Ultra-thin cold-rolled strip | 0.05–0.20 mm | 5–300 mm | Hard and soft (low yield, price premium) |
Standard cold-rolled strip | 0.20–1.50 mm | 5–300 mm | Soft, half-hard, hard |
Thicker cold-rolled strip | 1.50–3.50 mm | By agreement | Hot-rolled or cold-rolled + annealed |
Medium-thick plate | 3.0–40 mm | By agreement; cut to length available | Hot-rolled + annealed and pickled or ground |
Slit strip | As per incoming thickness | Slit to customer-specified width | Delivered deburred |
Two factors that are easily underestimated when buying strip are thickness tolerance and flatness. In a lead frame stamped continuously on a high-speed progressive die, thickness variation directly causes pitch errors and burrs, so such applications usually require a tighter thickness tolerance band (on the order of ±0.005 mm) and strict control of camber and wavy edges. Ultra-thin strip below 0.2 mm, however, involves many rolling passes, more annealing cycles and a low yield, so the unit price is noticeably higher; this is normal rather than an inflated quotation.
(2) Bar, wire, tube and custom parts
Supply ranges for Alloy 42/4J42 bar, wire, tube and custom parts
Form | Common size range | Delivery condition | Typical applications |
Bar | Φ5–180 mm | Hot-rolled, peeled, ground, annealed | Machined sealing rings, support posts, bases |
Wire | Φ0.10–6.0 mm | Cold-drawn, bright-annealed, cut to length | Lead-out wires, lamp leads, woven mesh |
Flat wire | Cross-section customized to drawing | Cold-rolled, annealed | Lead terminals with special cross-sections |
Capillary tube | OD 1.0–8.0 mm, wall thickness by agreement | Cold-drawn, annealed, cut to length | Sensors, medical and vacuum electron device components |
Sealing rings | Per drawing | Machined + hydrogen annealed | Electron tubes, traveling-wave tubes, magnetrons |
Shaped forging blanks | Per drawing | Forged + annealed | Structural parts for optical communication and precision instruments |
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