Hangbo Alloy Group
Shanghai · Est. 2012
UNS K94100 / W.Nr. 1.3917 — Iron-nickel controlled-expansion alloy with CTE matched to borosilicate glass and alumina ceramic for hermetic seals in electronic packaging.
Alloy 42 (UNS K94100 / W.Nr. 1.3917, also known as Nilo 42, Invar 42, and Fe-Ni 42) is a binary nickel-iron alloy containing approximately 42% nickel with the balance iron. It belongs to the family of controlled-expansion iron-nickel alloys and is engineered specifically to provide a coefficient of thermal expansion (CTE) that closely matches borosilicate glass and certain alumina ceramics over the temperature range encountered during device fabrication and operation.
The defining feature of Alloy 42 is its thermal expansion curve. The mean coefficient from 20 to 300 °C is approximately 4.5–5.5 × 10−6/°C, which is close to the expansion of Corning 7050/7052/7056 borosilicate glasses (about 4.6 × 10−6/°C) and standard 95% alumina ceramic (about 6.5 × 10−6/°C). This match allows the formation of strong, hermetic glass-to-metal seals that survive thermal cycling, solder reflow, and long-term operation without cracking or stress-induced leakage.
Alloy 42 has a face-centered cubic (FCC) austenitic structure in the annealed condition. It is essentially non-magnetic at room temperature with relative permeability near 1.0, which is critical for reed switches, magnetic sensors, and certain electronic devices. Cold working raises permeability through strain-induced ordering, so light final anneals are used to restore non-magnetic behavior when needed. The Curie temperature of approximately 380 °C marks the upper end of useful non-magnetic service.
Commercially, Alloy 42 is most often supplied as precision cold-rolled strip in thicknesses from 0.05 mm to 3.0 mm, slit to customer widths for lead frame stamping. Wire, round bar, plate, and ribbon are also produced. Strip and wire are typically supplied with controlled surface finishes and optional electrodeposited or thermally grown oxide for improved glass wetting during sealing.
At Hangbo Alloy Group, Alloy 42 is melted by vacuum induction melting (VIM) followed by electroslag remelting (ESR) or vacuum arc remelting (VAR) where required, then hot-worked, cold-rolled to final gauge with precision anneals, and slit to width. Each lot is fully tested for chemical composition, expansion behavior (using a high-precision dilatometer to verify the CTE curve against ASTM F30 limits), tensile strength, hardness, surface finish, and grain size.
The chemical composition of Alloy 42 is tightly specified because small deviations in nickel content or residual element level can significantly shift the coefficient of thermal expansion. The composition window of 40–43% Ni is the sweet spot where the expansion curve matches common sealing glasses; dropping below 40% Ni raises the expansion toward pure iron (~12 × 10−6/°C), while raising it above 50% Ni pulls the expansion down toward Invar-grade low values. Manganese, silicon, and chromium residuals are kept low to avoid disrupting the Fe-Ni phase behavior.
For semiconductor-grade strip, the residual levels of sulfur, phosphorus, and non-metallic inclusions are further restricted to ensure clean stamping and reliable plating. Hangbo Alloy Group can provide material with extra-low residuals per customer specification for the most demanding IC and sensor applications.
| Element | Min % | Max % |
|---|---|---|
| Iron (Fe) | Balance | Balance |
| Nickel (Ni) | 40.0 | 43.0 |
| Manganese (Mn) | — | 0.80 |
| Silicon (Si) | — | 0.30 |
| Carbon (C) | — | 0.05 |
| Chromium (Cr) | — | 0.25 |
| Aluminum (Al) | — | 0.10 |
| Cobalt (Co) | — | 0.50 |
| Copper (Cu) | — | 0.20 |
| Phosphorus (P) | — | 0.025 |
| Sulfur (S) | — | 0.025 |
| Chromium + Molybdenum (Cr+Mo) | — | 0.50 |
Alloy 42 has a stable FCC austenitic structure in the annealed condition. Its physical properties—moderate density, low electrical resistivity, and low thermal conductivity—are characteristic of Fe-Ni binary alloys. The thermal expansion curve is the most important physical parameter; it is verified on every heat using a calibrated dilatometer from room temperature to 500 °C, and the slope is checked against the customer-specified glass sealing window.
Because the alloy is non-magnetic in the fully annealed state, it is favored for reed switches, MRI components, and electronic devices that must not perturb magnetic fields. The Curie temperature of approximately 380 °C defines the upper limit of non-magnetic behavior; above this point the alloy becomes ferromagnetic. For most glass-sealing and packaging applications the operating temperature stays well below this limit.
| Property | Value | Unit |
|---|---|---|
| Density | 8.12 | g/cm³ |
| Melting Point | ~1440 | °C |
| Specific Heat (20–100 °C) | 515 | J/kg·K |
| Thermal Conductivity (20 °C) | 14.7 | W/m·K |
| Electrical Resistivity (20 °C) | 0.66 | μΩ·m |
| Modulus of Elasticity (20 °C) | 148 | GPa |
| Curie Temperature | ~380 | °C |
| Mean CTE (20–100 °C) | 4.0–4.5 | × 10−6/°C |
| Mean CTE (20–300 °C) | 4.5–5.5 | × 10−6/°C |
| Mean CTE (20–450 °C) | 6.5–7.5 | × 10−6/°C |
| Relative Permeability (annealed) | ~1.0 | — |
The mechanical properties of Alloy 42 are strongly dependent on cold work. In the fully annealed condition the alloy is soft and ductile, with tensile strength of 490–585 MPa, yield strength of 270–345 MPa, and elongation of 30–43%. Cold rolling to higher tempers progressively increases strength and reduces elongation, which is useful for spring contacts and high-strength lead frames. Strip for semiconductor lead frames is commonly supplied in the 1/2-hard to full-hard temper range.
Hardness in the annealed state is typically 70–85 HRB; cold-rolled strip can reach 90 HRB and above. The alloy has excellent formability in the annealed condition, allowing deep drawing of headers and cups, and is readily stamped, blanked, and coined. Welded, brazed, and soldered joints can be produced using standard Ni-Fe filler metals; however, glass-sealing temperatures are typically above 700 °C in air, so atmosphere control (wet hydrogen, vacuum, or inert gas) is essential to prevent excessive oxidation.
| Property | Annealed | 1/2 Hard | Full Hard |
|---|---|---|---|
| Tensile Strength | 490–585 MPa (71–85 ksi) | 620–760 MPa (90–110 ksi) | 830–1030 MPa (120–150 ksi) |
| Yield Strength (0.2%) | 270–345 MPa (39–50 ksi) | 480–620 MPa (70–90 ksi) | 700–900 MPa (102–130 ksi) |
| Elongation (in 50 mm) | 30–43% | 8–20% | 2–6% |
| Hardness (typical) | 70–85 HRB | 85–95 HRB | 25–30 HRC |
The thermal expansion behavior of Alloy 42 is its defining engineering characteristic. When matched to a specific sealing glass, the alloy and glass expand at nearly the same rate through the entire thermal cycle from sealing temperature down to room temperature, minimizing residual stress. This is essential because a thermally mismatched seal will develop tensile or compressive stresses at the interface, leading to micro-cracking, helium leak failures, and shortened device life.
Common matched glass systems include:
For best sealing results, the surface of the Alloy 42 is pre-oxidized in a controlled wet-hydrogen atmosphere at 600–900 °C to form a thin, uniform iron-rich oxide layer about 2–5 μm thick. This oxide dissolves into the molten glass during sealing, producing a strong chemical bond. The pre-oxidation step is critical: too little oxide gives a weak seal, too much causes poor wetting and pinholes. Hangbo Alloy Group supplies strip with pre-oxidized finish (typically per ASTM F30 or customer specification) and works closely with customers to dial in oxide thickness for their specific glass system.
Alloy 42 is not a corrosion-resistant alloy; it contains no significant chromium and behaves essentially like a low-carbon steel in most environments. It is intended primarily for use in dry, sealed atmospheres or for short-term exposure during device fabrication. For electronic packaging, the alloy is enclosed within a glass or ceramic seal, so atmospheric corrosion is rarely a concern. Outside of sealed environments, Alloy 42 can be protected by nickel, gold, tin, or solder plating.
Alloy 42 is readily fabricated using standard metalworking processes. Cold working increases strength rapidly, so intermediate anneals are used during severe forming. Annealing is performed in dry hydrogen, vacuum, or inert atmosphere at 800–900 °C to avoid excessive surface oxidation. After the final anneal, the surface can be conditioned (pickled, bright-etched, or pre-oxidized) depending on the application.
Alloy 42 is one of the most widely used controlled-expansion alloys in the world, with applications concentrated in electronic, semiconductor, and hermetic-seal industries. Its unique combination of matched CTE, non-magnetic behavior, and excellent formability has made it the standard material for a wide range of devices.
Hangbo Alloy Group manufactures and supplies Alloy 42 in a comprehensive range of product forms and sizes, all supported by material test reports and third-party inspection. Our typical supply scope includes:
| Standard | Description |
|---|---|
| ASTM F30 | Iron-Nickel Controlled-Expansion Alloys (Plate, Sheet, Strip) |
| ASTM F1684 | Iron-Nickel Low-Expansion Alloy Plate, Sheet, and Strip |
| ASTM B753 | Iron-Nickel Controlled-Expansion Alloy Strip |
| DIN 17745 | Wrought Iron-Nickel Alloys with Controlled Expansion (W.Nr. 1.3917) |
| GB/T 4339 | Chinese Standard for Iron-Nickel Controlled Expansion Alloys |
| JIS H2501 | Japanese Standard for Controlled Expansion Alloys |
| IEC 60404-8-4 | Cold-Rolled Electrical Alloy Strip |
| QQ-N-290 | Nickel-Iron Alloy (older US federal specification) |
Alloy 42 (UNS K94100) is a binary iron-nickel alloy containing about 42% nickel. Its defining feature is a coefficient of thermal expansion closely matched to borosilicate glass and certain ceramics, allowing hermetic glass-to-metal and ceramic-to-metal seals. It is also non-magnetic in the annealed condition and highly formable.
Alloy 42 contains 40–43% nickel with the balance iron. Residuals are strictly limited: C ≤ 0.05%, Mn ≤ 0.80%, Si ≤ 0.30%, Cr ≤ 0.25%, Al ≤ 0.10%, P ≤ 0.025%, S ≤ 0.025%. The narrow composition window is essential for stable, predictable CTE behavior.
The mean CTE of Alloy 42 is 4.5–5.5 × 10−6/°C between 20 and 300 °C. This is very close to the expansion of Corning 7050/7052/7056 borosilicate glass (~4.6 × 10−6/°C) and 95% alumina ceramic above 200 °C, making Alloy 42 the standard material for matched glass-sealing applications.
Alloy 42 is covered by ASTM F30 (controlled expansion alloy strip and sheet), ASTM F1684, ASTM B753, DIN 17745 (W.Nr. 1.3917), GB/T 4339, JIS H2501, and IEC 60404-8-4. Strip for electronic applications is also supplied per customer-specific semiconductor standards.
In the annealed condition, tensile strength is 490–585 MPa (71–85 ksi) and yield strength is 270–345 MPa (39–50 ksi), with elongation of 30–43%. Cold-rolled strip can reach tensile strengths above 900 MPa. Strip for lead frame stamping is commonly supplied in 1/2-hard to full-hard tempers.
Alloy 42 is essentially non-magnetic at room temperature in the fully annealed condition (relative permeability near 1.0). Cold working increases permeability through strain-induced ordering. At temperatures above its Curie point (~380 °C), the alloy becomes ferromagnetic.
Invar 36 (Fe-36Ni) has lower CTE near room temperature (~1.2 × 10−6/°C) and is used for cryogenic and precision instruments. Alloy 42 (Fe-42Ni) has higher CTE (~4.5–5.5 × 10−6/°C) that is much closer to borosilicate glass and alumina, making it the better choice for hermetic seals. Alloy 42 is also higher in strength and more weldable.
Alloy 42 is designed for use from cryogenic temperatures up to about 350–400 °C for controlled expansion behavior. Glass-sealing transition temperature is 600–650 °C. Above approximately 400 °C the CTE curve begins to shift and the alloy becomes magnetic past its Curie point (~380 °C).
Primary applications include glass-to-metal seals in TO headers, IC packages, reed switches, diode envelopes, and vacuum tubes; semiconductor lead frames; ceramic-to-metal seals in power electronics; thermostat bimetals; reed switches and magnetic sensors; and lamp lead-in wires for halogen, HID, and fluorescent lighting.
Hangbo Alloy Group supplies cold-rolled strip (0.05–3.0 mm, slit to width), wire (0.10–8.0 mm), round bar (6–300 mm), plate, foil down to 0.025 mm, pre-oxidized strip for direct glass sealing, and plated strip and wire (nickel, gold, tin, silver, or solder finishes) per customer specification.
Alloy 42 pricing is sensitive to nickel market price. Cold-rolled strip in standard thicknesses (0.1–1.0 mm) typically ranges USD 25–45 per kilogram FOB Shanghai in 2026 market conditions. Stamping-grade precision strip and tighter flatness tolerances command premium pricing. Wire and bar forms are usually 15–25% lower per kilogram than thin strip.
Standard sizes of cold-rolled Alloy 42 strip ship from stock in 3–7 days. Custom slit widths or thicknesses require 2–4 weeks. Minimum order quantity is typically 5–10 kg for stock strip and 50–100 kg for custom slitting. Mill quantities (≥ 500 kg) lead time is 4–6 weeks.
Hangbo Alloy Group maintains mill-direct supply of Alloy 42 strip, wire, bar, plate, and pre-oxidized strip in both standard and custom configurations. Our team can assist with CTE matching to your specific glass system, surface finish specification, temper selection, and export documentation. We support customers in semiconductor packaging, electronic component manufacturing, lighting, and aerospace electronics industries with reliable quality and fast delivery.
For quotations, material certifications, or technical consultation, contact our sales team or call +86-136-1165-6360. We typically respond within 10 minutes.
Request a quotation for Alloy 42 strip, wire, bar, or plate. We stock standard sizes and accept custom slitting, plating, and pre-oxidation orders.