4J42 Alloy 42 (Fe-Ni Glass-Sealing & Lead-Frame Alloy)

4J42 (also designated 4J342) is a Chinese Fe-42Ni controlled-expansion sealing alloy, corresponding to international Alloy 42 / Nilo 42 / ASTM F30. Its coefficient of thermal expansion matches hard glass, soft glass and ceramics over a wide range, enabling reliable glass-to-metal seals. With no costly cobalt addition, it offers a cost-effective alternative to Kovar for semiconductor lead frames, electronic leads and sealed components.

Overview

• Material: 4J42 (4J342) — Fe-42Ni controlled-expansion sealing alloy
• International equivalents: Alloy 42 / Nilo 42 / ASTM F30 / UNS N14042
• Available forms: Bar, tube, plate, strip and wire

Chemical Composition (wt%)

Physical Properties

Average coefficient of thermal expansion

Mechanical Properties

Key Features

• Matching expansion: CTE matches hard glass, soft glass and ceramics for reliable hermetic seals — important in microelectronics packaging;
• Good strength in the annealed condition, maintaining shape under mechanical stress;
• Stable performance in high-temperature and corrosive environments (aerospace, chemical, energy);
• Good electrical conductivity for lead / lead-frame applications;
• Good workability, platability and weldability into complex shapes;
• Cobalt-free — lower cost than Kovar-type alloys.

Fabrication & Heat Treatment

• Forming: easy to cold and hot work into bar, tube, plate, strip and wire. Avoid excessive hot-working temperature / time and heating in sulfur-bearing atmospheres. Final cold reduction is typically around 60 % (above 75 % causes plastic anisotropy; 10–15 % reduction followed by 950–1050 °C causes excessive grain growth and can impair hermeticity of thin sections).
• Welding: readily brazed and spot-welded. Pre-oxidation is required before sealing to soft glass.
• Stress-relief annealing: 430–540 °C, hold 1–2 h, furnace or air cool.
• Intermediate annealing: in vacuum or protective atmosphere, 700–800 °C for 30–60 min, then furnace cool, air cool or water quench.
• Pre-oxidation (sealing): 1100 °C in wet hydrogen for 30 min, then oxidise in air at about 800 °C for 5–10 min; target weight gain 0.1–0.3 mg/cm².
• Note: the alloy cannot be hardened by heat treatment.
• Machining: similar to austenitic stainless steel; HSS or carbide tools, low cutting speed, coolant as required; good grindability.

Typical Applications

• Electro-vacuum: seals to soft glass and ceramics; leads, frames and sealed plugs for electron tubes, transistors and integrated circuits;
• Electronics: semiconductor lead frames;
• Temperature control: bimetal thermostat strips and bars;
• Aerospace: precision sensors and sealed components.

For detailed datasheets, mill certificates or inquiries on specific sizes and tolerances, please contact our sales & engineering team.