4J29 Kovar (Fe-Ni-Co Glass-to-Metal Sealing Alloy)

4J29 (also designated 4J329) is a Chinese Fe-Ni-Co glass-sealing alloy, the well-known Kovar (ASTM F15 / UNS K94610 / W.Nr. 1.3981). Its coefficient of thermal expansion closely matches that of hard borosilicate glass over 20–450 °C, enabling reliable hermetic glass-to-metal seals. With a high Curie point, stable low-temperature microstructure and an oxide film readily wetted by glass, it is the standard material for leads, pins, headers and envelopes in electro-vacuum and semiconductor devices.

Overview

• Material: 4J29 (4J329) — Kovar-type Fe-Ni-Co sealing alloy
• International equivalents: Kovar / ASTM F15 / UNS K94610 / W.Nr. 1.3981 / Niloy K
• Available forms: Wire, strip, sheet, plate, tube and bar

Chemical Composition (wt%)

Note: when the average coefficient of thermal expansion meets the specification, Ni and Co contents may vary within tolerance. Al, Mg, Zr and Ti are each ≤ 0.10 % and in total ≤ 0.20 %.

Physical Properties

Average coefficient of thermal expansion

Mechanical Properties

Key Features

• Matched seal: CTE closely matches hard borosilicate glass over 20–450 °C, ensuring reliable hermetic metal-to-glass seals;
• High Curie point with stable microstructure at low temperature and minimal dimensional change;
• Dense, stable oxide film readily wetted by glass, giving strong seals;
• No reaction with mercury — suitable for mercury-discharge instruments;
• Good stamping and welding performance for forming a wide range of components.

Fabrication & Heat Treatment

• Melting: Vacuum induction melting (VIM) for uniform composition and low impurities.
• Forming: rolled, forged and drawn into wire, strip, sheet, tube and bar.
• Heat treatment (in hydrogen atmosphere): heat to 900 ±20 °C and hold 1 h, then to 1100 ±20 °C and hold 15 min, followed by cooling at no more than 5 °C/min to below 200 °C before removal.
• Cold rolling: strip thickness ≥ 1.0 mm: hot-break rolling, heat treatment, pickling, conditioning, cold rolling, bright annealing, brushing, finish cold rolling, edge trimming / slitting. Strip thickness ≤ 1.0 mm (soft): cold-rolled coil slitting, bright annealing, brushing, 12-high cold rolling, bright annealing, slitting.

Typical Applications

• Electro-vacuum components: transmitting tubes, oscillator tubes, ignitrons, magnetrons, transistors, sealed plugs, relays, IC leads / pins, headers, shells and supports for reliable glass seals;
• Semiconductor devices & ICs: protective coating on external leads to prevent corrosion and ensure solderability;
• General metal-to-glass sealing components across the electronics and electro-vacuum industries.

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