Alloy 42

Controlled Expansion Alloy

Manufactured in accordance with ASTM F30 and designated as UNS K94100, Alloy 42 is engineered to deliver a consistently low coefficient of thermal expansion over a wide temperature range - typically from 20 °C to 300 °C, and up to 450 °C in some applications.

This predictable thermal expansion makes alloy 42 ideal for hermetic sealing applications involving glass and ceramic materials. Its expansion characteristics closely match those of silicon and advanced ceramics, such as alumina, beryllia, and vitreous glass, ensuring durable, leak-free glass-to-metal and ceramic-to-metal seals.

Thanks to its dimensional stability under thermal cycling, iron nickel 42 is widely specified in electronic, aerospace, and high-reliability industrial applications where precision and long-term performance are critical.

Heat Treatment

Alloy 42 (UNS K94100) is typically supplied in the annealed condition per ASTM F30 specifications, with unannealed bars available upon request to meet specific application needs. Machined components should be annealed in an inert gas atmosphere for 30 minutes per inch thickness at 788 °C and furnace cooled.

Machining

Alloy 42 can be work hardened, so it is essential to keep the material cool and tool speed low. Nickel iron alloys can seem to be rather soft and gummy during machining compared to regular stainless steels.