4J36 Invar 36 (Fe-Ni Low Expansion Alloy)

4J36 (also designated 4J336) is a Chinese Fe-36Ni low-expansion alloy, the well-known Invar 36 (UNS K93600 / W.Nr. 1.3912). It has an ultra-low coefficient of thermal expansion from about −250 °C to 200 °C, combined with good ductility, toughness and low-temperature mechanical properties, making it the standard material where dimensional stability against temperature change is critical.

Overview

• Material: 4J36 (4J336) — Invar 36 (Fe-36Ni) low-expansion alloy
• International equivalents: Invar 36 / Nilo 36 / UNS K93600 / W.Nr. 1.3912 / ASTM F1684
• Available forms: Bar, plate, strip, sheet, wire, tube and forgings

Chemical Composition (wt%)

Physical Properties

Average coefficient of thermal expansion

Mechanical Properties

Key Features

• Ultra-low expansion: dimensions barely change with temperature from −250 °C to 200 °C, meeting demanding precision requirements;
• Good ductility and toughness, easy to form and resistant to brittle fracture;
• Good strength and toughness retained at cryogenic temperatures;
• Good corrosion resistance in room-temperature dry air.

Fabrication & Heat Treatment

• Melting: Vacuum induction melting (VIM) for uniform composition and low impurities.
• Forming: rolled, forged and drawn into bar, plate, strip, wire and tube.
• Stress-relief annealing: 530–550 °C, hold 1–2 h, furnace cool.
• Intermediate annealing: 830–880 °C, hold 30 min, furnace cool or air cool.
• Stabilising treatment: quench from 830 °C (hold 20 min–1 h in protective atmosphere); then heat to 315 °C for 1–4 h and furnace cool; finally hold at 95 °C for 48 h. For precision parts after cold or machining: stress-relief stabilising at 315–370 °C for 1–4 h.
• Surface preparation: sand blasting, polishing or pickling; oxide scale can be removed in 25 % HCl solution at 70 °C.
• Machining: similar to austenitic stainless steel; HSS or carbide tools, low cutting speed, coolant as required; good grindability.

Typical Applications

• Liquefied-gas production, storage and transport equipment — the low expansion prevents leaks caused by temperature change;
• Measurement and control instruments operating below 200 °C, ensuring accuracy and stability across temperatures;
• Temperature-regulating devices;
• Threaded connection bushings between metal and other materials, preventing loosening from differential thermal expansion;
• Components of bimetal and thermal bimetal temperature-control elements;
• Tempering dies for CRP (continuous-reinforced / composite) components in aviation;
• Satellite and missile electronic-control-unit frames below −200 °C, maintaining dimensional stability in cryogenic service;
• Auxiliary electron tubes in electromagnetic lenses of laser-control devices.

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