Description
4J24 Kovar alloy is an iron-nickel-cobalt-based precision alloy with fixed thermal expansion. Its core characteristic lies in possessing a linear expansion coefficient (approximately 4.6–5.2 × 10⁻⁶/°C) comparable to that of hard glass within the temperature range of 20–450°C, enabling high-hermeticity sealing. The standard designation for this alloy is 4J24, classified within the controlled thermal expansion alloy family. It finds primary application in electro-vacuum components, precision instrumentation, and semiconductor packaging. For deep cryogenic applications, additional requirements for microstructural stability at -196°C have been introduced to prevent volume expansion failures caused by austenite-to-martensite phase transformation.
Grades
|
International standards |
||||
|
ASTM |
GB |
EN |
DIN |
JIS |
|
UNS K94610 |
GB/T 15018-1994 |
Nilo K |
1.3981 |
KV-1 |
|
4J42 |
||||
Chemical composition
Chemical composition % by mass MAX unless otherwise stated
|
Element |
Min% |
Max% |
|
C |
- |
0.03 |
|
Si |
- |
0.30 |
|
Mn |
- |
0.50 |
|
P |
- |
0.02 |
|
S |
- |
0.02 |
|
Co |
16.8 |
17.8 |
|
Ni |
28.5 |
29.5 |
|
Fe |
Bal |
Bal |
Alloy Details
1.Thermal Expansion Compatibility
Within the 20–450°C range, its linear expansion coefficient is (4.6–5.2) × 10⁻⁶/°C, exhibiting high compatibility with borosilicate hard glass (e.g., Pyrex) and 95% alumina ceramics. This ensures stress-free bonding interfaces without cracking.
2.Mechanical and Physical Properties
Strength and Ductility:
- Tensile strength ≥530 MPa in annealed state, elongation ≥30%.
- Cold-rolled strength reaches 800 MPa, though ductility reduces to ≥5%.
Density and Melting Point:
- Density 8.17 g/cm³, melting point approximately 1450°C.
- Electrical and Thermal Conductivity: Resistivity 46 μΩ·cm, thermal conductivity 21.4–26.8 W/(m·K) (100–400°C).
3.Structural Stability
Curie point 430°C; maintains low expansion characteristics below this temperature. Trace elements (e.g., P, S ≤ 0.020%) require strict control to prevent volume expansion failure due to phase transitions.
|
Processing stage |
Competitive advantage |
Application case |
|
Cold-rolled forming |
Surface free from orange peel defects when single-pass reduction rate ≤15%, thin sheet (0.1–2mm) thickness tolerance ±0.01mm |
Optical communication TO package cover plate |
|
Sealing Pre-treatment |
800°C pre-oxidation forms Fe-Co-Ni composite oxide film with glass interface bond strength >120MPa |
X-ray tube glass-to-metal sealing |
|
Welding Compatibility |
Laser welding heat-affected zone width <0.2mm; post-weld 540°C annealing eliminates microcracks |
Aerospace sensor hermetic sealing |
Application
- Electronics Industry
Sealing and encapsulation with hard glass or ceramics for transistors, integrated circuit lead frames, relay housings, etc., ensuring high hermetic integrity (e.g., high-frequency power transistors, X-ray tube bases).
- Precision Instrumentation
Manufacturing dimensionally stable components such as precision balance beams, watch compensation parts, and microwave waveguides.
- Cryogenic Engineering
Sealed structures for liquid oxygen/hydrogen storage tanks, transfer pipelines, and deep-space exploration equipment, with temperature resistance down to -196°C (requiring specialised processing).
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