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1. Alloy 4J42 Overview
Looking for a reliable, long-lasting hermetic seal between metal and glass or ceramic? Alloy 4J42 is an iron-nickel controlled-expansion precision alloy engineered to solve the cracking and leakage problems that plague electronic packaging. With a thermal expansion perfectly matched to soda-lime soft glass and alumina ceramics, 4J42 delivers leak-tight, high-integrity seals for decades – even under extreme thermal cycling.
How is 4J42 different from Invar (4J36)? While Alloy 4J36 (Invar) is famous for ultra-low expansion in measuring instruments, 4J42 is purpose-built for sealing. Its nickel content is tightly controlled at 41.5%–42.5%, providing a coefficient of thermal expansion that virtually eliminates residual stress at the sealing interface after cooling – a critical advantage for hermetic electronic packages.
2. Technical Specifications
2.1 Chemical Composition (mass fraction %)
Alloy 4J42 meets the GB/T 15018 standard for controlled-expansion Fe-Ni alloys. A single-phase austenitic structure is maintained across the full service temperature range, and strictly limited sulfur, phosphorus, and carbon prevent brittle interlayers from forming during sealing.
| Element | C | P | S | Mn | Si | Al | Co | Ni | Fe |
|---|---|---|---|---|---|---|---|---|---|
| Max (≤) | 0.05 | 0.020 | 0.020 | 0.80 | 0.30 | 0.10 | 1.0 | 41.5–42.5 | Balance |
2.2 Mechanical Properties
4J42 offers excellent formability for stamping, etching, and deep-drawing, with mechanical strength tailored by condition.
Tensile Strength (Strip)
| Condition Code | Condition | Tensile Strength (MPa) |
|---|---|---|
| S | Soft | < 590 |
| H | Hard | > 700 |
Typical Hardness (Strip)
| Condition | Thickness | Hardness HV |
|---|---|---|
| Deep-drawn | > 2.5 mm | ≤ 170 |
| Deep-drawn | ≤ 2.5 mm | ≤ 165 |
2.3 Thermal Expansion Characteristics
After standard heat treatment (hydrogen atmosphere, 900 °C ± 20 °C for 1 hour, cooled at ≤ 5 °C/min to below 200 °C), the alloy meets these guaranteed expansion ranges:
Mean Coefficient of Linear Expansion (Specification)
| Temperature Range | α (10⁻⁶ / °C) |
|---|---|
| 20–300 °C | 4.0 – 5.0 |
| 20–450 °C | 6.5 – 7.5 |
Representative Linear Thermal Expansion (Typical Data, α in 10⁻⁶ / °C)
| 20–100 °C | 20–200 °C | 20–300 °C | 20–400 °C | 20–450 °C | 20–500 °C | 20–600 °C |
|---|---|---|---|---|---|---|
| 5.6 | 4.9 | 4.8 | 5.9 | 6.9 | 7.8 | 9.2 |
3. Key Performance Advantages
- Thermal expansion matched to glass and ceramics
Ordinary steels and stainless steel have CTEs far from most sealing glasses, leading to microcracks after cooling. 4J42 leaves almost zero residual stress at the seal interface. After tens of thousands of thermal cycles, the seal remains intact – maintaining vacuum or inert gas containment for decades. - Strong oxide film adhesion for permanent hermeticity
A dedicated pre-oxidation process creates a thin, uniform oxide layer that bonds thoroughly with molten glass without brittle intermetallics. This is a core advantage unique to sealing-grade alloys like 4J42, and it’s not achievable with non-sealing low-expansion alloys such as 4J36. - Ultra-clean for vacuum and semiconductor environments
Extremely low volatile impurity content means no outgassing during high-temperature bake-out. It won’t contaminate silicon wafers, optical chips, or vacuum chambers – essential for TO-header encapsulation and other high-cleanliness processes. - Excellent electroplating and chemical etching compatibility
After annealing, the surface is smooth and uniform, making it ideal for stable electroplating of nickel, gold, or tin with strong adhesion. It is compatible with mild alkaline cleaning and precision etching, simplifying downstream component fabrication.
4. Heat Treatment Processes
4.1 Annealing
Heat to approximately 1100 °C to improve ductility and workability for further forming.
4.2 Low-Temperature Stress Relief (for cold-worked parts)
After stamping, etching, or wire drawing, hold at 600–650 °C for 30–90 minutes and cool slowly. This relieves machining stresses without altering the expansion coefficient, preventing slow distortion or leakage during long-term storage.
4.3 Pre-Oxidation for Glass Sealing (essential for 4J42)
Prior to sealing, parts are held in a wet hydrogen atmosphere at 900 °C for 30–60 minutes. This generates the optimal oxide layer for glass bonding, dramatically improving the metal-to-glass bond strength. This step is a must in optoelectronic and vacuum device production.
5. Forming and Welding
Alloy 4J42 is readily processed by cold rolling, hot rolling, wire drawing, and stamping. It also exhibits good weldability, allowing reliable joining to other metals and glass materials – ideal for precision hermetic packaging assemblies.
6. Main Application Areas
6.1 Semiconductor & Optical Communications Packaging (core use)
TO-CAN laser headers, ceramic IC package bases, MEMS pressure sensor pedestals, photodiode lead frames, relay sealed pins, and glass-sealed vacuum tube components.
6.2 Microwave & Vacuum Electronic Devices
CRT lead-out wires, microwave tube sealing rings, vacuum capacitor metal bases, and insulating seals for electron beam equipment.
6.3 Industrial Precision Sensors & Instruments
Temperature/pressure sensor housings, instrument glass sealing bushings, and sealing supports for compact optical devices.
6.4 Aerospace Airborne Electronic Components
Satellite signal transmission sealed housings, airborne precision sensor bases, and aerospace relay hermetic structures – engineered to withstand wide temperature swings and continuous vibration without interface leakage.
7. Sourcing 4J42 from C&N
Selecting the right supplier depends on technical capability, quality control, and reliable delivery. C&N is an experienced pipe and alloy product manufacturer with deep expertise in 4J42 production. We supply a wide range of specifications and offer:
- Custom dimensions and performance tuning
- Rapid technical response for special requirements
- Tailored production solutions
If you are engineering a glass-to-metal seal or ceramic package and need a reliable controlled-expansion alloy, contact us today to discuss your project. Our team is ready to provide a quick technical evaluation and a competitive quotation.
