Introduction
- 4J28(UNS K92801) alloy belongs to the precision alloy series. It is an iron-based, glass-sealing iron-chromium alloy containing 27–29% chromium. Its chemical composition and thermal expansion properties are rigorously controlled to ensure that, within a specific temperature range, its linear thermal expansion coefficient closely matches that of soft glass. This characteristic is crucial in electronic vacuum devices for achieving a reliable, airtight seal between metal and glass.
- Low Thermal Expansion Coefficient:
Within the temperature range of 20–530°C, its linear thermal expansion coefficient is 10.8–11.4×10⁻⁶/K, which is compatible with soft glass (such as soda-lime and borosilicate glass), ensuring effective sealing. - Corrosion Resistance:
The high chromium content gives the alloy excellent corrosion resistance, making it suitable for long-term use in harsh environments.
Chemical Composition
- Cr: 28%
- Fe: Remainder
Alloy Standard
- ASTM: K92801 / Alloy 27 / ASTM F256
- France: LTM
- Germany: FR‑25 / VaCovito25
- UK: croloy27 / 26Cr-Fe
- USA: FR‑28 / Glass Sealing “27” / Carpenter 27 / Alloy 27
- Japan: Cr28
- Russia: 28X
Average Coefficient of Linear Expansion
- 10.8～11.4 10⁻⁶/℃ (20～530°C)
- Heat to 1100±20°C, hold for 15min., cool to room tempreture in the air
Average Coefficient of Linear Expansion
- 20-200℃: 10.0
- 20-300℃: 10.5
- 20-400℃: 10.8
- 20-500℃: 11.1
- 20-600℃: 11.2
- 20-700℃: 11.6
- 20-800℃: 11.6
Application
- Electronic Vacuum Devices: Leveraging its thermal expansion coefficient that closely matches soft glass, the 4J28 alloy is commonly used in electronic packaging, vacuum tubes, displays, and other applications where a reliable metal-to-glass seal is essential.
- Precision Instruments and Cryogenic Engineering: In situations that demand precise thermal matching and excellent low-temperature performance, this alloy shows promising potential.
- Aerospace: The alloy is used in manufacturing satellite sensors, rocket engine controllers, and other components that must withstand extreme temperatures and vibrations.
- Other Fields: Due to its excellent corrosion resistance and unique thermal expansion characteristics, the 4J28 alloy can also serve as a critical material in various specialized equipment and industrial products.
Alloy Forms
- Strip
- Sheet
- Rod / Bar
- Wire
