Expansion Alloy 4J28 Strips: Glass-Seal Expansion Matching and Corrosion Resistance

Product Overview

Expansion Alloy 4J28 Strips (Alloy 27) are precision-rolled iron-chromium strips formulated to closely match the coefficient of thermal expansion of typical soft sealing glasses, ensuring hermetic, stress-free bonds between metal and ceramic or glass. Between – 50 °C and 400 °C, 4J28 exhibits a mean linear expansion coefficient of approximately 4–8 × 10⁻⁶ /°C, minimizing thermal stresses in glass-to-metal seals. The alloy’s robust chromium-rich matrix (27–29 % Cr) and low carbon, phosphorus, and sulfur (≤ 0.12 % C; ≤ 0.02 % P, S) confer excellent corrosion resistance in mild atmospheres and compatibility with sealing glasses. Standard strip dimensions cover 0.2 – 3.5 mm thickness (cold-rolled) and up to 300 mm width; larger widths and thicknesses via hot-rolling/forging can accommodate broader applications. 4J28 Strips are engineered for reliable sealing in vacuum tubes, hermetic feedthroughs, glass-encapsulated sensors, and precision electronic packages, where dimensional stability and corrosion resistance are paramount. Their formability allows tight-tolerance bending and stamping without springback, while weldability supports complex assembly. For full mechanical property data—tensile, yield, hardness—and thermal-conductivity curves, please consult primary alloy producers like Special Metals (Invar/Glass alloys), Rolled Alloys (precision strip), and Haynes Intl.

Chemical Composition

Mechanical Properties

Physical Properties

Conformance Standards

• AMS 4951 – Iron-chromium low-expansion alloy

• DIN 17 327 – Nickel-iron sealing alloys

• ISO 464 – Glass-to-metal sealing alloys

Applications

• Vacuum & Electronic Seals – Glass-to-metal feedthroughs, vacuum tubes, hermetic connectors

• Precision Instruments – Pressure sensors, gas discharge tubes, photomultiplier bases

• Ceramic Package Encapsulation – Sealing of ceramic circuit substrates to metal headers

• Thermomechanical Assemblies – Bimetallic thermostats, expansion joints

• Medical Devices – Hermetic seals in implantable electronics and sensors

Frequently Asked Questions

Q1: What makes 4J28 Strips ideal for glass-to-metal seals?
A1: Their thermal expansion closely matches soft glass (4–8 × 10⁻⁶ /°C), eliminating stress and preventing seal cracks during thermal cycling.

Q2: Can 4J28 Strips be welded or brazed to other alloys?
A2: Yes—standard electron-beam and laser welding, plus active brazing alloys, bond 4J28 to Kovar, stainless, and nickel alloys without compromising expansion matching.

Q3: Where can I get certified mechanical data?
A3: For certified tensile, yield, hardness, and thermal conductivity data, consult the technical bulletins from Special Metals (Alloy 27), Rolled Alloys, and Haynes International.

Wuxi Nickel New Material Co., Ltd. is a high-tech enterprise integrating the production, manufacturing, and research & development of specialty alloy materials. Located in Wuxi, Jiangsu Province, the company specializes in precision alloys, titanium alloys, high-temperature alloys, corrosion-resistant alloys, heat-resistant steels, nickel-based welding wires, and other specialty materials, with an annual production capacity of 5,000 tonnes. Our product range includes plates, bars, wires, and strips, which are widely used in industrial electric furnaces, power‐station boilers, petrochemical plants, aerospace, marine engineering, machinery, and electronic instrumentation. These materials are characterized by high electrical resistance, high‐temperature strength, corrosion resistance, wear resistance, and fatigue resistance. We can manufacture in compliance with national, industry, and international standards, and are also able to tailor products to meet specific customer requirements.
The company is committed to improving and enhancing its production infrastructure all year round, with a full range of production and processing equipment including vacuum smelting, hot processing, cold processing, and heat treatment. It also has various physical and chemical analysis testing facilities such as spectrometers to ensure product quality. The company has a high-quality R&D, production, and management team that is fully capable of meeting the complex requirements of the current market for material diversification, refinement, and functionalization. Our company is particularly skilled in developing and producing "specialized materials" that are suitable for the market and specific customer needs, which will be one of our company's characteristics. The company adheres to the business philosophy of "guided by market demand, driven by technological progress, and committed to optimizing and innovating materials to create greater value for customers", serving society and the market.