What is 4J52 alloy ?


4J52, also known as iron-nickel fixed expansion alloy, is a member of a series of fixed expansion alloys. Fixed expansion alloys have the ability to match the expansion coefficients of soft glasses and ceramics over a specific temperature range by adjusting the nickel content. Increasing the nickel content increases the expansion coefficient and Curie point of the alloy. 4J52 alloy is widely used in sealing structural materials in the electric vacuum industry.

Chemical composition of 4J52 alloy






















Mechanical properties of 4J52 alloy

Status code


Tensile strength of 4J52 wire,N/mm2


soft state



hard state


Status code


Tensile strength of 4J52 strip,N/mm2


soft state



hard state


Average linear expansion coefficient of 4J52 alloy


Sample heat treatment system

Average linear expansion coefficient a,10-6/




Heat to 850±20  in a hydrogen atmosphere and keep warm for 1 hour.

Cool to below 200  at a speed of no more than 5 /min and come out of the oven

20~ 300

20~ 400 

20~ 450

 9.8~ 11.0

 9.81~ 11.0


Heat treatment of 4J52 iron-nickel fixed expansion alloy

Heating stage: Place the 4J52 alloy sample in a protective atmosphere or vacuum environment.

Heating temperature: Heat the sample to 850℃±20℃.

Holding time: The specimen is kept at a temperature of 850℃±20℃ for 1 hour to ensure thermal equilibrium and tissue stabilization.

Cooling phase:

Cooling rate: When the sample is cooled from 850°C to a temperature below 400°C, the cooling rate should not exceed 300°C/minute.

Cooling medium: This process is usually carried out in air.

The main purpose of heat treatment is to improve the structure and properties of 4J52 alloy to achieve specific expansion coefficient requirements. Through the heating and holding stages, the grains in the alloy realign and eliminate internal stresses, thereby improving the material’s stability and expansion properties. The control of the cooling stage ensures that the structure and properties of the alloy can be effectively fixed.

Smelting and casting process of 4J52 iron-nickel fixed expansion alloy

The smelting and casting process of 4J52 iron-nickel fixed expansion alloy mainly adopts one of the following methods:

Non-vacuum induction furnace melting: smelting in a non-vacuum environment. Non-vacuum induction furnaces use the principle of electromagnetic induction to heat and melt materials.

Vacuum induction furnace melting: Melting is carried out in a vacuum environment to reduce gas and impurity pollution. Vacuum induction furnaces combine induction heating and vacuum technology to effectively control the melting process.

Electric arc furnace melting: Using an electric arc to heat and melt materials. Electric arc furnaces can provide high-temperature and high-energy melting conditions.

The selection of the above smelting methods depends on the specific production equipment and process requirements. Each method has its advantages and scope of application. During the smelting process, attention should be paid to controlling the smelting temperature, time and material composition to ensure the required alloy composition and quality.

The casting process includes steps such as mold preparation after smelting, pouring of molten alloy, and cooling and solidification. The specific casting process is selected and optimized based on the casting shape and size, as well as the required performance and quality.

Application overview of 4J52 iron-nickel fixed expansion alloy

4J52 iron-nickel fixed expansion alloy is mainly used in the following aspects:

Sealing with soft lead glass: 4J52 alloy has long been used for sealing with soft lead glass in aviation factories and other fields. Soft lead glass is a sealing material that matches the expansion coefficient of 4J52 alloy and can maintain good sealing performance during thermal expansion and contraction, ensuring that the packaged components are not affected by the external environment.

Small electronic tube leads: 4J52 alloy is also commonly used to manufacture the leads of small electronic tubes. In electronic devices, leads usually carry out the transmission and connection functions of electronic signals. Since 4J52 alloy has stable performance and appropriate thermal expansion coefficient, it can provide reliable lead materials during the manufacturing process of small electronic tubes to ensure the stability and reliability of signal transmission.

In general, 4J52 iron-nickel fixed expansion alloy plays an important role in aerospace factories and electronic manufacturing through its application in soft lead glass sealing and small electronic tube leads. Its stable performance and matching properties with sealing materials make it a reliable material choice.

Precautions when using 4J52 alloy

When using 4J52 alloy, you need to pay attention to the following matters:

Select the appropriate sealing material: In order to ensure a good sealing effect, the selected sealing material should match the expansion coefficient of the 4J52 alloy. This can avoid excessive stress during thermal expansion and contraction and ensure the firmness and sealing of the seal.

Control the heat treatment process: Heat treatment is an important link in the preparation process of 4J52 alloy. During heat treatment, the grain size of the alloy should be controlled to ensure that the material has good deep drawing properties. Proper heat treatment can improve the mechanical properties and processing properties of the alloy.

Test the air tightness of the material: When using forging, rolling and other processing methods, the air tightness of 4J52 alloy needs to be strictly tested. Ensure that the alloy material has no obvious pores, inclusions and other defects to ensure the quality and reliability of the product.