4j29 Imported Precision Alloy High Magnetic Permeability Iron-Nickel Alloy Kovar Material Properties

4J29
4J29 alloy is also called Kovar alloy. The alloy has a linear expansion coefficient similar to that of borosilicate hard glass at 20-450°C, a higher Curie point, and good low-temperature structural stability. The oxide film of the alloy is dense and can be well wetted by glass.  It is the main sealing structure material of electric vacuum devices

Application overview and special requirements
 The alloy is a typical Fe-Ni-Co hard glass sealing alloy used internationally. It has been used by aviation factories for a long time and has stable performance. It is mainly used for glass sealing of electric vacuum components such as launch tubes, oscillating tubes, ignition tubes, magnetrons, transistors, sealing plugs, relays, lead-out wires of integrated circuits, chassis, shells, brackets, etc. In the application, the selected glass should match the expansion coefficient of the alloy. Its low-temperature tissue stability is strictly tested according to the use temperature. Appropriate heat treatment should be carried out during processing to ensure that the material has good deep drawing and drawing properties. When using forgings, their airtightness should be strictly checked.

Alloy structure
After the alloy is treated according to the heat treatment system specified in 1.5, it is then frozen at -78.5°C, and martensite should not appear for 4 hours or more. However, when the alloy composition is inappropriate, different degrees of austenite (γ) to acicular martensite (α) transformation will occur at room temperature or low temperature, and the phase transformation is accompanied by volume expansion effect. The expansion coefficient of the alloy increases accordingly, resulting in a sharp increase in the internal stress of the seal, and even causing partial damage. The main factor affecting the microstructure stability of the alloy at low temperature is the chemical composition of the alloy. It can be seen from the Fe-Ni-Co ternary phase diagram that nickel is the main element to stabilize the γ phase, and a high nickel content is conducive to the stability of the γ phase. As the total deformation rate of the alloy increases, its microstructure tends to be more stable. Alloy composition segregation may also cause γ→α phase transformation in local areas. In addition, coarse grains will also promote the γ→α phase transformation.

Chemical composition

C	Mn	Si	P	S	Cu	Cr	Mo	Ni	Co	Fe
								28.5	16.8
0.03	0.5	0.30	0.020	0.020	0.20	0.20	0.20	29.5	17.8	allowance

Under the condition of average linear expansion coefficient reach standard, allow the content of nickel and cobalt deviate from the prescribed scope. Aluminum, magnesium, zirconium and titanium content is more than 0.10%, the total amount should be no greater than 0.20%.