4J42 Fe-Ni constant expansion alloy is a series of constant expansion alloys which can be matched with soft glass and ceramic with different expansion coefficient in a given temperature range by adjusting the nickel content, and its expansion coefficient and Curie point increase with the increase of nickel content. The alloy is a widely used sealing structural material in the electric vacuum industry, which is used to make soft glass and ceramic matching sealing on electrical components. In the electric vacuum industry and the corresponding soft glass matching sealing. 4J42 also has good corrosion resistance and fatigue resistance, which can be used to manufacture a variety of stressed parts and high-precision measuring instruments. 4J42 is a kind of high performance alloy with excellent performance and wide application. With the continuous development of industrial technology, its application fields will be more and more extensive, and it also needs continuous research and improvement to meet various engineering needs.