Analysis on heat treatment process of high frequency induction heating equipment for beryllium bronze film parts

A beryllium bronze diaphragm (wall thickness ≤ 0.06mm) used for a special instrument is heated and quenched by high-frequency induction heating equipment in an ammonia decomposition atmosphere, (770+10) ℃ x7min water cooling, surface defects of bubbles and pimples often appear, often causing workpiece Scrap, seriously affecting product production.

For beryllium bronze bubble defects, the current views are relatively consistent, and it is believed to be caused by poor deoxidation during material smelting. The morphology feature is a typical bubble-type defect with convex on both sides and a cavity inside. The metallographic observation of papule defects shows that the surface is raised, and there is a small bright area in the center of some parts, and a dark circle area on the periphery. Scanning electron microscope observation revealed that it was densely covered with elongated spherical protrusions, accompanied by some cavities exposed after the surface swelled, and there were traces of surface plastic deformation developing to tearing locally. Beryllium copper ammonium decomposition protection The pimples generated by the high-frequency induction heating equipment after heating and quenching are actually tiny bubbles.

The test analysis shows that the gas contained in the material is one of the causes of bubbles in the workpiece. When the beryllium bronze film is heated and quenched by high-frequency induction heating equipment in an ammonia decomposition atmosphere, hydrogen is the main cause of surface papules. When the beryllium bronze diaphragm is heated in an ammonia decomposition atmosphere, under high temperature and atmospheric pressure, a part of the hydrogen atoms are adsorbed on the surface of the diaphragm, diffuse inward along the grain boundaries and dislocations, and gather in the dislocation lines and grains where the stress is concentrated. boundaries and holes. Hydrogen atoms form hydrogen molecules, generating huge internal stress. Under stress, the diaphragm deforms, forming surface bulges or even surface ruptures at the weakest point. This is the main reason for the formation of papules on beryllium bronze diaphragms. Tests and analysis found that only very thin workpieces with a thickness of about 0.04mm are prone to papule defects. When the thin film is heated by high-frequency induction heating equipment, the two outer surfaces absorb hydrogen atoms and diffuse at the same time, which is easy to accumulate in certain dislocations and holes in the material.

According to the above analysis, it can be seen that preventing the infiltration of hydrogen and forming an oxide film on the metal surface is an effective method to avoid papule defects in the diaphragm. Tests have shown that preoxidation at 320°C±10°C for several minutes can prevent the formation of pimples on the surface of the diaphragm. This is due to the oxidation-reduction reaction between the oxide film and hydrogen, copper oxide is reduced to copper, attached to the surface of the diaphragm, and hydrogen oxidizes to generate water vapor to escape. In this way, on the one hand, the oxide film blocks the infiltration channel of hydrogen, and on the other hand, it reduces the instantaneous partial pressure of hydrogen on the surface of the diaphragm, effectively preventing the chloroform and butyl from entering the diaphragm metal. After heating at 320°C with the help of high-frequency induction heating equipment, the internal stress caused by processing is reduced, the stress at the dislocation line and hole defect is reduced, the microscopic hole is welded, and the degree of hydrogen concentration is reduced, which can effectively prevent the film Pimple defects formed on the tablet surface.

After pre-oxidation treatment at 320°C ± 10°C for several minutes during production, a very thin layer of oxide film (thickness ≤ 0.001mm) is formed on the beryllium bronze diaphragm, which can effectively prevent the formation of papules on the surface of the workpiece. Production practice shows that papules The rate is less than 3%.