Magnetic Materials Vacuum Heat Treatment Process

The raw materials of soft magnetic alloys are mainly rods, strips and plates, etc. The parts are cut, punched, punched or rolled by cold working. During the processing, the original grain structure of the material will be destroyed, which will reduce the magnetic permeability of the material. At the same time, the processing stress generated during the processing will lead to the instability of the size of the part. Therefore, the parts made of soft magnetic alloys must be annealed after processing, so that the material can regain a regular equiaxed grain structure, reduce the impurity content in the material, restore and improve the magnetic properties of the material, and eliminate the processing stress at the same time. Stable part size. According to different materials and application requirements, the annealing of soft magnetic alloy parts can be annealed at high temperature (1150-1250 ℃) and medium-temperature annealing (800-850 ℃). Among them, permalloys with high magnetic permeability are usually annealed at high temperature, and sometimes magnetic field annealing is used to further improve the magnetic permeability. ) is annealed at medium temperature.

Before there was no vacuum furnace, many manufacturers used a well-type externally heated atmosphere furnace, which was treated by nitrogen or hydrogen protection. This treatment method has obvious defects, especially when nitrogen is used as the protective atmosphere. First of all, when nitrogen protection is used, the purity of the atmosphere obtained by nitrogen replacement in the furnace is not enough, and the flow direction of nitrogen has a great influence on the surface quality of the workpiece, and the color of the same furnace parts after treatment is often inconsistent. This is due to the presence of areas in the furnace where nitrogen flow is not smooth, and some workpieces are slightly oxidized. Secondly, the temperature uniformity of the external heating furnace is poor, the performance of the treated parts varies greatly, and the pass rate is low. In addition, in terms of energy consumption, the lining of the external heating furnace is thick, the power consumed on the lining during the heating process is large, and the thermal efficiency is low; in the heating process, high-purity nitrogen needs to be continuously charged, and the nitrogen consumption is large; heat-resistant steel The service life of the furnace retort at high temperature is low, which leads to the high operating cost of the externally heated furnace. If hydrogen is used as the protective atmosphere, the performance and surface quality of the workpiece can be improved by relying on the strong decarburization ability and reducing effect of hydrogen, but the problems of uneven temperature and high operating cost are still inevitable. The use of internal heating vacuum annealing furnace is of great significance to the annealing of soft magnetic alloy parts. The internal heating vacuum furnace has obvious advantages in terms of workpiece processing effect, operating cost, production efficiency and production environment.

Most of the parts made of hard magnetic alloys are formed by powder metallurgy, and then solution treatment or annealing is performed, so the heat treatment of hard magnetic material workpieces is mainly vacuum sintering, vacuum solution treatment and vacuum annealing. Due to the strict control of carbon content for NdFeB and AlNiCo alloy materials, molybdenum sheets should be used for hard magnetic alloy parts, whether sintering or solution treatment, heating elements and reflector screens of vacuum furnaces.

Hard magnetic alloy parts are punched or extruded in a die after mixing powder and adhesive evenly. During the sintering process, due to the existence of the binder, the workpiece will have a peak of outgassing between 300 and 600 °C, and a second peak of outgassing will appear between 900 and 1000 °C [3] . Therefore, the vacuum furnace used for hard magnetic alloy sintering should be equipped with a diffusion pump with a large pumping speed to avoid oxidation. Hard magnetic alloy parts are punched or extruded in a mold after mixing powder and binder uniformly. During the sintering process, due to the existence of the binder, the workpiece will have a peak of outgassing between 300 and 600 °C, and a second peak of outgassing will appear between 900 and 1000 °C [3] . Therefore, the vacuum furnace used for hard magnetic alloy sintering should be equipped with a diffusion pump with a large pumping speed to avoid oxidation.

After sintering and forming of hard magnetic alloy parts, some need to be treated by solution treatment to make the composition of the material uniform and the structure stable, so as to improve its permanent magnetism. Since the solution treatment has certain requirements on the cooling rate (> 100 ℃/min), the solution treatment can be carried out in a molybdenum sheet-type pressurized gas quenching furnace.

Editor: Frank Lee

Copyright: SIMUWU Vacuum Furnace