Please send us your inquiry about the customization of other furnace types or related questions about vacuum furnace. We will reply you immediately. Thank you.
Downloads
All documents in the overview
News & Press
All news at a glance
Request
Send us a message
Email: contact@vacfurnace.com
Tel : +86-21-50878190
Wechat : 2210154395
Address: NO.1299, XinJinQiao Road, Pudong New Area, Shanghai, China.
Do you know the advantages of vacuum annealing of soft magnetic materials?
Introduction to vacuum annealing process of soft magnetic materials
Magnetic materials are widely used in power transmission and transformation equipment, communications, electronic computers, household appliances, automobiles, aerospace and other industrial fields to make electrical and electronic products. According to the difficulty of demagnetizing the material after magnetization, magnetic materials are divided into hard magnetic materials and soft magnetic materials. After hard magnetic materials are magnetized by an external magnetic field, they can still maintain most of the magnetism in the original magnetization direction even under the action of a considerable reverse magnetic field. Soft magnetic materials show strong magnetism after magnetization in a magnetic field, and their magnetism basically disappears after leaving the magnetic field. According to the composition, they can be divided into soft ferrites and metal soft magnetic materials. Metal soft magnetic materials mainly include electrical silicon steel, iron-nickel alloy (Permalloy), amorphous soft magnetic alloy and electrical pure iron.
Reasons for using vacuum annealing process
Whether it is to correct the stress distortion caused by the processing process or to obtain the required organizational structure, soft magnetic materials need to be annealed at high temperature. Vacuum annealing can not only prevent high-temperature oxidation of materials, but also remove impurities such as carbon, oxysulfide and nitride in magnetic materials to the maximum extent, increase the grain size, reduce the uneven state of grain orientation, lattice defects, distortion and other non-uniform conditions caused by cold deformation, and thus improve the performance of magnetic materials. Vacuum annealing is increasingly becoming an important process to improve the performance of soft magnetic materials. Studies have shown that the no-load current of D320 steel strip annealed in vacuum is 8.8% lower than that of air annealing at 15000Gs (1Gs=10-4T, the same below), and the iron loss is reduced by 6.4%.
Advantages of vacuum annealing of silicon steel
Silicon steel is a ferrosilicon alloy with a silicon content of about 3%~5%. It is the most widely used soft magnetic alloy and is mainly used to make iron cores of various motors, generators and transformers. Silicon steel is divided into hot-rolled silicon steel and cold-rolled silicon steel. Hot-rolled silicon steel is gradually being eliminated.
Generally speaking, cold-rolled silicon steel manufacturers have been able to provide cold-rolled silicon steel products with excellent soft magnetic properties through continuous annealing technology. However, production practice and research have shown that in the process of producing electrical products, stamping and cutting will damage the magnetic properties of silicon steel, and this magnetic property damage can be partially restored by vacuum annealing.
Advantages of vacuum annealing of iron-nickel alloy
Nickel can form a variety of iron-nickel soft magnetic alloys (also known as Permalloy) with different magnetic properties in a wide range of 35%~81% with iron, and alloy elements such as molybdenum, copper, chromium, manganese and silicon can also be added to make up for the shortcomings of binary alloys, making Permalloy widely used in power, electronics and communications.
In addition to being related to the composition and impurity content, the magnetic properties of Permalloy are also related to the microstructure of the alloy, such as texture, orientation, and order. Materials with the same composition can show completely different hysteresis loops and different grain structures. The heat treatment process directly affects the performance of these alloys that are sensitive to the organization. Since Permalloy parts are usually small in size, regular in shape, and easy to burn through, there are no special requirements for the heating stage in the process. The process parameters include vacuum degree, annealing temperature, holding time, and cooling method. Generally speaking, the higher the vacuum degree, the more thorough the removal of impurities and gases.
The table below reflects the effect of vacuum degree on the initial magnetic permeability μo of w(Ni)79% and w(Mo)4% alloys.
The higher the vacuum, the better the magnetic properties. However, since the carbon content has the greatest impact on the performance of soft magnetic materials, if there is a lack of oxygen, it is difficult to remove carbon from the material through vacuum alone, and an increase in the degree of vacuum may also cause carbon evaporation and evaporation of components in the vacuum furnace. Nickel evaporation (nickel’s vapor pressure is relatively high) may have the opposite effect.
When studying the effect of heat treatment process on 1J22 alloy, it was found that the alloy surface turned white under the pressure of 7×10-3Pa. Later, it was changed to 7X10-1Pa + argon partial pressure to obtain a bright surface. In addition, element evaporation under excessively high vacuum conditions can also cause workpiece adhesion, which has been reported in the literature. Therefore, the more suitable vacuum degree is 1X10-1~1X10-2Pa.
Vacuum annealing temperature is an important process parameter that affects the performance of magnetic materials. The higher the temperature, the more conducive to the growth of alloy grains. As the grains grow, the number of grain boundaries decreases, the resistance to domain wall movement magnetization decreases, the hysteresis loss decreases, the initial magnetic permeability μ0 increases, and the coercive force Hc decreases and the magnetic properties become better. It should be pointed out that when performing vacuum annealing of related soft magnetic alloys, better magnetic properties may be obtained by making adjustments based on the size and structure of the workpiece.
Vacuum Annealing Furnace