Magnetic properties of materials determine the possibility of their application in various technological processes and devices. In this article we will consider the influence of chemical composition and technological features of heat treatment on magnetic characteristics of precision alloys. Special attention will be paid to structure-sensitive parameters such as coercive force, magnetic induction, magnetic field strength, and hysteresis losses.

Свойства магнитных материалов

Magnetic properties of precision alloys are determined by their chemical composition, manufacturing technology, and heat treatment features. All characteristics acquired by the alloy can be divided into two main groups:

• Structure-insensitive parameters — these include phase transition temperature (Curie point), maximum induction that can be obtained in a certain material (saturation induction), change of volume and linear dimensions of parts depending on their magnetization (magnetostriction). These properties depend on chemical composition and alloy structure and can be adjusted by adding various impurities. Technological features of production and heat treatment have insignificant influence on the listed characteristics.
• Structure-sensitive parameters — these are the strength of the external magnetic field needed for full demagnetization of the material (coercive force), power losses during magnetization and demagnetization of the core when current flows (hysteresis losses), and the coefficient characterizing the relationship between magnetic field strength and magnetic induction (magnetic permeability). These characteristics are substantially influenced by heat treatment and the material production method, as well as presence of harmful and useful impurities. The influence of impurities is linked to the fact that when impurity atoms are introduced, electron density in the crystal lattice is distributed unevenly, and this leads to a change in magnetic properties.

Using various heat treatment methods, structure-sensitive parameters of precision alloys can be substantially changed. For example, magnetic permeability of a material can be increased or decreased in this way by about 20 times.

Influence of carbon and other impurities on magnetic properties of alloys

Carbon is considered one of the most influential impurities. Reducing the amount of this chemical element lowers specific losses and increases magnetic induction of materials, while raising its content worsens magnetic properties of alloys. The figure shows the influence of carbon impurity on iron magnetization curves.

Nitrogen has a more substantial influence on magnetic properties of alloys: even with a slight increase (by 0.005–0.01%) of the percentage content of this substance, coercive force may increase several times. Also coercive force of materials significantly rises when sulfur amount increases, and insignificantly — in presence of phosphorus, oxygen, or manganese. Exactly therefore for precision alloys precise chemical composition and strict control of harmful impurity amounts in the alloy after production are so important.

Role of heat treatment in forming magnetic properties of precision alloys

Mechanical stresses caused by various mechanical processing processes such as rolling and forging introduce substantial changes into magnetic properties. Internal stresses may hinder magnetization, which leads to an increase of coercive force and a decrease of magnetic permeability.

Heat treatment such as annealing plays an important role in restoring magnetic properties after mechanical processing. This process helps relieve internal stresses and create an optimal microstructure of the crystal lattice.

For soft magnetic materials characterized by low coercive force, homogeneity (uniformity) of structure and absence of internal stresses are important. For hard magnetic alloys where high coercive force is required, quenching is used to create magnetic anisotropy — dependence of magnetic parameters on the magnetization direction.

Thus control of composition and application of different mechanical and heat treatment methods play a key role in creating magnetic materials with certain parameters. Understanding the influence of each stage on magnetic properties makes it possible to develop materials with optimal characteristics for specific technological tasks.

PZPS products: main magnetic materials

Petersburg Plant of Precision Alloys releases a whole range of magnetic materials, including those with high magnetic permeability, high saturation induction, a rectangular hysteresis loop, and high magnetostriction. Plant products include alloys of the following grades:

• 50NP and 70NM with a rectangular hysteresis loop;
• 45N and 50N with elevated saturation induction and high magnetic permeability;
• 79NM possessing the highest magnetic permeability in magnetic fields;
• 49K2FA with high saturation induction;
• 49K2F with high magnetostriction.

To order an alloy with the needed magnetic parameters or select an optimal material for implementing your project, leave a request on the website or call the listed phone. Our specialists will answer all your questions in detail and help select the most suitable precision alloy.

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