Magnetic materials are used across industries. Electrical and radio engineering, electronics, instrument making, computer technology, marine, aviation and space navigation, geophysical mineral exploration methods, automation and telemechanics today are unthinkable without hard and soft magnetic alloys. Magnetic flaw detection and magnetic inspection methods are also widely used. Magnetic materials go into making magnetic circuits of generators, motors, transformers, relays, magnetic amplifiers, magnetic memory elements, compass needles, magnetic recording devices, and more.
In an article describing general magnetic properties of substances, we established that ferromagnets, depending on ease of magnetization, divide into soft magnetic and hard magnetic. Products from soft magnetic precision alloys magnetize easily, but this magnetism is usually temporary.
Hard magnetic alloys are precision alloys with predetermined technical parameters and a high magnetism value. In other words, they are hard to magnetize but then retain their magnetism. They are used to make permanent magnets for various apparatus, electromagnetic recording devices, TV focusing devices, microphones, electrical measuring instruments, microelectronics, microwave devices, and other equipment.
Compared with DC electromagnets, hard magnetic alloys have a number of advantages, for example higher performance, savings of materials and energy consumption, and economic and technical benefits of use.
To obtain high coercivity (the external magnetic field strength needed for complete demagnetization) in producing hard magnetic precision alloys, besides choosing chemical composition, technologies that optimize crystal structure and hinder remagnetization are used — quenching steels to martensite, precipitation hardening of alloys, creating high internal mechanical stresses, foreign inclusions at high magnetostriction, and others. As a result, domain wall displacement processes are hindered. In high-coercivity alloys magnetic texture is created by cooling them in a strong magnetic field.
The most important constituents for hard magnetic alloys are iron, nickel, and aluminum. Fe-Ni-Al alloys are not used without alloying elements because of relatively low magnetic properties. The most common are alloys alloyed with copper and cobalt.
To decode alloy composition, grade handbooks are used — databases with detailed systematized information on steel and alloy properties. There one can find information on purpose, classification, substitutes, chemical composition, critical-point temperatures, and physical, mechanical, technological, and casting properties of various steels and alloys.
