Due to dominant trends in the development of various industries in recent decades, demand for new magnetic materials has sharply increased. The need for them intensified around the mid-1990s and continues to grow. Transformers, magnetic amplifiers, rotors and stators of electrical machines, and much more — all of this requires components produced from soft magnetic alloys. So what are they?
From the school physics course it is known that the magnetic properties of all materials make them react in one way or another to a magnetic field. In the world around us most materials are diamagnets or paramagnets, i.e. they almost do not react to a magnetic field. However, there are also so-called ferromagnets — materials able to magnetize under an external magnetic field and partially or fully retain the acquired magnetization after removal from it. First of all these are metals: if you run a permanent magnet over a nail or screwdriver, these objects temporarily magnetize and will emit their own weak magnetic field.
The most common ferromagnets are iron, cobalt, and nickel, but in everyday life we rarely encounter chemically pure substances. In producing metal products special alloys are usually used to give the metal specified properties — sensitivity, wear resistance, and so on. Thus compounds based on iron, cobalt, or nickel with addition of manganese, silicon, aluminum, and other materials can give rise to various kinds of precision alloys that demonstrate ferromagnetism and have specified parameters.
Depending on ease of magnetization, ferromagnets divide into hard magnetic and soft magnetic. Soft magnetic materials (and alloys created from them) magnetize easily, but this magnetism is usually temporary. Hard magnetic ones, conversely, magnetize with difficulty but then retain their magnetism.
Products from precision soft magnetic alloys have high strength and adequate ductility, withstand high current, have a temperature coefficient of linear expansion, and have good magnetic properties. Such characteristics are needed to manufacture especially sensitive elements and high-precision instruments. Computers, microphones, radios, antennas, microscopes, and many other important objects could not fully perform their functions without using various kinds of soft magnetic alloys in their manufacture.
Each grade serves to produce products with different properties. For example, alloys grade 50NKhS are used in cores of communications apparatus chokes and pulse transformers; grade 49K2F — in ultrasonic and hydroacoustic apparatus, electromechanical filters, delay lines; and 49K2FA — in telephone diaphragms.
To decode an alloy grade one must know which letters conventionally denote which chemical elements in the product composition. If the letter A stands at the very end, it means this is high-quality steel; phosphorus and sulfur content in it is minimized, and all conditions of high-quality metallurgical production are observed. Two letters A at the very end indicate that this steel grade is especially pure, i.e. there is practically no sulfur and phosphorus in it. Ordinary-quality steels are denoted by the letter “t” and digits from 0 to 6, which denote the grade number depending on its chemical composition and mechanical properties.
Steel grade 79NM means the base of the metal alloy is nickel (Ni); its content may range from 78.5% to 80%. And in alloy grade 50N nickel is from 49% to 50.5% (i.e. in this case the letter N denotes nickel).
It is not necessary to memorize all alphanumeric designations — to clarify information on a specific steel grade one can use so-called grade handbooks, which are easy to find on the internet.
