One of the main application areas of deformable hard magnetic alloys is production of permanent magnets. In the article we will consider which steels are used in this industry and what properties they have.
Steels based on Fe-Ni-Al and Fe-Co-Ni-Al systems belong to the group of precipitation-hardening materials manufactured by precipitation hardening. This production method implies artificial “aging,” during which a supersaturated solidified solution after annealing undergoes thermomagnetic treatment. This makes it possible to distribute particles of strongly and weakly magnetic phases in accordance with the directions of applied magnetic fields.
Magnets from the presented alloys such as 20NYu, 22NYu, 24KNYu, and others have high strength and ductility. They are used in producing electric motors, electrical measuring devices, and radio equipment.
Cobalt-platinum materials have the highest ductility. They are suitable for manufacturing parts of any configuration and sizes, including wire or foil several microns thick. Due to high cost they are mainly used to manufacture miniature and ultra-miniature magnetic systems. Heat treatment of the material to a high-coercivity state is performed not at its release but during manufacture of the required equipment elements.
Iron-palladium and iron-platinum materials also have high magnetic properties and ability for cold deformation. At the same time cold deformation can be applied not only to change metal sizes and shapes but also to impart the required magnetic properties to it.
Iron-cobalt-vanadium alloys such as 52KFA, 52KFB, 52KFV, and 52KFTM are used to produce small-size magnets. They are released as wire of diameters from 0.5 to 3.0 mm, strips and bands of thickness from 0.2 to 1.3 mm and width not more than 20.1 mm.
Steels of type 52KF belong to materials whose magnetic properties are formed during cold deformation. At the same time magnetic qualities of wire significantly exceed characteristics of sheet metal. This is due to difference of structures and difference of the stressed state during deformation.
Alloy 12GN is released as cold-rolled sheets or strips 0.8 mm thick. After tempering it retains high ductility and can undergo additional mechanical processing, including repeated cold deformation.
Cunico alloys based on the Cu-Ni-Co system and kinife based on Cu-Ni-Fe magnetize easily, while distribution of magnetic axes coincides with the deformation direction. They have high coercive force and crystallographic structure. Manufactured as strips, sheets, and wire. Used to produce permanent magnets, as well as magnetic recording carriers.
Iron-chromium-nickel materials such as 36NKhTYu have elevated ductility and a high degree of rectangular hysteresis loop. Used to create small-size permanent magnets intended for use under extreme climatic conditions and subject to various mechanical loads (impact, vibration, etc.). Also used to produce elements with specified magnetic hardness. Manufactured as wire of diameter from 0.2 to 2.0 mm or cold-rolled strip of thickness from 0.005 to 1.0 mm.
Metals based on the Mn-Al system are characterized by high coercive force, low oxidizability, corrosion resistance, and low specific weight. They machine well. To raise magnetic properties cold deformation is used, as well as alloying the metal with iron, cobalt, titanium, molybdenum, or carbon.
Precision alloys based on Mn-Ca have good ductility, low residual induction, and high coercive force. Maximum magnetic properties are achieved by preliminary cold deformation and final annealing at 450°C.
High-carbon materials based on the Fe-Al-C system, to achieve the required magnetic properties, are subjected to cooling at a critical rate and subsequent tempering. Such precision alloys may be alloyed with chromium and molybdenum. Despite presence of carbon these materials readily undergo hot deformation at 1180–1200°C and mechanical processing. Used in low-power magnetic systems, including measuring instruments and DC motors.
