Magnets that can maintain their magnetism for a long time are called permanent magnets. Such as natural magnets and artificial Magnetic Steel. Permanent magnets are hard magnets, which are not easy to lose magnetism and are not easy to be magnetized. The materials used as magnetic conductors and electromagnets are mostly soft magnets. The polarity of the permanent magnet does not change, while the polarity of the soft magnet changes with the polarity of the applied magnetic field.
A permanent magnet is an object that can retain a certain residual magnetization after the external magnetic field is removed. To make the residual magnetization of such an object zero and the magnetism completely eliminated, a reverse magnetic field must be added. The magnitude of the reverse magnetic field required to completely demagnetize the ferromagnetic substance is called the coercivity of the ferromagnetic substance. Both steel and iron are ferromagnetic, but their coercive force is different. Steel has a larger coercive force, while iron has a smaller coercive force. This is because in the steelmaking process, carbon, tungsten, chromium and other elements are added to iron to make carbon steel, tungsten steel, chromium steel, etc. The addition of carbon, tungsten, chromium and other elements causes various inhomogeneities in the steel at room temperature, such as uneven crystal structure, uneven internal stress, and uneven magnetic strength. These uneven physical properties all increase the coercive force of steel. And the greater the degree of unevenness within a certain range, the greater the coercive force. However, these inhomogeneities are not the best state that steel has or has reached under any circumstances. In order to achieve the best state of internal inhomogeneity of steel, proper heat treatment or machining must be carried out.
Steel or other materials can become Permanent Magnet Components because after they are properly processed and processed, the internal unevenness is in the best state and the coercive force is the largest.