Heat treatment of soft magnetic alloy to achieve excellent performance of a key process. By controlling the heating temperature, holding time, cooling speed and cooling mode, it changes the internal structure and magnetic structure of the alloy in a certain heating medium to obtain the required magnetic properties. The heat treatment of soft magnetic alloy includes high temperature annealing and magnetic field heat treatment.
(1) high temperature annealing. The aim is to eliminate the processing stress, remove the nonmetallic inclusions harmful to the soft magnetic properties, recrystallize and grow the grains evenly, and form the grain orientation. There are two kinds of high temperature annealing: hydrogen heat treatment and vacuum heat treatment. To change the degree of order of soft magnetic alloys during the order - disorder transition, the magneto-crystal anisotropy constant K1 and the magnetostrictive coefficient lambda s are adjusted to get better magnetism, usually by controlling the cooling rate or changing the insulation time below Tc.
(2) magnetic field heat treatment. Some soft magnetic alloys can form uniaxial induced magnetic anisotropy and texture after heat treatment, thus changing the magnetization behavior of the alloys. Especially for alloys with small magnetic anisotropy, the induced magnetic anisotropy plays a major role. For example, 65% ni-fe alloy, K1≈0 under slow cooling condition, has a rectangular hysteresis loop when measuring magnetism along the direction of external magnetic field after magnetic field heat treatment. The hysteresis loop is flat when measured in the direction perpendicular to the applied magnetic field. There are two systems of magnetic heat treatment. One is to heat the alloy to a temperature just above Curie and then cool it in a magnetic field. The other is heat treated with a magnetic field at a temperature slightly below Curie. Magnetic fields are also applied in two ways: vertically and horizontally. The direction of the former magnetic field is consistent with the direction of magnetization in the working process of the material, while the latter is perpendicular to each other.