Abstract
A guide for the heat treatment of Si-Fe alloys containing up to 3.9%Si being used as various core materials was presented from the practical point of view. It was found that magnetic properties in Si-Fe alloys containing more than about 2.5%Si are considerably affected by the cooling rate during the heat treatment and improved by a rapid cooling. The rapid cooling effect expressed as the percentage increase of the magnetic quantities such as maximum permeability or B0.5 at intermediate fields depends on the purity of specimens and the operating temperature. The effective cooling rate is below 40 min which is the time taken to cool from 800°C to 200°C. The greater the cooling velocity, the more excellent magnetic properties are obtainable when other conditions than above-mentioned are appropriate, except that the heat stress is generated in the specimens by quenching. As the method, air-quenching and oil-quenching were undertaken in this work. The excellent properties thus obtained were not so changed by aging treatment at 100°C for a long time, but were notably deteriorated at 150°C.
From the above considerations and the results obtained by micrographic observation, it seems reasonable to interpret that the rapid cooling effect is due to the interstitial impurities such as C and N which are dissolved at higher temperatures and frozen at room temperature by rapid cooling from the high temperature; if the specimens are slowly cooled or aged, these impurity elements probably precipitate as non-magnetic inclusions, and consequently are always deterimental to this effect.
