Abstract
The coercive force of quench-hardened magnet steels has hitherto been explained by Becker’s internal stress theory. However, in the light of recent experience with iron and iron alloy, it is likely that stresses play rather a minor role. In this paper the magnetic properties, the Vickers hardness and the magnetic domain patterns of quench-hardened magnet steels (mainly MT magnet steel) were observed.As the results of measurements, it was found that the change of the coercive force is not proportional to that of the Vickers hardness, which is related to the internal stress, and that the coercive force is proportional to the square root of the volume, (1−v), of austenite. The best magnetic properties of quench-hardened magnet steels are obtained, when fine particles of martensite needles are distributed in the nonmagnetic retained austenite and the ratio of martensite to austenite is 2 to 1.
