Abstract
The changes of the magnetic properties and the microstru ture of high-C high-Cr magnet steel by various heat treatments were investigated, and the origin of the permanent mag etism o this steel was studied. The best magnetic properties (B∼7000 G, Hc∼140 Oe and (BH)max∼0.4×10) are obtained after primary heating and subsequent air-cooling from 1060°. During air-cooling from 1060° many fine spherical carbides which are about 2000 Å in diameter precipitate in the martensite. By primary heating at 600∼900° follow d by air-cooling from 1060°, the quantity of the retained austenite is decreased and the precipitation of the fine carbides promoted. In the case of oil-or water-quenched specimens, dispersion of the fine carbides is supressed. Both Hc and Br of the specimen are increased, whereas the hardness is decreased by the precipitation of the fine spherical carbides. The coercive force of this steel is due to the internal stress in the martensite and also to the magnetization fluctuation of the martensite caused by the precipitation of many fine carbides.
