Measurement of magnetic properties of steel at high temperatures

This paper deals with the measurement of the magnetic properties of steel and other soft magnetic, electrical conductive, materials at high temperatures up to the Curie temperature and slightly above. At first the theory of measuring the magnetic properties at room temperature is described on the basis of the ring core method and the Epstein method, since aspects of both are used in the developed measurement setup for high temperatures. The heating of the ring-shaped steel sample is achieved by using it as the secondary, short-circuited winding of a transformer. The ring itself is thermally insulated and wound with two coils, which allow the determination of the magnetic properties. The measurements show that the saturation polarization is decreased a little bit up to 500 °C and then drops to zero at slightly above 700 °C. However the initial permeability is increased with temperature and the iron losses for low polarizations are decreased.