High-temperature Magnetization Characteristics of Steels

A method was developed for the measurement of BH curves for steels from room temperature to the Curie point (Tc). A closed magnetic circuit measurement was applied to obtain accurate temperature-dependent magnetic characteristics. BH curves were successfully measured at temperatures over 473 K (200 degrees C), which was not possible before the development of this method.& para;& para;In addition, at room temperature BH curves measured by the proposed method and a conventional method correspond well, which indicates the validity of the proposed method.& para;& para;In the measurement for a medium-carbon steel and a electromagnetic soft iron, the difference in the magnetic flux density at 8 000 A.m(-1) (B-8k) came from the low saturation magnetic flux density of cementite in the medium-carbon steel. B-8k for the medium-carbon steel clearly decreased as the temperature increased from room temperature to 473 K (200 degrees C), which corresponds to Tc for cementite.& para;& para;In addition, B-8k for the electromagnetic soft iron decreased almost linearly from 973 K (700 degrees C) to 1 048 K (775 degrees C), whereas B-8k for the medium-carbon steel decreased significantly from 998 K (725 degrees C) to 1 023 K (750 degrees C). This difference indicates that magnetic transformation occurs only in the electromagnetic soft iron at around Tc, while magnetic and phase transformations, from ferrite to austenite, occur simultaneously in the medium-carbon steel. The differences in the temperature-dependent coercive force for electromagnetic soft iron, and for the low and medium-carbon steels were observed in detail.& para;& para;The proposed method provided exact BH curves at high temperature, which were reflected by the complex and detailed magnetic behavior.