The influence of heat treatment conditions in an external magnetic field on the structure and magnetic properties of the Fe-25Cr-12Co alloy

This work presents an attempt to define the qualitative and quantitative changes in microstructural parameters of Fe-Cr-Co alloy microstructure depending on the parameters of heat isothermal high-temperature aging and magnetic treatments. Two alloys of nominally similar Cr and Co contents, but containing differing impurities, were tested for the determination of the influence of impurities on the values of B_r, H_c and (BH)_max. High-temperature aging was carried out by two methods: (i) an isothermal process and (ii) continuous cooling in an external magnetic field; values of their magnetic properties were compared. Changes in particle size of the ferromagnetic phase ₁ as well as its surface content, specific surface and structure anisotropy coefficient were defined for the material as function of the temperature of isothermal high-temperature aging. The results obtained enabled discussion of individual influence of microstructural parameters during magnetic hardening of Fe-Cr-Co type alloys. Results from TEM examinations show that microstructural parameters are sensitive functions of isothermal heat-magnetic treatment and in this process a very precise control of its parameters is required. On the grounds of investigations performed, magnetic aging with continuous cooling is found to be the most favourable treatment, since owing to the wider range of the admissible parameters of treatment it allows for higher tolerance as regards the technological parameters.