The Effect of Heat Treatment on Magnetic Properties of Fe78Si9B13 Amorphous Ribbons

Residual stresses resulting from rapid quenching of molten metal in melt spinning process can be removed by structural relaxation of samples at temperatures lower than the crystallization temperature in order to improve the magnetic properties. In this research, amorphous Fe78Si9B13 ribbons (Metglas 2605S2 used in transformer cores) with the thickness of 26 µm were prepared by chill block melt spinning. DTA measurements on the ribbons heated with the rate of 20 K/min showed that the starting crystallization temperature is 535 °C. The ribbons were then heat treated in a protective gas for 15 to 60 minutes at temperatures in the range of 300-560 °C. XRD results revealed an amorphous structure for all the heat treated samples except for the samples annealed at 500 and 560 °C in which the structure were consisted of three crystalline phases of α-Fe, Fe2B and Fe3B. The measurement of magnetic properties by Hysteresisgraph indicated that the saturation induction increases by an increase in the annealing time and/or annealing temperature. The best combination of magnetic properties was obtained after annealing at 400 °C for 15 minutes.