Microstructure and magnetic properties of Fe-Cr-Co-V alloys

The relationship between the microstructure and magnetic properties of heat treated Fe–23 wt%Cr–15 wt% Co–5 wt%V has been studied by transmission electron microscopy and Lorentz microscopy. Three different heat treatments were adopted for the present investigations, viz., (1) isothermal aging, (2) thermomagnetic treatment (TMT) + step-aging, (3) continuous cooling. It has been found that the magnetic properties of the alloy are very sensitive to the temperature of the TMT. Step-aging gave the best magnetic properties, producing an elongated ferromagnetic phase, 300 Å in diameter and 1200 Å in length. Lorentz microscopy revealed domain walls and these lie within the Cr-rich phase and pinned by the Fe-rich phase in the isothermally aged alloy at 650 °C. Magnetic domains of optimally step-aged alloys, 0.5 μm in width, are elongated along the direction of the applied magnetic field. The results suggest that the magnetic anistropy is introduced parallel to the direction of the applied magnetic field during TMT and step-aging treatments.