Magneto-mechanical properties evolution of Fe–C alloy during precipitation process

Evolution of magneto-mechanical properties of 160 ppm Fe–C alloy due to ε carbides precipitation during isothermal annealing at 473 K (up to t=50×103 s) was studied by means of classical Barkhausen noise (HBN) and mechanical Barkhausen noise (MBN) effects. The MBN was measured for the torsion mode of load with a torque motor. Also the B(H) hysteresis loop and the coercive field Hc were evaluated using a low-frequency magnetisation set. Magnetic hysteresis losses ΔW1 were compared with the integral ΔW2 of HBN intensity over one period of magnetisation and the integral ΔW3 of MBN intensity over one period of the mechanical load. The internal stress distribution function and the resulting mean level of internal stress parameter σi were evaluated from the MBN ‘first load’ data. It was revealed that a correlated increase of ΔW1 and ΔW2 parameters exists. However, the relative increase of ΔW3 is much lower than the relative increase of ΔW1. The relationship between Hc and σi was found to be parabolic. This dependence explained by Néel’s model of the impact of the residual stress level on Hc. The presence of precipitates of type ε was confirmed by scanning electron microscopy.