Magnetic ageing investigation of bulk low-carbon silicon steel

•Rapid magnetic ageing of claw pole rotor under real-time thermal operating conditions.•Magnetic ageing has no significant effect on the electrical conductivity.•The magnetic ageing effects are observed on magnetic losses and mechanical hardness.•The magnetic ageing is associated to precipitation of carbides.•Heterogeneous ageing kinetic due to thermal gradients in the manufacturing process. In this paper, the magnetic ageing of a bulk forged non-annealed magnetic core, used in claw pole synchronous machine, is investigated. The study is carried out by characterizing the material properties of two groups of samples subjected to a thermal ageing at 180 °C that corresponds to the maximum operating temperature of the claw pole rotor. The investigated characteristics are the electrical conductivity, the magnetic properties, the material microstructure and the Vickers hardness. They were characterized along with the ageing time. The results show that, during the thermal ageing, the hysteresis losses and the Vickers hardness have been affected by the magnetic ageing, whereas the electric conductivity and the normal B-H curve have not been modified. The microstructure analyses showed that carbides precipitates were the main cause behind the magnetic ageing. Moreover, the comparison between the results of two groups of samples revealed the possibility that the magnetic ageing of the material could have started during the manufacturing process of the magnetic core.