Mechanism of magnetic domain refinement on grain-oriented silicon steel by laser irradiation

The residual stress distributions near the laser-irradiated line in a crystal grain of an electrical steel sheet were measured by the X-ray stress measurement method for a single crystal, in order to clarify the mechanism of the magnetic domain refinement which can be applied to reduce the core losses. A specimen containing only one grain was cut from a grain-oriented silicon steel, and was irradiated with a laser. The distributions of the residual stresses and those of the half value width (HVW) of the diffraction profile, which indicates the plastic strain level near the laser-irradiated line, were measured before and after the stress-relief annealing, and their magnetic domain structures were observed. Before annealing, the HVW was increased near the laser-irradiated line, since the local plastic deformation was induced by the peening effect of the laser irradiation and the process of melting, cooling, and contraction after the laser irradiation. Therefore, the tensile residual stresses were induced near the laser-irradiated line. Next, the magnetic domains were refined more than they were before the laser irradiation. After annealing, the HVW was constant at the initial value, and the residual stresses were relieved. The magnetic domain then returned to its original width. Therefore, it was confirmed that the magnetic domain was refined due to the residual stress induced by the laser irradiation.