Detection of Temper Embrittlement in Steel by Magnetoacoustic Emssion Technique

A bulk ferromagnet possesses two types of domain walls: 180° and non-180° [1]. In the case of iron-like ferromagnets, the latter type of walls are 90° domain walls. As a result of the magnetoelastic interaction, unit cells of a ferromagnet deform slightly in a way that is unique to particular types of domains [2]. Such a spontaneous deformation, called magnetostriction, causes local lattice strains at domain walls with the strain fields being particularly strong for 90° domain walls [3]. The motion of the 90° domain walls is followed by a redistribution of local lattice strain fields. Elastic energy is being released by this process and propagates through material as acoustic waves. Acoustic emission (AE) generated due to magnetic domain wall motion is thus defined as magnetoacoustic emission (MAE)