 The annealing alters the material's crystal structure, aligning the grains and removing some impurities, especially carbon, which obstruct the free motion of the magnetic domain boundaries.Bending or mechanical shock after annealing may disrupt the material's grain alignment, leading to a drop in the permeability of the affected areas, which can be restored by repeating the hydrogen annealing step.Mu-metal is a soft magnetic alloy with exceptionally high magnetic permeability.