Stacks of steel plates having different values of magnetic hardness and separated with nonferromagnetic gaps are investigated. The coercive force and the residual magnetic induction of a stack measured in a closed magnetic circuit depend on the layout of the plates in the stack and on the thickness of nonmagnetic gaps between them.In the practical use of ferromagnetic materials, separate plates of the magnetic circuit are sometimes insulated from each other by special coatings and sometimes multilayered articles containing inserts with different physical, including magnetic, properties (surface-hardened layers and welded joints) are subject to nondestructive testing. Furthermore, stratification processes can develop in bimetallic materials and affect their magnetic properties. Since the magnetization-reversal process in such items has some specific features [1], these should be taken into account during operation of magnetic circuits with laminated cores and development of methods for nondestructive testing of multilayered and multicomponent articles.This investigation is devoted to the magnetization-reversal processes in a closed magnetic circuit containing three-layer articles with different magnetic properties and structural states. Articles made of tempered and annealed grade-45 steel in the form of plates finished to dimensions of 3 × 10 × 100 mm have been investigated.It was shown in [2-6] that the coercive force of a multilayered (and, in particular, a two-layer) article is not a physical constant generally used to characterize materials. It is actually a value of a demagnetizing current that ensures mutual compensation of magnetic fluxes in the layers. The value of such a coercive force depends not only on the coercive forces and the shape of the hysteresis loops of the constituent layers but also on the loops' geometry and on the external and internal demagnetization factors.Magnetic characteristics of four different stacks of grade-45 steel plates were investigated in different structural states (see the table). Stack 1 comprised three annealed plates with a coercive force of H c = 0.31 kA/m. Stack 2 consisted of three tempered plates with a coercive force of H c = 2.07 kA/m. Each of stacks 3 and 4 contained two identical magnetically hard h plates and one magnetically soft s plate. The coercive force of the magnetically hard component in stack 3 was about 7 times greater than that of the magnetically soft component, while in stack 4 the increase was only twofold. The layout of the plates differed in stacks 3 and 4 by the
MAGNETIC METHODS
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