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The possibilities of certification of hardened surface layers by measurement of coercive force, eddy current inspection and analysis of the field dependence of differential magnetic permeability m d (H ) are considered. The advantages of analysis of the pattern of peaks on the m d (H ) dependence for estimating the state of surface-hardened steels subjected to subsequent force loading are shown.

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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

The mechanical, magnetic, and thermal properties of water-quenched (from 1150 ° C) alloys, such as ç 36 ä 10 í 3, ç 36 ä 10 ï5í 2, and ç 36 ä 5 í 2, which were strengthened by aging (at 650 ° C) and high-temperature deformation (1100-800 ° C) followed by aging, are studied. The decomposition of a supersaturated solid solution in the Invar alloys under study was shown to increase the strength properties and coercive force but to decrease the plasticity and saturation magnetization. In this case, the aging ambiguously affects thermal expansion coefficient α of the different alloys; the temperature range of invariance decreases. The plastic deformation of Invars was found to increase the ultimate strength, yield strength, and coercive force. The additional aging of deformed materials increases the strength and decreases the plastic properties; among the magnetic parameters, the saturation magnetization exhibits the most adequate correlation with the mechanical properties. The thermal properties (the α coefficient and invariance range) resulting from the complex heat treatment differ slightly from those resulting from the single aging.