NDTnet 1998 Aug, Vol.3 No.8

Abstract

Basing on the concept of independent subsystems of 90° and 180° domain boundaries (DB) with different distributions of the critical magnetic reversal fields (H ) we succeeded in the explanation of the interactions and factors that result in the experimentally observed value of the coercivity (H_c) for the polycrystalline heterogeneous ferromagnetic steels in distinct structural states.

Although the coercivity is caused by only two interactions - magnetic and magnetoelastic one, they affect on the H_cr⁹⁰ and H_cr¹⁸⁰ differently: the contributions of internal leakage fields at nonmagnetic inclusions to the H_c⁹⁰ and H_c¹⁸⁰ are of the same order of magnitude, but it is not true for the internal stresses _i. Namely, only gradients of the _i (actually, their variations along the thickness of the DB) contribute to the H_cr¹⁸⁰ and there is an additional contribution of the stresses by themselves to the H_cr⁹⁰. As a result, the inequality H_c⁹⁰ >> H_c¹⁸⁰ holds in most typical cases, and the resulting coercivity is caused mainly by displacements of the 180° DBs in terms of the Weiss anisotropy law, wich considers a random distribution of orientations for domain magnetization vectors (as a consequence, the magnetic reversal of the regions with the same HCr values takes place at different fields).

The mechanism of the influence of external elastic stresses ₀ on the coercivity in ferromagnetic steels is explained in terms of the concept being under development, and it considers the following factors: variation of the mean value of the angle included between domain magnetization vectors and the coo direction due to the 90° DB displacements (they start at |₀| > _i^-where _i- - mean internal stresses); variations of gradients for internal stresses of the 2nd kind; compensation of internal stresses by external stresses in those regions where their signs are mutually opposite, wich leads to the appearance of the minima of H_c⁹⁰ (₀) and H_c¹⁸⁰ (₀)relationships.The division into internal stresses of the Ist, 2nd and 3d kind obtains its physical sense within the scope of the present concept.The conditions are determined for the applicability of the coercivity to assess the internal and external elastic stresses in ferromagnetic products and constructions.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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