The magnetic properties of plastically deformed steels

Abstract

The magnetic properties of plastically deformed steels. The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source• a link is made to the metadata record in Durham E-Theses• the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. The copyright of this thesis rests with the author.No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. The changes in the magnetic properties after tensile deformation are similar to those due to elastic compressive stress, with an additional increase in the coercivity. For the initial magnetisation curve initial permeability (J-Li) and maximum relative permeability both decrease, while the field at which the latter occurs (Hm) The Magnetic Properties of Plastically Deformed Steelsincreases. The hysteresis curve shears over reducing the maximum differential permeability and the remanence and also increasing the coercivity. These results and the change in the shape of the hysteresis curve, most noticeable in the low carbon steels, are explained in terms of the reduction in easy domain wall movement due to the dislocation tangles, as observed under the electron microscope, and to the magnetostrictive effect of the compressive residual stress.Inter-relationships are found between coercivity and both J-Li and Hm. The coercivity io also found to vary linearly with both Vickers Hardness and Yield Stress. The Kneppo formula for the initial magnetisation curve is found to hold better for the higher carbon content steels with the fit deteriorating with increasing plastic deformation.

Prediction of the Mechanical Properties of P91 Steel by Means of Magneto-acoustic Emission and Acoustic Birefringence

“…When tensile stress is applied and exceeds the yield point, a rapid dislocation multiplication occurs [29]. The dislocations readily pile up and create dense dislocation tangles with a high degree of tensile deformation, leaving the bulk of the specimen in residual compression after unloading [29].…”

Hysteresis minor loop analysis of plastically deformed low-carbon steel

“…However, in general case of magnetic NDT control of plastically deformed steels the directional dependence of the magnetic properties should be taken into account. It is known that magnetic behavior in the transversal direction to the previous uniaxial elongation is quite different: the permeability has usual one-peak form [17] and the classical magnetic parameters show similar behavior but smaller sensitivity to strain than in the investigated axial direction [28]. Moreover, magnetically and mechanically harder steels with greater number of different inclusions in ferritic matrix are supposed to be a more difficult problem for magnetic NDT in comparison with the presented low-carbon steel case.…”

The Role of Surface Topography on Deformation-Induced Magnetization under Inhomogeneous Elastic-Plastic Deformation

“…For example, a high dislocation density increases the coercive force and decreases remanence and permeability. Highly plasticized material regions, hence, become magnetically harder than other material regions [ 73 , 74 ]. Due to these position-dependent permeability changes, magnetic stray fields may arise, wherein the absolute values depend greatly on internal magnetic fields.…”