The Dominant Influence of Plastic Deformation Induced Residual Stress on the Barkhausen Effect Signal in Martensitic Steels

Abstract

The paper presents the results of investigation of the influence of plastic deformation on the magnetic properties of martensitic steel (P91 grade). The properties of the hysteresis loops as well as of the Barkhausen effect (BE) signal are analysed for both tensile and compressive loading up to ε = 10% of plastic deformation. The choice of the steel and of the deformation range is unique, since for such combination one can expect high residual stresses (both compressive and tensile) in the material that does not exhibit saturation of the BE intensity as a function of elastic stress. The obtained relationships show that for the low level of deformation the dislocation density changes may play a dominant role, yet for higher deformation level the residual stress becomes a dominant factor. It leads to the strong decrease of the BE signal for tensile deformation and an increase for the case of compression. It agrees well with the assumption that the tensile plastic deformation results in the compressive stresses appearance in the soft (magnetically active) subregions of the material whereas for the compression one can expect a residual stress of a tensile nature in those areas. Both deformation modes result in the increase of coercivity of the samples, yet the increase observed for the tensile deformation is significantly higher since both the residual compressive stress and increase of dislocation density have a strong effect on the material coercivity.

On the application of magnetoelastic properties measurements for plastic level determination in martensitic steels

“…As it turned out the obtained dependence of the filtered MAE signal intensity on the deformation level is very similar, yet due the better resolution, one can observe that the changes due to the tensile deformation are in fact non monotonous there is a local maximum for ε = 1.6%. One could suspect that to be an erroneous result, yet analogous maximum was observed for the BN signal intensity [4]. Probably it is due to creation of a dislocation cell structure for that range of deformation.…”

Methodology and Experience in Applying a Non-Destructive Testing Method by Barkhausen Noise Analysis, for Example, in Ion-Treated Samples

“…It has been shown that they can be characterized by analysing the characteristics of the magnetic noise [1,2], caused by the dislocations in the microstructure in the examined ferromagnetic material. The information provided by these characteristics enables differentiated processing of the information used to evaluate the multiparameter analysis of the nitriding mode and other types of processing of each individual input parameter [3,4,5]. This is possible thanks to the property of ferromagnetic bodies discovered by Barkhausen, whose magnetization under the action of an external magnetic field is accompanied by numerous jumps in magnetization.…”