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On the mechanism of nondestructive evaluation of cementite content in steels using a combination of magnetic Barkhausen noise and magnetic force microscopy techniques

: Batista, Leonardo; Rabe, Ute; Altpeter, Iris; Hirsekorn, Sigrun; Dobmann, Gerd

Postprint urn:nbn:de:0011-n-3035033 (1.2 MByte PDF)
MD5 Fingerprint: 578020bd91b87b2b8d5f63754c285011
Created on: 19.8.2014

Journal of magnetism and magnetic materials 354 (2014), pp.248-256
ISSN: 0304-8853
Journal Article, Electronic Publication
Fraunhofer IZFP ()
magnetic force microscopy (MFM); electron backscatter diffraction (EBSD); steel; magnetic domains; Barkhausen noise; non-destructive testing

The influence of the carbon content in form of globular cementite precipitates in unalloyed steels was macroscopically characterized by means of magnetic hysteresis loop and Barkhausen noise techniques. The choice of the frequency of the applied field has a strong influence on the Barkhausen noise profiles. At sufficiently high frequency (0.5 Hz) there are two peaks, one at lower field, the amplitude of which corresponds to the amount of ferrite and one at higher field, the amplitude of which corresponds to the amount of the cementite phase, respectively. Magnetic force microscopy and electron backscattered diffraction techniques were used to determine the magnetic and crystallographic microstructures of the steels. Cementite has its own domain structure and stray fields which influence the magnetization process of the steel by its own magnetic contribution. When an external magnetic field is applied, the magnetization process in ferrite occurs mainly at lower fields through the 180° and 90° domain walls. A higher field is required for the observation of 180° domain wall movements in cementite.