Quantitative Nondestructive Evaluation of Cementite in Steel and White Cast Iron by Ferromagnetic Parameters

The change in the microstructure state (lattice defects, especially dislocations, precipitations and thus the stress fields) with the addition of alloying elements plays an important role for the strength and the toughness of a material. In order to determine these microstructural parameters, up to now the electron microscopy and similar methods are used. X-ray methods are normally used to determine residual stresses

Quantitative nondestructive evaluation of cementite in steel and white cast iron by ferromagnetic parameters

By heating the two-phase-material above the Curie temperature of the corresponding cementite phase, cementite-specific changes in the Barkhausen noise curve such as the decrease in the Barkhausen noise maxima, the broadening of the Barkhausen noise curve delta M, changes in the coercive force could be observed. On the one hand, these changes in the magnetic parameters can be understood from the decomposition of the average residual volume stresses of the second kind in the ferrite matrix, on the other hand, they can also be understood from the lack of active noise contribution from the cementite phase. The parameters derived from the magnetic Barkhausen noise can be used to determine the cementite content, when the microstructure state is known. When the steel grade is known, the microstructure state can be detected from the pattern of the Barkhausen noise curve by means of simple pattern recognition. When the steel grade is unknown, the coercive force derived from the Barkhausen noise curve must be used as an additional parameter for characterization of the microstructure state