Characterization of cementite in steel and white cast iron by micromagnetic nondestructive methods

The influence of different cementite contents and cementite modifications on micromagnetic measuring quantities of steels with ferritic-perlitic, martensitic annealed and martensitic soft annealed microstructure states and white cast iron are analyzed. For this, micromagnetic measuring quantities derived from the magnetic Barkhausen noise are used. By heating up to temperature values above the Curie temperature of cementite, characteristic changes of the measuring quantities are shown. Cementite produces actively its own magnetic Barkhausen noise, whereas it also influences the magnetic Barkhausen noise of the iron matrix as a foreign body and by its stress fields of the second kind. Both influences act in a different way as well in steel as in white cast iron. In steel, the stress induced effect is the dominating one; in white cast iron, the active contribution to Barkhausen noise dominates.