Nondestructive evaluation of cementite content in steel and white cast iron using inductive Barkhausen noise

A nondestructive testing method for the determination fo the cementite content in iron-carbon steel and white cast iron is presented. The method is based on micromagnetic measuring parameters derived from inductive Barkhausen noise measurements taken under room temperature and with temperautres above the Curie temperature. The influence of different cementite contents and cementite modification on the micromagnetic measuring quantities for steels with ferritic, pearlitic, martensitic annealed and martensitic soft annealed microstructure states and for white cast iron was determined. Cementite actively produces its own inductive Barkhausen noise and also influences the Barkhausen noise of the iron matrix both as a foreign body and by its stress fields of the second kind. Each influence has a different effect on steel and on white cast iron. It was shown that parameters derived from the Barkhausen noise can be used for determining the cementite content if the microstructure state is know n. Morcover, when the steel grad is known, the microstructure state can be detected from the pattern of the Barkhausen noise curve by means of simple pattern recognition.