Ferromagnetic Materials

Abstract

Ferromagnetic properties of materials exert a profound influence upon EC NDE. Successful interpretation of EC measurements on many steels or other types of ferromagnetic conductor requires an understanding of the magnetization (and demagnetization)  processes that occur in ferromagnetic materials. This chapter builds upon the role of electric current as the fundamental source of the magnetic field to explain the phenomenon of magnetization, to describe hysteresis, and to show the nonlinear character of permeability. Energy arguments are invoked to explain the existence of ferromagnetic domains and domain processes are described. Methods of demagnetizing test-pieces to regularize them for EC inspection are suggested. Description of the role of low-conductivity ferromagnetic ceramics (ferrite cores) in EC coil construction is described in Chap. 6, Signals and Coils.