The effect of plastic deformation an magnetic flux leakage signals in steel

The effect of plastic deformation in steel on magnetic flux leakage (MFL) s ignals was investigated by measuring the MFL signals from similar, electroc hemically milled defects on samples with varying degrees of plastic strain and for a range of magnetic flux densities. The results indicated that the MFL signals are sensitive to plastic deformation, which can alter these sig nals more than 50%, depending on the magnetisation in the sample. The MFL s ignals were initially found to decrease sharply with increasing plastic str ain and finally tended to saturate at higher plastic deformations. The obse rved dependence of MFL signals on plastic strain has been explained by corr elating it with the changes in the easy axis of magnetisation, induced by p lastic deformation. Magnetic Barkhausen noise measurements have been used t o study the changes in the direction of the easy axis of magnetisation and magnitude of anisotropy in plastically deformed samples. These directional magnetic anisotropies have been related to the observed dependence of MFL o n plastic strain.