Magnetic measurement to evaluate material properties of ferromagnetic structural steels with planar coils

Nondestructive measurement experiments were carried out with a planar coil to evaluate changes of material properties of ferromagnetic structural stee ls. Examined steers were of A533B that is a low-alloy steel and of SUS410 t hat is a martensitic stainless steel The planer coil has two windings; one is of primary for excitation and the other secondary for induction of outpu t voltage, The coil was placed on a test plate with a magnetic yoke for app lication of a bias de magnetic field, and excited with a constant current o f 25 Hz. Then the output voltages were measured while slowly changing the b ias field by excitation of the magnetic yoke with a triangular-wave form cu rrent of 0.005 Hz. Changes of output voltages with different test plates we re correlated with their mechanical and magnetic properties. The correlatio n is so good that this measuring method could be applied to nondestructive evaluation of material degradation in ferromagnetic structural steels.