Magnetic Barkhausen Noise and Magneto Acoustic Emission in Stainless Steel Plates

When a slowly variable magnetic field (∼ Hz) is applied through a yoke on a ferromagnetic material, discontinuous changes on the magnetic flow density are produced. This phenomenon, called Magnetic Barkhausen Noise (MBN), obeys the movement of magnetic domain walls and its frequency range is about [10-100] kHz. It involves sudden magnetization changes and localized variations of mechanical stresses which originate elastic waves known as Magneto Acoustic Emission (MAE) on the frequency range of 20 kHz up to 1 MHz. Both, MBN and MAE depend on the material microstructural characteristics and they may be considered as non-destructive evaluation techniques. This work is based on MBN and MAE tests carried out on 5 groups of different stainless steel specimens (AISI 409, AISI 430, AISI 439, AISI 441A and AISI 444), for two applied magnetic fields, parallel and perpendicular to the rolling direction.