Magnetic behavior of AISI 304 steel in uniaxial tensile tests

During the magnetization process of a ferromagnetic material, the magnetic domain walls are forced to move due to the magnetic field influence. The domain walls must overcome the stress produced by the pinning sites (grain boundary, dislocations, inclusions, etc.), producing discrete jumps in the magnetization. These jumps can be detected with a sensor coil located on the surface sample, transforming them in voltage pulses known as Magnetic Barkhausen Noise (MBN). This work is the follow-up of the study on the uniaxial tensile test up to breakage, on AISI 304 steel (non-magnetic) samples. As a consequence of the strain a new ferromagnetic phase appears which produces MBN. From the signals obtained during the measurements, a digital filter was designed and applied in order to eliminate any spurious signal and to identify the MBN. For this purpose a Butterworth digital filter was used with a (2-200) kHz bandwidth This filter was selected because it presents a practically constant response up to the cutoff frequency, giving a flat response over the entire passband. For each load value, the MBN signals were analyzed separately concerning the stages of increase and decrease of the magnetic field excitation. In order to characterize each stage, various statistical parameters were evaluated as a function of the applied strain. Finally, the time evolution of the signals and their root mean square function (RMS) were calculated for each stage of the magnetization, calculating the cross correlation function.