Evaluation of Plastic Deformation in Steels with Magnetic and Acoustic Techniques

Abstract

Barkhausen Magnetic Noise (MBN) and Magnetic Acoustic Emission (MAE) are phenomena that occur in ferromagnetic materials which undergo changes in their magnetization. These phenomena are very sensitive to changes on microstructure and residual stresses. The MBN and MAE can be applied as monitoring techniques to detect plastic deformation in materials subjected to thermomechanical processes, such as machining and manufacturing processes. In this work, the plastic deformation in samples subjected to uniaxial tensile tests is investigated through MBN and MAE. Twelve stainless steel test pieces of two different materials (AISI 430 and AISI 441A), were tested. As a first step, in order to obtain their mechanical properties, two test pieces of each material cut in different directions with respect to the rolling direction, were tested up to rupture. The others were deformed in four stages on plastic deformation. After each stage, MBN and MAE measurements were made, in order to obtain a correlation with the strain and the magnetic situation of the materials. We present here the microstructural analyses, the study of MBN and MAE signals, correlating them with the state of deformation of the specimens.

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“…As the plastic deformation increases, the dislocation density increases with an increase in the interaction between the MDW and the dislocations. The interaction between the observed, they are clearly seen in the region of the "knee" of each hysteresis cycle, where there is a separation that increases with deformation [17]. This is very important for MAE measurements, since these are the most active regions.…”

“…This fact is explained in the following way: As the plastic deformation increases, the dislocation density increases together with an increase in dislocations interaction with MDW. The interaction between the walls of the domains and the dislocations seems to be stronger for MDW of at 180°, than for MDW at 90° [13][14][15][16][17][18][19].…”