Sharp Increase of Hysteresis Area Due to Small Plastic Deformation Studied With Magnetic Barkhausen Noise

Three steels with similar microstructure but with very different mechanical properties were examined with nondestructive technique magnetic Barkhausen noise (MBN). All these steels were submitted to a very small plastic deformation (tensile test), varying between 0.5% and 4% of deformation. It was found that 180° domain wall movement becomes difficult, even after very small deformation of 0.5%. This is caused by grain fragmentation due to plastic deformation and by an increase of the dislocation density, with formation of dislocation tangles and dislocation cells. The change of the MBN envelope shape suggests that the magnetostrictive process becomes more important after plastic deformation, and this probably is related to the stress field around dislocations.