The influence of recrystallization on magnetic barkhausen noise in low carbon automotive sheet steels

Magnetic Barkhausen Noise (MBN) serves as a sensitive indicator of magnetic domain dynamics, which reflects the difference in mechanical properties of metal materials. Therefore, it has been widely used in non-destructive tests such as evaluating the residual stress and hardness of metal products. This study explores the microstructural characteristics of a low-carbon sheet steel subjected to various annealing temperatures, aiming to establish a correlation between its microstructure, mechanical properties and MBN parameters. The results showed that for the specimen annealed at 850 degrees C, the volume fraction of recrystallized grains characterized by Electron Backscatter Diffraction (EBSD) was higher than that of the specimen annealed at 750 degrees C. This was accompanied by a weaker MBN signal, indicating reduced strength and improved elongation. Furthermore, pseudo-in-situ Magnetic Force Microscopy (MFM) revealed that in the polycrystalline ferrite microstructure, recrystallized grains tend to form single domain configuration, whereas substructure grains exhibit multiple domains. The motions of magnetic domain wall in recrystallized grains becomes more prominent under varying magnetic fields, resulting in weaker MBN signals. Given the robust correlation between recrystallization, mechanical properties and MBN parameters, the study provides solid empirical support for using MBN technique to enable non-destructive testing of mechanical properties in low carbon steel sheets.