## 3 Results and Discussion
### MBN Measurements
When the altered magnetizing field is strong enough, all regions can be magnetized in the direction of this field (magnetizing field highlighted by the yellow arrows); see Figure 13b,c. As soon as the magnetizing field falls below the critical threshold, the full DW alignment can be found only in the direction of the remnant magnetization; see Figure 13d. On the other hand, the effect of magnetic coupling prevails when the magnetic field is in the opposite direction to the remnant magnetization. The blue region does not contribute to the magnetization process in such case and MBN is lower in the magnetized state; see Figure 13e. \[v_{p}=\frac{dM}{dt}=(H-H_{c})^{q} \tag{1}\]4 _FWHM_ after demagnetization versus _FWHM_ before demagnetization: (**a**) _FWHM_ in the RD—side A and (**b**) _FWHM_ in the TD—side A.  
\[v_{p}=\frac{dM}{dt}=(H-H_{c})^{q} \tag{1}\]5 Magnetization process as a function of magnetizing field strength as well as remnant magnetization orientation: (**a**) the direction of remnant magnetization in demagnetized state, (**b**) magnetization in the direction of remnant magnetization at high voltage, (**c**) magnetization in the direction of remnant magnetization at low voltage, (**d**) magnetization in the opposite direction with respect of remnant magnetization at high voltage, (**e**) magnetization in the opposite direction with respect of remnant magnetization at low voltage. Therefore, preliminary demagnetization in much stronger magnetic fields (vanishing in strength) should be carried out before MBN measurements. On the one hand, the used sensor is capable of producing a stronger magnetic field altering in time [41], which might suppress the asymmetry in consecutive MBN bursts. However, the application of such magnetizing conditions can also result in a weaker sensitivity of MBN measurements to microstructure alterations and/or stress state, as reported in, e.g., [42; 43; 44]. Finally, a brief explanation of the heterogeneity in MBN along the sheet width should be noted. MBN fluctuates in the range from 540 to 1440 mV. Such significant non-homogeneity in MBN can be addressed in different ways. The first one is based on the residual stress state, the second one is based on the microstructure alterations expressed in a variety of related aspects, and finally, the superimposing consideration of both might be considered as well. It was observed that the bulk residual stress is close to zero. The compressive stresses of magnitude of about \(-150\) MPa can be found for the positions of MBN 540 mV for the RD. This stress is released at an early 10 \(\upmu\)m below the free surface and reaches the bulk value. The magnitude of these compressive stresses drops down along with the increasing MBN and also releases early. The evolution of residual stresses in the TD is very similar; only the compressive stresses are about 100 MPa higher. Despite the low magnetostriction of steel, a certain contribution of decreasing stresses with respect to the increasing MBN can be considered. However, it is considered that the main role in increasing the level of MBN should be related to the altered microstructure. Two basic aspects are detected. The first one is linked to the decreasing dislocation opposition in the near-surface region along with the increasing MBN as a result of surface decarbartian. The HV0.1 15 \(\upmu\)m below the surface was measured to be 304 \(\pm\) 8 for MBN 540 mV in contrast to the bulk HV0.1 496 \(\pm\) 6. The surface softening progressively vanishes towards the depth, and the affected depth is about 200 \(\upmu\)m. However, this softening is more developed (expressed in terms of HV0.1 and its depth extent), along with the increasing MBN, and HV0.1 for MBN 1440 mV is 249 \(\pm\) 12 (the affected depth is approximately 100 \(\upmu\)m deeper in contrast to the position in which MBN is 540 mV). Finally, it should also be mentioned that MBN is also driven by the presence of very fine carbides produced during rapid cooling [3; 4; 5].