## 4 Applications
### Applications in the Steel Industry
#### 4.2.1 Inline Strip Steel Testing
Destructive tensile tests (Rp0.2) and strain tests (\(\mathbf{r}_{\text{m}}\) and \(\Delta\mathbf{r}\)) were used in order to determine the reference values for calibration. Figures 5 and 6 show the typical calibration results. These calibration plots show the nondestructively predicted values of Rp0.2 (from 3 MA and from EMAT) as a function of the destructively measured values (from ref.). It was apparent that the best correlations could be found if an individual calibration model for each steel grade is used, as shown in the examples of Figures 5 and 6. It was also observed that sheet thickness has a distinct effect on the measured IP signals. This is due to the material's  
Figure 4: First prototype system for continuous testing of strength (Rp0.2) and deep-drawing (\(\mathbf{r}_{\text{m}}\) and \(\Delta\mathbf{r}\)) parameters in strip steel based on a combination of the Incremental Permeability (IP) and the EMAT measuring technique: (**a**) Top view of the sensor, showing the IP sensor (IP) as well as the two EMAT sensors (EMAT_RD and EMAT_45\({}^{\circ}\)); and, (**b**) Complete table carrier with two stabilization rollers. Figure 5: Results of the calibration to yield strength Rp0.2 based on measuring parameters from IP measurements, combined with sheet thickness; nondestructively predicted values of yield strength (from IP) are shown as a function of destructively measured values (from ref. ): (**a**) for a steel grade IF_1 and (**b**) for a steel grade IF_2. microstructure gradient resulting from skin-path rolling. The electromagnetic fields that were used for IP measurements cannot completely penetrate the material thickness (skin depth). Therefore, the microstructure at the surface of the material affected by skin-path rolling will have a more or less pronounced effect on the IP signal, depending on the sheet thickness. For that reason, it makes sense to either use an individual calibration model for each sheet thickness or to integrate the sheet thickness as a parameter in the calibration functions. The latter variant was applied in the work that is described here. As shown in Figure 5, the correlation coefficients R\({}^{2}\) were quite high (0.7-0.8) and the root mean square errors RMSE were quite low (4-6 MPa). The calibrations for r\({}_{\text{m}}\) and \(\Delta\)r provided values for R\({}^{2}\) that were in the range between 0.6 and 0.8 and RMSEs between 0.04 and 0.06. Nevertheless, it has to be considered that the value ranges are quite low for these calibrations, which promotes small RMSE values. Based on the above calibrations, continuous inline measurements of Rp0.2, r\({}_{\text{m}}\), and \(\Delta\)r were made. Figures 7 and 8 show some of the results. In the measuring plot of Figure 7, it can be observed that the strip leaves the acceptance range (130-180 MPa) at position x = 2100 m. This is later confirmed by the destructive measurements. The results of the inline measurements of r\({}_{\text{m}}\) and \(\Delta\)r in the same coil are shown in Figure 8.  
Figure 6: Results of the calibration to deep-drawing parameters based on measuring parameters from electromagnetic acoustic transducer (EMAT) measurements; nondestructively predicted values (from EMAT) are shown as a function of destructively measured values (from ref. ): (**a**) for vertical anisotropy \(\text{r}_{\text{m}}\) and (**b**) for the planar anisotropy \(\Delta\)r.  
Figure 7: Inline measurement of yield strength Rp0.2 in a coil of 2300 m in length. Destructive measurements of Rp0.2 at the beginning and at the end of the strip are also shown as white squares with error bars. At a later point, the prototype that is described above was substituted by an inline measuring system based on the complete 3 MA technique, i.e., besides IP also BN, HA, and EC were implemented in the system. The use of EMAT sensors for measuring deep-drawing parameters was no longer necessary.