## 4 Applications
### Applications in the Steel Industry
#### 4.2.1 Inline Strip Steel Testing
Based on the 3 MA technique, an online testing system for the continuous determination of tensile strength (Rm), yield strength (Rp0.2), and other mechanical-technological characteristics in a broad range of steel grades was developed. The 3 MA probe head is integrated into a movable, rotatable holder (see Figure 9). The orientation between the main magnetic field and the rolling direction of the strip can be adjusted to 0\({}^{\circ}\), 45\({}^{\circ}\)and 90\({}^{\circ}\), which offers the possibility of determining the anisotropy parameters \(\mathrm{r_{m}}\) and \(\mathrm{\Delta r}\) from the 3 MA measurements. Again, the probe holder is mounted onto a hydraulically adjustable table carrier, which was equipped with distance rollers. A fast lowering of the entire construction in the case of an escape warning is necessary to avoid damaging the probe due to weld seams or zinc deposits on the strip. The external electronic equipment that is integrated into the measuring cabin controls the measuring procedure. The electronic equipment mainly consists of the 3 MA measuring module, the electro-pneumatic device control, interfaces to supporting signals, like weld seam recognition, meter pulse, or strip velocity signals, and interfaces to the plant process control (PCS) and data management (DMS) systems of the strip steel production line. For calibration, about 11,000 strips from 12 different steel grades were used. In contrast to the first IP+EMAT equipment described above, here it was not necessary to develop individual calibrations for each steel grade. Rather, it was found that the 12 steel grades could be combined into only four calibration classes, which are shown in Table 6.  
Figure 8: Inline measurement of vertical anisotropy \(\mathrm{r_{m}}\) and planar anisotropy \(\mathrm{\Delta r}\) in a coil of 2300 m in length. Figure 9: Rotatable 3 MA probe head holder and table carrier of the 3 MA inline strip testing system. Besides standard steel qualities (normal steel and construction steel), interstitial-free (IF) steel, and high strength material were investigated. The 3 MA data that were determined at the beginning and at the end of the strip were associated to the destructively determined data of Rm and Rp0.2 data in order to determine the calibration functions. Table 6 also shows the results of this calibration in terms of the RMSE of the correlation between the 3 MA data and destructive data. In order to verify the calibration, i.e., to check the quality of the developed calibration functions and to evaluate the measurement accuracy of this 3 MA application, a series of comparing measurements was carried out with the calibrated 3 MA system. The nondestructively (nd) determined values of Rm and Rp0.2 were compared with the values that were measured from destructive (d) tensile tests at over 2700 strips. The diagrams of Figure 10 show the results of this comparison. The data from all four steel grade classes are combined in these diagrams. In order to evaluate the deviation between nd data and d data, the RMSE values for the four steel grade classes are shown in Table 7.  
According to the rules of error propagation, the measuring uncertainties of both methods (nd and d) will contribute to the RMSE, i.e.,  
\[RMSE=\sqrt{{u_{nd}}^{2}+{u_{d}}^{2}} \tag{2}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Steel Grade Class** & **RMSE of Rm [MPa]** & **RMSE of Rp0.2 [MPa]** & **No. of Strips** \\ \hline IF, conventional & 5.4 & 8.2 & 2667 \\ IF, high strength & 11.3 & 12.3 & 7764 \\ Bakhehardening & 5.8 & 8.8 & 1294 \\ Structural & 7.9 & 10.1 & 164 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Steel grade classes and calibration results. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Steel Grade Class** & **RMSE of Rm [MPa]** & **RMSE of Rp0.2 [MPa]** & **No. of Strips** \\ \hline IF, conventional & 5.3 & 7.4 & 1985 \\ IF, high strength & 6.8 & 9.3 & 68 \\ Bakhehardening & 11.2 & 15.6 & 55 \\ Structural & 7.5 & 12.4 & 34 \\ \hline \hline \end{tabular}
\end{table}