## 3 Results and Discussion
### Relationship between Microstructure and Mechanical Property  
From the investigation of the microstructure inhomogeneity, the content of ferrite at the core area is the lowest. However, it is obvious that whether the test was conducted  
Figure 8: ODF and IPF maps at typical locations on RD-ND plane by EBSD statistical analysis: (**a,d**) top surface; (**b,e**) core location; (**c,f**) bottom surface; (**a–c**) ODF maps; (**d–f**) IPF maps. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Texture** & **[223]** & **[113]** & **[112]** & **[001]** & **[110]** & **[332]** \\
**Percentage\(\backslash\)Type** & **\textless{}110\(>\)** & **\textless{}110\(>\)** & **\textless{}110\(>\)** & **\textless{}110\(>\)** & **\textless{}110\(>\)** & **\textless{}113\(>\)** \\ \hline Top surface & 14.3\(\%\) & 21.4\(\%\) & 19.9\(\%\) & 8.85\(\%\) & 8.46\(\%\) & 22.2\(\%\) \\ Core position & 23.2\(\%\) & 20.9\(\%\) & 22.2\(\%\) & 8.48\(\%\) & 3.9\(\%\) & 30.8\(\%\) \\ Bottom surface & 25.9\(\%\) & 25.4\(\%\) & 28.6\(\%\) & 9.16\(\%\) & 4.15\(\%\) & 22.6\(\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Types and contents of textures on the RD-ND plane by EBSD. Figure 7: The macrotextures of the ODF map on the RD-ND plane: (**a**) texture distribution on RD-ND plane; (**b**) common texture distribution of \(\varphi\)2 = 45\({}^{\circ}\) cubic crystal system. along the RD or along the TD, the elongation values of the core are always higher than that of both surfaces while the content of ferrite at the top surface is more than that of ferrite at the bottom surface (Figure 9). The result means that the content of ferrite is not the main factor affecting the elongation of the steel, whereas the content of martensite is one of the main factors affecting elongation of the steel. The variation of the amounts of martensite zone with high KAM values (Figure 6k) is highly consistent with the variation of elongation at typical locations (Figure 9). In addition, the results of tensile tests at typical locations (Figure 9, where the stress-strain curves of \"core location-1\" and \"core location-2\" are representatives of mechanical behavior of the core area) show that the tensile strength of the specimens along the RD and the TD exhibit obvious anisotropic features, which are about 1500 MPa and 1600 MPa, respectively, whereas the elongation in the RD direction is greater than that in the TD direction (Figure 9). The quantitative results of the strength and elongation values for both the rolling direction and the transverse direction are listed in Table 4. Based on the data in Tables 2 and 4, it is found that grain size ratio is closely related to variation of the mechanical properties at three positions, smaller grain size ratios, higher elongation, higher grain ratios, and lower elongation. The results mean that the higher content of martensite improves the elongation of the steel. Therefore, it is confirmed that the deformation degree of prior austenite grains during hot rolling and the martensite content after quenching dominate the mechanical properties. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Positions** & \begin{tabular}{c} **Yield** \\ **Strength/MPa** \\ \end{tabular} & \
\begin{tabular}{c} **Tensile** \\ **Strength/MPa** \\ \end{tabular} &
\begin{tabular}{c} **Elongation/\%** \\ \end{tabular} \\ \hline \multirow{3}{*}{RD} & Top surface & 1220 & 1467 & 6.6 \\  & Core location-1 & 1133 & 1487 & 8.6 \\  & Core location-2 & 1136 & 1490 & 8.2 \\  & Bottom surface & 1189 & 1492 & 7.6 \\ \hline \multirow{3}{*}{TD} & Top surface & 1315 & 1604 & 5.2 \\  & Core location-1 & 1259 & 1621 & 6.2 \\ \cline{1-1}  & Core location-2 & 1203 & 1578 & 6.6 \\ \cline{1-1}  & Bottom surface & 1328 & 1606 & 6.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mean values of mechanical properties of NM450 TP steel along RD and TD. Figure 9: Stress-strain curves at typical positions by tensile test: (**a**) RD; (**b**) TD.