# Grain Refinement and Improved Mechanical Properties of EUROFER97 by Thermo-Mechanical Treatments
## 3 Results and Discussion  
### Work-Hardening Behavior of EUROFER97 Steel  
The effect of cold rolling on the EUROFER97 microstructure is shown in the SEM images of Figure 2. Figure 2a shows the microstructure of EUROFER97 steel after the standard treatment consisting of tempered martensite with carbides decorating the prior austenitic grains (PAGs) and former lath packet boundaries. A detailed analysis of carbide types, chemical composition, morphology and spatial distribution confirmed results already reported in the literature (e.g., [57; 58]). Coarse M\({}_{23}\)C\({}_{6}\) (M = Cr, W) carbides decorate the PAG and the boundaries of martensite lath packets while the MX (M = Ta, V) carbo-nitrides are finely dispersed inside the lath structure. The micrographs in Figure 2b-f display the microstructures after cold rolling with increasing CR ratio. As expected, the original grains tend to progressively become flat and elongated along the rolling direction and this characteristic becomes more evident with larger CR ratios. As indicated by red arrows in (b), inside some original grains, a population of new grains with size below \(\sim\)1 \(\upmu\)m forms. For the highest degree of deformation (CR ratio of 80%) the elongated grains were fragmented into new equiaxed grains with mean size of \(\sim\)400 nm. Figure 1: Schematic drawing of a typical probe used in tensile tests (dimensions are expressed in millimeters). Figure 3 shows the XRD patterns of samples prepared by means of the standard treatment and after cold rolling with increasing CR ratios. In each pattern the relative intensities of peaks (see Table 2) provide information about possible textures, i.e., preferred orientations of the grains. The texture can be evaluated by comparing the relative intensities measured in the experiments with those reported in the JCPDS database-file 6-696 [59]. Figure 2: EUROFER97 steel. SEM micrographs of the material in standard condition (**a**) and after cold rolling with increasing CR ratio: 20% (**b**), 40% (**c**), 50% (**d**), 60% (**e**) and 80% (**f**). corresponding to Fe with randomly oriented grains. If the examined material has a texture the intensities diverge from such reference values: the greater the difference, the stronger the texture. The samples prepared by means of the standard treatment exhibit a nearly random texture with the presence of a weak [110] component. Such texture then evolves towards a cubic [100] one with a secondary [211] component observed for the greatest CR ratio (80%). Another effect of increasing values of CR ratio is the progressive broadening of XRD peak profiles. For example, Figure 4 shows the evolution of the {110} peak; the peak intensities are normalized to make easier the comparison. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Peaks** & **110** & **200** & **211** & **220** & **310** & **222** \\ \hline JCPDS database-file 6-696 & 100 & 20 & 30 & 10 & 12 & 6 \\ \hline Standard & 100 & 11 & 20 & 8 & 6 & - \\ \hline CR 20\% & 100 & 24 & 27 & 6 & 9 & 5 \\ \hline CR 40\% & 100 & 15 & 38 & 6 & 7 & 4 \\ \hline CR 50\% & 100 & 7 & 12 & 5 & 4 & - \\ \hline CR 60\% & 100 & 20 & 30 & 1 & 1 & 1 \\ \hline CR 80\% & 100 & 52 & 63 & - & 1 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Relative intensities of XRD peaks of EUROFER97 steel prepared according to the standard treatment and after cold rolling with increasing CR ratio. The values have been determined from patterns in Figure 3. Data from the file 6-696 of JCPDS database [59] referring to Fe with randomly oriented grains are reported for comparison. Figure 3: XRD patterns of standard EUROFER97 steel and after cold rolling with increasing CR ratio. From the analysis of XRD peak profiles the dislocation density were calculated by means of Equation (2) and the results are reported in Figure 5. Some TEM observations have been published in a previous work [20] confirming the XRD data.