# Grain Refinement and Improved Mechanical Properties of EUROFER97 by Thermo-Mechanical Treatments
## 2 Materials and Methods  
The nominal chemical composition of EUROFER97 steel is reported in Table 1 [1]. A plate of EUROFER97 steel prepared according to the standard treatment was cut in five parts and each part was cold rolled with a different cold reduction (CR) ratio: 20, 40, 50, 60 and 80%. From each cold rolled sheet specimen was machined and then annealed at eight different temperatures from 400 \({}^{\circ}\)C to 750 \({}^{\circ}\)C (steps of 50 \({}^{\circ}\)C), for 1 h in an argon atmosphere. The heat treatment temperatures were chosen to operate in the ferritic field [41]. By combining cold rolling ratio and treatment temperature, 40 different sets of specimens were prepared. The microstructure of EUROFER97 samples was examined by high-resolution electron scanning microscopy (FE-SEM- Zeiss, Gemini Supra 25, Jena, Germany), light microscopy (LM- Union Optical Co., Ltd., Tokyo, Japan) and X-ray diffraction (XRD- PW 1729, Philips, Eindhoven, The Netherlands). SEM and LM observations were carried out after mechanical polishing of the sample surface and etching by means of Vilella reagent. XRD patterns were collected in the 20 angular range 15-60\({}^{\circ}\) by using the Mo-K\(\alpha\) radiation (\(\lambda\) = 0.070926 nm) with 20 steps of 0.05\({}^{\circ}\) and counting time in steps of 2 s. From the relative intensities of the peaks in each pattern the crystalline texture was evaluated. The dislocation density \(\rho\) was determined from precision peak profiles recorded with 20 steps of 0.005\({}^{\circ}\) and counting time in steps of 4 s. After background subtraction the peak profiles were fitted by Lorentzian curves to eliminate the K\(\alpha\)2 component, then the full width at half maximum (FWHM) was corrected from the instrumental broadening to get the total broadening (\(\beta_{T}\)) that is the sum of two contributions due to the size (\(D\)) of coherently diffracting domains (\(\beta_{D}\)) and the micro-strains (\(\beta_{\epsilon}\)) induced by dislocations:  
\[\beta_{T}=\beta_{D}+\beta_{\epsilon}=\frac{0.89\lambda}{D\cos\theta}+2\epsilon \tan\theta \tag{1}\]  
where \(\theta\) is the [PERSON]'s angle of the XRD peak. To determine the two contributions, \(\beta_{D}\) and \(\beta_{\epsilon}\), the Cauchy procedure was used by plotting \(\beta_{T}\) cos\(\theta\)/\(\lambda\) vs. sin\(\theta\)/\(\lambda\). The dislocation density \(\rho\) was then calculated through the Williamson-Smallman relationship [54]:  
\[\rho=\frac{\Xi\epsilon^{2}}{Fb^{2}} \tag{2}\]  
where \(\Xi\) = 16.1 a constant, \(F\approx 1\) a factor depending on the interaction of dislocations and \(b\) = 0.248 nm the modulus of Burgers vector. The mechanical properties were investigated through Vickers hardness and FIMEC (Flat-top cylinder Indenter for Mechanical Characterization) tests. FIMEC is an instrumented indentation test employing a cylindrical punch and its typical characteristics have been described in detail in many papers (e.g., see [19; 55; 56]). In the present study FIMEC was used to measure the yield stress YS and the reported data are the mean values of three tests. Vickers hardness tests were made by means of a HV50 (Remet, Bologna, Italy) instrument by using a load of 5 kg. Three hardness tests were made on each sample in the central zone of the longitudinal cross-section. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Cr** & **C** & **Mn** & **V** & **W** & **Ta** & **Ti** & **N** \\ \hline
8.93 & 0.12 & 0.47 & 0.2 & 1.07 & 0.14 & 0.009 & 0.018 \\ \hline
**P** & **S** & **B** & **Si** & **Nb** & **Mo** & **Ni** & **Cu** \\ \hline \textless{}0.005 & 0.004 & \textless{}0.001 & 0.006 & 0.002 & 0.0015 & 0.002 & 0.003 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Nominal chemical composition of EUROFER97 steel (wt.%) (Fe to balance) [1].