# Grain Refinement and Improved Mechanical Properties of EUROFER97 by Thermo-Mechanical Treatments
## 4 Conclusions  
This work reports preliminary results of an extended experimental campaign aimed at improving the strength of EUROFER97 steel through microstructure refining without introducing detrimental effects on its ductility. From the as-supplied material prepared through the standard treatment, 40 different groups of samples were obtained by combining cold rolling with five CR ratios and eight heat treatment temperatures. The results of microstructural examination and mechanical tests can be summarized as follows.  
Cold rolling leads to grains of smaller size elongated along the rolling direction, the nearly random texture evolves towards a cubic [100] one with a secondary [211] component, and dislocation density increases. As expected, such microstructural changes, which are more relevant for greater CR ratios, induce a progressive strengthening of the material.  
Recrystallization takes place in heat-treated samples with kinetics depending on treatment temperature and CR ratio. In the samples with CR of 80% at 650 \({}^{\circ}\)C, a population of equiaxed grains of sub-micrometric size was observed indicating that the primary recrystallization was completed. Higher treatment temperature in these samples induced abnormal grain growth.  
The hardness of all the examined samples decreased as heat treatment temperature increased and the variation is more pronounced in the samples cold-rolled with greater CR ratios. Except for the samples deformed with CR ratio of 20%, it dropped below that of standard EUROFER97 for treatments above a critical temperature (700 \({}^{\circ}\)C if CR \(\geq\) 50%, 750 \({}^{\circ}\)C for lower CR).  
On the basis of these results, tensile tests were performed on selected samples (CR ratio of 80%, treatment temperatures of 400, 500, 600 and 650 \({}^{\circ}\)C). In comparison to standard EUROFER97, the treatment at 650 \({}^{\circ}\)C leads to an increase in YS around 12% while the total elongation was nearly the same (-22%). On the contrary, after heat treatment at lower temperatures (400, 500 and 600 \({}^{\circ}\)C) YS and UTS were significantly larger but the steel had lower ductility.  
In conclusion, this work demonstrated the feasibility to strengthen EUROFER97 steel without compromising its ductility. The result is promising for nuclear fusion applications and the completion of microstructural analyses and mechanical tests of all the prepared samples will allow us to identify the most effective process parameters.  
Conceptualization, G.S., R.M. and A.D.S.; methodology, G.S., R.M., A.D.S. and C.T.; formal analysis, G.S., R.M., S.M. and A.V.; supervision, R.M. and C.T.; draft paper preparation, G.S., R.M. and A.D.S.; final paper preparation, all authors. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training program 2014-2018 and 2019-2020 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors are grateful to [PERSON] of the Department of Industrial Engineering--University of Rome \"Tor Vergata\" for the assistance in sample preparation.  
**Conflicts of Interest:** The authors declare no conflict of interest.