Weldability of advanced EU-developed steels

The establishment of the joining technology such as welding is important milestone in the development of new  materials and technological solutions for components. New grades of EUROFER steel [1, 2] are currently under development for application in International Thermonuclear Reactor ITER [3] (for test blanket module) and future power plants to sustain the harsh conditions at operation such as high temperature combined with fast neutron irradiation. The superior properties of the developed EUROFER grades are due to  tailored and optimized microstructure as for instance seeded MX carbo-vanadium-nitrides [4, 5] and also achieved by optimized thermomechanical treatment. Welding technologies require higher temperature and therefore cause specific microstructure in the welded joints itself and often undesirable modifications of the microstructure in heat-affected zone (HAZ).  Optimization of the welding parameters as filler materials and post-weld heat treatments are performed to remediate the microstructure of the joints to provide the desired thermomechanical properties and to reduce/exclude formation of the welding defects as for instance heat cracks. However, the means of post-welding heat treatment (PWHT) are limited in comparison with the thermomechanical treatments used for fabrication of steels due to technological limitations for the fabrication of nuclear components. The underlying processes of microstructrural changes  during welding and PWHT are sophisticated and still to be understood for the new grades of EUROFER steel. 

The main goal of this PhD work is to develop an understanding of the physico-chemical processes of weld/HAZ microstructure formation and its relation with the thermo-mechanical properties. This understanding will help to establish the scientific basis for the optimization of welding and PWHT processes. The work will be performed with Gleeble, which is Thermal-Mechanical Physical Simulation System and will be guided by modeling with Thermocalc software. The joints will be created and characterized using dilatometers. The mechanical and microstructural properties of the obtained joints will be characterized to select the most promising joints for subsequent neutron irradiation exposure (to perform in BR2 reactor, Mol, Belgium) to investigate the effect of irradiation damage. The project will be hosted at the Belgium Nuclear Research Center, Mol in close collaboration with OCAS NV [6] (Belgium steel making industry), and University of Ghent (delivering PhD degree).

 [1] https://publikationen.bibliothek.kit.edu/270055720/3814432

[2] https://www.osti.gov/servlets/purl/1564234

[3] https://www.iter.org/newsline/183/784

[4] A. Puype et al., Effect of processing on microstructural features and mechanical properties of a reduced activation ferritic/martensitic EUROFER steel grade, J. Nucl. Mater. 494 (2017) 1-9. https://doi.org/10.1016/j.jnucmat.2017.07.001

[5] O. Kachko et al., Development of RAFM steels for high temperature applications guided by thermodynamic modelling, Nuclear Materials and Energy 32 (2022) 101211. https://doi.org/10.1016/j.nme.2022.101211

[6] https://www.ocas.be/

The minimum diploma level of the candidate needs to be

• Academic bachelor
• Master of sciences
• Master of sciences in engineering

The candidate needs to have a background in

• Physics
• Knowledge in material science, knowledge in nuclear materials

Estimated duration

Expert group