Development of new reduced activity ferrite martensite steels with higher temperature capability and improved impact properties – Materials Strand Project

Supervisors: Prof Mark Rainforth (lead) (University of Sheffield), Prof EJ Palmiere (University of Sheffield).

Fusion power reactors feature a high heat flux loading of the plasma facing components (PFC) referred to as the “first wall” and “blanket”. PFC components must have high temperature resistance and high thermal conductivity. The concept of reduced-activation ferritic/martensitic (RAFM) steels was proposed in 1982 and was based largely on the conventional ferritic/martensitic (FM) steels used in fission reactors, Mod9Cr–1Mo (Grade P91, ASME Section II), by replacing Mo with W and Nb with Ta to meet the shallow land burial limitation. RAFM steels are advantageous compared to austenitic stainless steels (such as 316LN) as they exhibit lower radio activation levels (no Ni), better thermal conductivity (less Cr), lower thermal expansion ratio, and superior swelling resistance [1].

RAFM steels were primarily developed with 8–9 weight percentage (wt %) chromium (Cr) because steels with that Cr content exhibited the minimum shift in radiation-induced ductile-to-brittle transition temperature (DBTT). In addition to the impurity limits for conventional FM steels to prevent property impairment—e.g., the effects of P, S, and Si on toughness, there are strict limitations on impurity levels in RAFM steels (e.g., Ni, Co, Cu, Nb, Mo, Ag) to meet the criterion of low activation for shallow land burial of nuclear waste. A higher-Cr and lower-tungsten composition grade, called Eurofer97 (9Cr–1WVTa), was adopted by the EU in 1997 for its improved corrosion resistance and neutron efficiency. Thereafter, the development of other variant RAFM steels—such as CLAM (China low activation martensitic), INRAFM of India and ARAA (advanced reduced-activation alloy) of Korea—was initiated, with compositions similar to Eurofer97.

The aim of this project is to design new reduced activation ferrite martensite (RAFM) steels with minimised radiation-induced ductile-brittle transition temperature (DBTT) shift and enhanced high temperature creep strength during simulated service irradiation. This will require grain size refinement and the production of thermally stable nano-scaled precipitation, based around MX, with a minimisation of M23C6. This will be achieved through a) optimisation of the thermomechanical processing route (known as ausforming) to refine grain size by dynamic recrystallisation and/or strain-induced ferrite transformation; and b) through composition optimisation, particularly through the use of high nitrogen content and later the addition of boron.

The project will be based in Sheffield, but there is the opportunity to travel to conferences and for collaboration with groups at UKAEA, Birmingham and Swansea

This project is offered by University of Sheffield. For further information please contact:

This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.