Design of new Fe–9CrWV reduced-activation martensitic steels for creep properties at 650 °C

New low-activation martensitic steels for creep resistance between 600 and 700 °C were designed using thermodynamic, kinetic and neural network modelling tools. Suitable compositions for a matrix stabilised by vanadium nitride (VN) particles were firstly suggested on the basis of phase stability calculations using the thermodynamic software MTDATA. A neural network method was then used to predict the creep rupture stress of the possible compositions. It was predicted that a creep rupture stress close to 100 MPa for 100 000 h at 650 °C could be achievable. Finally, the precipitation and growth kinetics of VN were calculated using an existing kinetic model. These calculations suggested that a fine (nanometre-scale) and homogeneous distribution of particles could be obtained using a high nucleation site density. This could, in principle, be achieved using thermomechanical treatments and should be even better than alloys produced using the classical normalization and tempering route.