Modelling precipitate distribution in reduced-activation steels

The microstructure and carbide distribution in two commercial creep resistant, low-activation, martensitic alloys (F82H and JLF-1) have been modelled using a thermo-kinetic calculation package. The microstructures after manufacturing and after long unstrained thermal aging treatments (13 500 h) at various temperatures (250, 400 and 550 °C), considered to be representative of service temperatures, have been considered. In all cases, the calculated carbide size distributions match in order of magnitude experimental measurements, although the shape of the distribution differs. The obtained results are more accurate for alloy F82H than for alloy JLF-1. Nevertheless, this work shows that it is possible to obtain realistic estimates of the microstructure evolution of creep resistant alloys in long thermal ageing treatments at service-like temperatures.