Austenite grain growth in a nuclear pressure vessel steel

There is uncertainty on the physical significance of models applied to the coarsening of austenite grains in nuclear pressure vessel steels. As a result, new data are generated and analysed by adapting standard theory to account for the initial austenite grain size generated when the steel becomes fully austenitic, and any growth during heating to the annealing temperature. The experimental data reflect two regimes of isothermal grain coarsening, with grain boundary pinning dominating the kinetics at temperatures below about 940 °C. The precipitates responsible for this pinning have been identified using thermodynamics, high-energy X-rays, transmission electron microscopy and microanalysis as aluminium nitrides. The model accounting for all these factors seems to generalise well on unseen data.