Forecasting in the presence of microstructural changes for the case of P91 steel after long-term ageing

The statistical analysis of experimental data was presented and the precipitate diameter forecast for selected steel grade was developed in this paper. The investigations of changes in the material microstructure were carried out under high-temperature conditions. Therefore, this material was characterised by increasing instability over time. Long-term ageing tests were carried on P91 steel for 10³, 10⁴, 3 × 10⁴ and 7 × 10⁴ h at 600 and 650 °C. The recorded microstructure images allowed the quantitative analysis of precipitates that occur mainly at the former austenite grain boundaries and martensite laths. The statistical distribution forecast was developed for the ageing time of 10⁵ h. The forecasting under the conditions of material structure changes requires repealing classic assumptions adopted in the theory of prediction. Such methodology was proposed in this article. This article is the basis for the development of further research in this field. The proposed methodology can be used for diagnostic purposes and in the equipment failure risk assessment.