Development of a Residual Lifetime Prediction Methodology for Creep and Fracture Behaviour of Ferritic-Martensitic Steels Using Small-Punch Testing Technique

The main aim of the thesis is to demonstrate the suitability of Small Punch (SP) testing for lifetime prediction of metallic materials operating at high temperatures. The lack of standardisation of this technique and doubts about the correlation of the data with that obtained from conventional creep tests, supports the need to exploit the recently launched Code of Practice for Small Punch Testing (CEN/WS 21). The present work is specifically concerned with investigating the creep behaviour of P91 steel weldments at 600oC along with low-temperature fracture behaviour. Thin discs, 8mm in diameter and 0.5mm thick, were manufactured from different zones of a component containing a P91 welded joint: base metal (BM), service exposed material (SE), weld metal (WM), fine-grain and coarse-grain heat affected zones (FG-HAZ & CG-HAZ). The results of SP creep tests on these disks, performed at 600oC under different loads carefully following the Code of Practice, could be correlated with standard creep data. The SP test is shown to be a reliable method to depict creep behaviour of this alloy and its weldments and a creep model derived, useful for life time prediction, could also be demonstrated through FEA to predict the creep deformation of the SP discs. Additionally, the SP testing method shows potential to evaluate the fracture properties of P91 weldments, in particular the ductile-to-brittle transition temperature and fracture toughness estimations.JRC.F.4-Safety of future nuclear reactor