Investigation on residual stresses and fracture behaviour of cladded plates with defects

Cladded pressure vessels and pipes made from ferritic steels with an austenitic cladding are widely used in power plant components. The fracture mechanics assessment of these components is a challenging task due to the different failure mechanisms of the dissimilar bonded materials and the complex residual stress field caused by the welding process and the thermal mismatch. The present study is concerned with an experimental and numerical investigation of sub-clad and surface flaws in ferritic cladded plates. The cladding process and the subsequent heat treatment were performed in accordance with the relevant standards. The plates were tested under combined mechanical and restrained thermal loading conditions until complete failure. The local conditions leading to crack initiation an d arrest were determined in numerical analyses of the experiments. At first, the residual stress field due to the cladding process was determined by numerical simulations of the welding and heat treatment processes. Subsequently, the fracture tests were simulated. From the results it can be shown that crack initiation in the base metal is the more critical event compared to ductile failure of the austenitic cladding. Moreover, the cladding might provide a non-negligible stress relief of the respective component.