NUMERICAL INVESTIGATIONS ON THE RESIDUAL STRESS FIELD IN A CLADDED PLATE DUE TO THE CLADDING PROCESS

The inner surface of reactor pressure vessels is protected against corrosion by an austenitic cladding. Generally, the cladding is welded on the ferritic base metal with two layers to avoid cracks under the cladding and to improve the microstructure of the cladding material. On the other hand, due to the cladding process and the difference of the thermal expansion coefficient of the austenitic cladding and the ferritic base material, residual stresses are acting over the wall thickness. This residual stress field is important for the integrity assessment of the component. For the determination of the residual stress field, plates of a reactor pressure vessel steel were cladded by submerged arc welding and heat treated, representative of the real component. The numerical simulation was performed with the finite element code SYSWELD. The heat source of the model representing the welding process was calibrated against the temperature profiles measured during welding. In the analysis, the temperature-dependent material properties, as well as the transformation behaviour of the ferritic base metal, were taken into account. The calculated residual stresses show tensile stresses in the cladding followed by compressive stresses in the base metal that are in agreement with measurements with X-ray diffraction technique. After post-weld heat treatment the residual stresses in the ferritic base metal are reduced significantly.