Quantification of the toughness distribution in a heavy section submerged are multilayer reactor pressure vessel weldment

In a working procedure qualification test weld representing a heavy section circumferential reactor pressure vessel (RPV) weld tested in 1968, lower t oughness values were observed in the top layer region compared to those fou nd in the filler region. Gleeble simulation, extensive microscopic evaluati on. diligent Charpy V-notch testing and modelling of the bead sequence and distribution of alloying elements was applied to explain this effect. It co uld be revealed that the microstructure of the weld metal is the most impor tant factor influencing the toughness. When an 'as welded' microstructure i s partly or fully reaustenitised by the adjacent multilayer beads, the micr ostructure transforms and the toughness increases. In the filler region, 85 % of the cross-section consists from transformed microstructure, whereas in the top layer only 20% are transformed. It is quite evident that, accident ally, the notch tip of Charpy samples in 1968 were placed in untransformed microstructures. When the top layer on the inner surface of the RPV is weld cladded by austenitic stainless steel, full transformation occurs and the toughness representing the filter region can be taken into account for safe ty evaluations. (C) 1999 Elsevier Science S.A. All rights reserved.