Mechanical Properties Distribution in Welds and Forging of VVER-1000

Study of weld metal and shell metal of VVER-1000 reactor is carried out. Metal of the control welded joint performed to the welds Nos. 3 and 4 and metal of the test ring of supporting shell is used. For each of the analyzed materials the bending tests of Charpy specimens are carried out according to the surveillance specimens testing procedure. Fabrication of specimens and all the tests are performed by TK “OMZ Izhora”, ltd. Leadership of the tests and assessment of brittle-to-ductile transition temperature is performed by RRC “Kurchatov Institute”. It is shown that guaranteed values of brittle-to-ductile transition temperature (T_K0) for VVER-1000 pressure vessel materials (0°C for weld and −25°C for base metal [1]) are the conservative estimation of T_K values obtained for all groups of the tested specimens. However in some cases such estimation is super conservative. Assessment of distribution of brittle-to-ductile transition temperature (T_K) values of the weld in radial direction has shown that T_K varies from layer to layer in the range from −55 to −22°C. Variations of T_K values are conceivably random and not connected with changes of the chemical composition of metal. It is shown that the situation is possible when brittle-to-ductile transition temperature of “inner grooving” weld metal is higher than that of the “outer grooving” weld metal. This result should be taken into account when planning the surveillance specimens programmes. Metal of “inner grooving” should be included in surveillance specimens. While assessing the T_K values distribution in axial direction it has been determined that the maximum brittle-to-ductile transition temperature is specific for the area adjacent to the line of weld-to-base metal alloying. This effect is stably observed already at a distance of 8 mm from the alloying line. Study of distribution of T_K values of supporting shell metal has shown that for the analyzed supporting shell the maximum brittle-to-ductile transition temperature value corresponds to the inner side of the shell middle third, the minimum value — to the shell inner surface. On the whole, shell metal is characterized by rather low values of brittle-to-ductile transition temperature.