Influence of Long-Term High-Temperature Action on the Impact Toughness of the Base Metal and the Weld Metal of the 22K Steel Welded Joint

Abstract: One of the applications of construction low-carbon 22K steels (AISI 1022 type) is used as a material for the body of a core catcher (CC) for nuclear power plants with water-cooled reactors (WCRs). In the event of a severe beyond design-basis accident, the CC vessel will be under conditions of prolonged high-temperature impacts, which can significantly change the structural state and lead to degradation of the mechanical properties of the vessel material. The data on the effect of such actions on the mechanical properties and fracture resistance of welds (its properties usually differ from those of the base metal) from low-carbon steels are very limited in the literature, which makes it difficult to guarantee the reliability and safety prediction of CC. The purpose of this work was to carry out comparative Charpy V-notch impact tests of samples of the base metal and the weld metal of the 22K steel welded joint before and after long-term high-temperature heat treatment, simulating the thermal effect in the conditions of a severe accident on the material of the NPP vessel. Welded joints of 22K steel sheets were obtained by the method of automatic argon-arc welding with a consumable electrode (welding wire SV-08G2S was used) in accordance with Rules and norms in nuclear industry PNAE G-7-009–89. Based on the test results, the ductile–brittle transition curves were plotted and the analysis of fracture of the samples was carried out. The influence of structural factors on the KCV impact toughness has been studied. It is shown that prolonged high-temperature exposure leads to an increase in the temperatures of the beginning and end of the ductile-brittle transition by 30–50°C and to an expansion by 15–25°C of the temperature range of the ductile-brittle transition of both the base metal and the weld metal of the welded joint. © 2021, Allerton Press, Inc.