J-R Behaviour of 20MnMoNi55 Pressure Vessel Steel

Abstract

Material of Reactor Pressure Vessel (RPV) should have good fracture toughness to ensure safe operation of nuclear reactor. In order to be on safe side the fracture characteristics of RPV material have to be quantified. In this present work the fracture characteristics of 20MnMoNi55 steel – the material used for Indian PHWR – have been found using J-Integral test. The microstructures of the steel and its relevant mechanical properties such as hardness and tensile properties have been characterized. Monotonic J-R curves of the material have been determined in the temperature of and . Fracture behaviour under quasi-static tearing load has been studied through fracture toughness tests on 20MnMoNi55 steel using Compact Tension(CT) specimens of Width(W)=50 mm and thickness(B)=20 mm. J-R curves were obtained from specimens precracked to. The single specimen unloading compliance method have been used for generating J-R curves. Stretch zone widths (SZW) were measured on the fractured surfaces of broken specimens. The stretch zone dimensions that were determined have been used in conjunction with the experimentally derived J-R curve to obtain a value of the ductile fracture toughness parameter . The initiation toughness, , obtained at the intersection of the blunting line and the power-law fit to the J-R curve, and the critical toughness, , determined following the procedure of the ASTM standard, were estimated. The results of fracture studies under monotonic loading infer: (a) the material exhibits high fracture resistance at room temperature (b) the fracture resistance of the steel deteriorates at a temperature of as compared to room temperature, the deterioration in the fracture properties has been attributed that steel exhibits embrittlement tendencies operative in this temperature. (c) The stretch zone formation is very prominent and starting/ending points are clearly discernible in 20MnMoNi55 steel. The correlation of , critical toughness, and initiation toughness, , has been examined with a view to ascertain the applicability of the stretch zone dimension for measurement of fracture toughness.