Effect of Irradiation on the Elasto-Plastic Toughness of Pressure Vessel Steels

Abstract

A study on the effect of irradiation on the toughness of pressure vessel materials in the ductile regime has been undertaken. Compact tension (CT) specimens of two pressure vessel steels (A533 B and A508 Class 3) and a weld material of fitting chemical composition were irradiated and received neutron fluences of 3 and 8 × 1019 n/cm2. The J-R curves of these materials were determined between 100 and 290°C. Only a very small influence of irradiation was observed for tests at 290°C. In irradiated condition, the effect of the test temperature is not noticeable. At lower temperature, but in the ductile regime, the weld material appears to be more sensitive to neutron irradiation than the two steels. The forged material exhibited a surprisingly high shift of transition temperature since cleavage rupture occurred up to 100°C. A method using tension tests on round notched specimens with different root radii was employed to obtain an alternative value of Jc. This method relates the Jc value to a critical growth of cavities that is determined from the tension test on notched specimens. A good agreement between this method and the conventional one was obtained for the A533 B steel. For the forged material, the results were more questionable and this was attributed to inhomogeneities in the distribution on nonmetallic inclusions for this material. This method is expected to be very useful for the determination of Jc for irradiated materials.