Toughness of SA738Gr.B steel used for nuclear containment vessel

Abstract

Toughness of structural steels is as important as the strength, but much more complicated partly due to the diversity of the characterization methods and the inconsistency among the obtained results. In the present work, the toughness of SA738Gr.B steel plates of 55 and 130 mm thicknesses used for building the containment vessels (CV) of third-generation nuclear power plants, in the quenched and tempered (QT) and simulated post-weld heat treatment (SPWHT) states, was thoroughly characterized by measuring the Charpy impact energy, nil-ductility temperature, fracture toughness and fatigue crack growth rate. Attention was paid to the distinction between these toughness indicators in terms of crack initiation and propagation, and on their correlations in an attempt of proper and combined use of the test values. It is shown that the toughness of the 55 mm thick plate is excellent and does not change significantly across the thickness in either heat treatment condition. Therefore the plate can be reliably used for building the head and shell of the CV. The 130 mm thick plate exhibits larger variation in toughness across the thickness, and is only suitable for fabricating the accessory parts of the CV. Moreover, the existing relationships between the toughness indictors gained from Charpy impact tests and drop weight tests or fracture toughness tests are no longer valid for modern steels such as SA738Gr.B, as the harmful elements and inclusions that significantly influence the initiation of cracks have been notably removed in processing the steel.