Basic mechanical and metallurgical characteristics of half-finished WWER-1000 pressure vessels as manufactured by SKODA Plzen

Experience gained in Skoda Works with respect to the manufacture of half-finished products for the welded body and lid of a WWER-1000 pressure vessel is summarized. Steel for the pressure vessel, 15Kh2NMFA, is produced in three quality classes: the lowest for rings to be located off the reactor core region, higher for the vessel lid and bottom cap compacts, and the highest for three rings to be located within the reactor core region. The vessel is manufactured from forged half-products. Experience shows that after the basic heat treatment, i.e. hardening and high-temperature drawing to 650 degC, and at a wall thickness not exceeding 330 mm, the 15Kh2NMFA steel possesses the bainitic structure with no proeutectoid ferrite. The latter does not pose serious problems in the half-finished lid ring 680 mm thick either. The maximum admissible inclusion content, which is given by degree 3.5 for sulfides, oxides as well as silicates, can be obeyed. Plots are shown of the basic mechanical properties of the half-finished products during their heat treatment as a function of their thickness. (Z.M.). 4 figs., 4 refs