Metallographic quality of inner surfaces of rings for WWER nuclear reactor pressure vessels

Metallographic quality of steels for WWER-440 and WWER-1000 reactor pressure vessels was examined on samples from 25 heats. The chemical composition invariably lay within the required range, only the sulfur content was in several cases slightly elevated. The occurrence and amounts of sulfidic segregates were also investigated in view of the fact that during surfacing, they can induce formation of cracks beneath the overlay. Changes in the chemical composition of the steel in the site where segregate occurred were determined quantometrically over an area 5 mm in diameter; increased Mn, P, S, Cr, Mo, Sb, As and Sn levels were observed, while the carbon content in the segregate site could not be so far determined reliably enough. Since the formation of sulfidic segregates in large-size ingots cannot be prevented by technological means, the conditions for surfacing the austenitic layer in the upper part of the pressure vessel ring must be adapted to this poorer metallurgical quality of the steel surface. (Z.M.). 3 figs., 1 tab., 3 refs