CARBON REDISTRIBUTION BETWEEN AN AUSTENITIC CLADDING AND A FERRITIC STEEL FOR PRESSURE-VESSELS OF A NUCLEAR-REACTOR

In this work, carbon redistribution between an austenitic cladding and a ferritic-carbidic steel for pressure vessels of the Voronez water energy nuclear reactor is studied. The carbon concentration in the surroundings of the weld interface was determined by electron beam microanalysis. The method of line segment analysis, with the help of Fe-C standards, used in this work enabled the correct determination of the total carbon content and its dependence on the distance from the weld interface. The diffusion study was carried out in the temperature interval from 500 to 750-degrees-C, on experimental weldments prepared by resistance welding and on a submerged-arc strip weldment used in technical practice. The carbon diffusion in the weldments was described by a diffusion model assuming two separate carbon diffusion coefficients D- and D+ of the left- and the right-hand part of the weldment respectively. While D- = 2.7 x 10(-5) exp(-164/RT) m2 s-1 agrees well with the carbon diffusion coefficient in austenite, D+ = 1.2 exp(-209/RT) m2 s-1 corresponds to the effective carbon diffusion coefficient in the ferrite-carbide mixture. It has been shown that the results obtained on the experimental weldments can be applied to the technical weldments and enable the prediction of carbon redistribution during post-weld heat treatment and application.