GRAIN-BOUNDARY EMBRITTLEMENT DUE TO REACTOR PRESSURE-VESSEL ANNEALING

The tendency of the Cr-Ni-Mo low-alloyed steel to brittle fracture as a function of the sizes of austenitic grains and the phosphorus concen tration at the grain boundary has been studied. A simple analytical de pendence connecting the temperature of ductile-to-brittle transition o f steel with the boundary phosphorus concentration and the austenitic grain size has been found. In estimating the kinetics of the developme nt of intergranular embrittlement the decrease in the diffusion coeffi cient of phosphorus in alpha-Fe in the presence of molybdenum was take n into account. The effect of the mutually increasing grain boundary a dsorption of phosphorus and nickel was considered as well. The possibi lity to predict the tendency of the Cr-Ni-Mo low-alloyed steel to temp er embrittlement is shown. The technique proposed was successfully use d to estimate the degree of recovery of the Ni-containing materials of the nuclear reactor vessels after annealing radiation defects.