In-service embrittlement of pressure vessel steels

A survey is presented of the characteristics of the processes of structural degradation of low alloy steels for pressure vessels of nuclear reactors. These are either processes which do not change the micromechanism of embrittlement, processes which partly change this micromechanism (as a result, the initiation of brittle fracture takes place due to the combined effect of intergranular failure and transgranular fission) or processes which totally change the micromechanism of failure. Briefly described are the types of mechanical tests used for the research of embrittlement: tensile tests, bending impact and methods of fracture mechanics. Some results of the research of heat embrittlement of low alloy steels are given in graphs and the consequences thereof for technical practice are summed up. A new type of steels will have to be introduced which are extremely resistant to heat aging. In existing steels it will be necessary to adjust chemical composition and production such as to significantly reduce their susceptibility to heat aging. In operating installations where a certain degree of degradation has already taken place the main task will be to determine the residual life. (Z.M.). 10 figs., 1 tab., 23 refs