Examples of the evolution of materials for nuclear applications: metallurgical improvement of 16MND5 steel and new technologies for manufacturing heavy components

Abstract

Creusot-Loire Industrie has been constantly improving and adjusting the quality of its products (heavy forgings, castings or plates) based on knowledge of their in-service behaviour. The development of steel manufacturing techniques has been oriented to increasing the quality of steel, in particular by reducing drastically the impurity content (S, P), by better control of the basic range of chemical composition, and by decreasing the gas content (N, H, O). Changes in ingot shapes have been made to optimize the quality of the steel with respect to segregation (development of hollow and LSD ingots to reduce the effect of irradiation embrittlement at the inner surface and sub-surface area). The effects of these developments on the toughness of nuclear materials are illustrated by two examples: 16MND5 steel used for pressurized water reactors; ASTM A350LF5 steel used for cask bodies for the transport of irradiated fuel elements. Modifications in hot working (mainly forging) procedures have enabled the development of products with shape adapted to easier construction and/or best quality and/or reduction in the number of welds, thus decreasing the construction and in-service inspection costs. New forging products to be used in nuclear pressurized water reactor power plants are presented. © 1994.