As curly as 1942 it was recognized that high-energy neutrons would have the ability to disrupt the crystal lattice of metals through which they might pass and that this disruption might lead to serious changes in the mechanical and physical properties of structural materials used in the construction of nuclear reactors. Since that time studies of these “radiation effects” have been conducted by solid stale physicists and by reactor development engineers working at or in conjunction with the various atomic energy installations. This paper is a survey of the published literature on the effect of neutron radiation on the mechanical properties of steels.
On theoretical grounds and on the basis of fundamental experiments it is postulaled that clusters of radiation-produced vacancies or interstitials, by interacting with dislocations already present and additional dislocations produced during plastic deformation, are primarily responsible for the increased strength and decreased ductility of irradiated metals.
From a tabulation of the existing information on the effect of neutron radiation on the mechanical properties of carbon, alloy, and stainless steels, it appears that relationships between the changes in properties and neulron exposure can be defined. These relationships indicate that steels behave in general as a class of material and are affected by neutron radiation in a similar manner so that the effects of a given neutron exposure can usually be predicted within rallier general limits.
Normally, a large proportion of the radiation-produced crystal lattice defects responsible for the changes in mechanical properties in steels can be removed by heating in the range 550 to 900 F. Likewise, irradiation at temperatures above 500 F usually results in less damage than irradiation at lower temperatures, presumably because of concurrent thermal annealing of the damaged regions. Under certain conditions, radiation may accelerate phase transformation or aging phenomena, and changes in mechanical properties as a result of such secondary effects may not be removed by the annealing treatments at 550 to 900 F.
It is important to recognize that the above generalizations are based on results which show considerable scatter and that there is information available which indicates that such factors as grain size, microstructure, composition, and steel cleanliness can influence the magnitude of the radiation effect.