Grain-boundary segregation of impurity elements, such as phosphorus, arsenic, antimony, and others,
decreases the grain-boundary cohesion, which can substantially increase the temperature of the
ductile-brittle transition in low-alloy structural steel. The most dangerous surface-active impurity for
low-alloy steel employed for nuclear reactor vessels is phosphorus. A change of the cohesive strength of
grain boundaries as a result of radiation-stimulated phosphorus segregation is considered to be one of the
main mechanisms determining the radiation embrittlement of reactor-vessel materials. Since the
mechanisms of embrittlement during development of reversible temper brittleness and radiation-stimulated
grain-boundary segregation of phosphorus are the same, the main characteristics of the influence of the
latter on the mechanical properties of steel can be determined by investigating steel treated in the range
400–600°C. The present investigation made it possible to develop a relation for determining the change in
the temperature of the ductile-brittle transition in low-alloy steel as a result of the development of temper
The effect of grain boundaries on fracture is one of the oldest and most difficult problems of material science.
Boundaries can impede the motion of cracks, but ordinarily they promote the growth and propagation of cracks. A change in
the mechanism of fracture from intragrain fracture to fracture along grain boundaries is usually accompanied by a sharp
degradation of the mechanical properties – an increase of the temperature of the ductile-brittle transition and a decrease of
the fracture stress and plasticity of steel. Fracture starts before the margin of strength and plasticity of the material is exhaust-
ed. Moreover, the sensitivity to intergrain fracture sharply increases with increasing strength of the alloys employed, for
example, in the case of radiation-induced hardening of steel.
Grain-boundary segregation of impurity elements, such as phosphorus, arsenic, antimony, and others, decreases
grain-boundary cohesion, which can substantially increase the temperature of the ducitle-brittle transition in low-alloy struc-
tural steel [1–3]. The most dangerous surface-active impurity for materials used in nuclear reactor vessels is phosphorus .
The content of other surface-active impurity elements in such steel is much lower and the diffusion activation energy is much
higher than that of phosphorus, so that their influence on grain-boundary embrittlement can be neglected. The change in the
cohesive strength of grain boundaries as a result of radiation-stimulated segregation of phosphorus is considered to be one of
the main mechanisms determining the radiation embrittlement of reactor vessel materials. Grain-boundary segregation of
phosphorus can occur in the range 400–600°C, for example, during slow cooling from the high-temper temperature or dur-
ing special isothermal treatment at an appropriate temperature. The phosphorus-segregation-induced decrease of
Atomic Energy, Vol. 91, No. 1, 2001
GRAIN-BOUNDARY SEGREGATION OF
PHOSPHORUS IN LOW-ALLOY STEEL
A. V. Nikolaeva,
Yu. A. Nikolaev,
and Yu. R. Kevorkyan
Translated from Atomnaya Énergiya, Vol. 91, No. 1, pp. 20–27, July, 2001. Original article submitted January 26,
2000; resubmitted November 24, 2000.
2001 Plenum Publishing Corporation
Institute for Nuclear Reactor Safety.
Russian Science Center Kurchatov Institute.