Influence of structural parameters on the tendency of VVER-1000 reactor pressure vessel steel to temper embrittlement

In this paper the influence of structural parameters on the tendency of steels to reversible temper embrittlement was studied for assessment of performance properties of reactor pressure vessel steels with extended service life. It is shown that the growth of prior austenite grain size leads to an increase of the critical embrittlement temperature in the initial state. An embrittlement heat treatment at the temperature of maximum manifestation of temper embrittlement (480 °C) shifts critical embrittlement temperature to higher values due to the increase of the phosphorus concentration on grain boundaries. There is a correlation between phosphorus concentration on boundaries of primary austenite grains and the share of brittle intergranular fracture (that, in turn, depends on impact test temperature) in the fracture surfaces of the tested Charpy specimens.

► The critical brittleness temperature (Tk) in the initial state increases with the grain size.
► The fraction of brittle intergranular component (η) depends from test temperature.
► The value of η correlates with the phosphorus concentrations on boundaries (Cp).