GRAIN BOUNDARY PHOSPHORUS SEGREGATION UNDER IRRADIATION AND THERMAL AGEING AND ITS EFFECT ON THE DUCTILE TO BRITTLE TRANSITION FOR 2.25CR 1MO STEEL

摘要

Embrittlement of low alloy steel components used in the nuclear power industry is classified into hardening embrittlement and non-hardening embrittlement. Hardening embrittlement stems from point defect damage and precipitation of carbides or copper-rich compounds. Non-hardening embrittlement results mainly from grain boundary segregation of phosphorus. To examine the non-hardening embrittlement in 2.25Cr 1MO steel, phosphorus intergranular segregation in samples subjected to neutron irradiation and thermal ageing at 270 and 400℃ is determined by modelling and transmission electron microscopy. The ductile to brittle transition temperature for the steel is determined by means of small punch testing with 3mm diameter disc and mini-notched impact specimens. It is indicated that there is a reasonable agreement between the behaviour of intergranular phosphorus segregation and shifts in the ductile to brittle transition temperature.