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The effect of interstitials and more particularly of nitrogen on the radiation-induced brittleness and mechanical property changes of iron is investigated by comparing the behavior of iron of technical purity remelted in vacuo and enriched with titanium to block interstitials as stable precipitates, and of iron with about 0.01 weight per cent carbon and 0.02 weight per cent nitrogen, killed either with silicon or aluminum. In the melts containing titanium, the interstitial atmospheres around dislocations are absent, and these materials do not show a yield point. The lower yield point becomes practically independent of grain size, so that the ky value in the Petch-Hall equation is very low. On the contrary, the yield strength of silicon and aluminum killed melts is markedly grain size dependent and the ky value is very high. After irradiation in the SORIN RSI swimming pool reactor with fast neutron fluences up to 1.4 × 1019 nvt (>1 Mev) the tensile properties of the different materials and the transition temperature of the fracture were determined. The irradiation-induced increase in yield strength of iron containing titanium, having before irradiation a yield point markedly lower than the other materials, is sufficiently large to bring to tensile properties not too different from the other materials; the yield strength is identically independent of grain size, at least in the small grain size region. The increases in the transition temperature for brittle fracture are about the same for the alloys containing titanium and for those killed with aluminum: a markedly larger shift was instead observed in the material killed with silicon. Some results on the recovery behavior of iron are also reported.
radiation effects, metals, nitrogen, iron, neutron radiation, interstitial impurities, impact strength, dislocations, microstructure
Researcher, Societá Ricerche Impianti Nucleari, Saluggia,
Headassociate professor solid state physics, Istituto Elettrotecnico G. FerrarisUniversity of Torino, Torino,
Rossi, F. S.
Head, Societá Ricerche Impianti Nucleari, Saluggia,
Division head, European Community for Nuclear Energy, Brussels,