THE PROPERTIES OF IRON CONTAINING A FINE OXIDE DISPERSION

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Abstract
Gel precipitation has been used to produce fine dispersions of thoria in iron. The process involves coprecipitation of hydroxides followed by a hydrogen reduction. Iron containing up to 7·65 vol.-% thoria was prepared with particle sizes in two ranges averaging 6 and 110 nm in diameter. The dispersion, stable up to at least 1300°C, raised the tensile and yield strengths by 80% compared with the iron made in the same way while retaining an acceptable level of ductility at ambient temperature and below. Impact testing showed that the presence of thoria did not have an adverse effect on the ductile-brittle transition temperature for thoria contents up to 4·55 wt.-%. It was not possible to estimate the strengthening due to the dispersions from the models of Orowan bowing of dislocations between particles because of the presence of two size ranges of particles in these alloys. The thoria dispersions did not raise the primary recrystallization temperature of the iron but were extremely effective in restricting secondary recrystallization. Grain sizes of <25μm were obtained after 15h at temperatures up to 1400°C. The thoria-containing alloys did not work harden more rapidly than the iron and with thoria contents up to 3 wt.-% could be readily cold worked.