Precipitation and irradiation hardening in iron

Precipitation of carbon from α-iron during irradiation and thermal ageing has been studied using thin film electron transmission microscopy. During irradiation at 100°c precipitates formed with a density of 2 × 1014 cm−3 and saturated at 400 Å diameter after 72 hours in a flux of 1·5 × 1011 neutron cm−3 sec−1 > 1 MeV. The precipitates were in the form of plates parallel to {100} and occurred individually in the matrix and in rows on dislocation lines. Thermal ageing at 100°c produced dusters of plates with a density of 3 × 1013 cm−3 and rows of plates on dislocation lines. At higher ageing temperatures the plate-like precipitates were replaced by larger dendritic particles at 200°c and needle-shape particles at 250°c with a density of 3 × 1013 cm−3. The defects produced during irradiation, which are responsible for irradiation hardening, were not detected. Tensile experiments showed that the hardening was most pronounced when precipitation did not occur.