Effect of Cold Work on the Precipitation of Copper from Alpha-Iron

Precipitation of copper in iron alloy containing 1 wt% copper was measured from the changes in electrical resistivity at liquid nitrogen temperature and in tensile strength. In the specimens quenched from 800°C, rapid precipitation was observed at 525°C when subjected to isochronal aging, in which the temperature interval and the time were taken as 50°C and 30 min, respectively. The activation energy for the precipitation is determined as 53±6 kcal per mol. Meanwhile, in the specimens cold-worked after quenching from 800°C, copper was precipitated in a considerable amount at about 250°C under the same conditions of isochronal aging. The activation energy for the precipitation is calculated as 32±1 kcal per mol. Excess vacancies introduced into specimens by cold-working are considered to be effective in the diffusion mechanism for the precipitation at about 250°C.