Nucleation and growth kinetics in high strength low carbon ferrous alloys

Nucleation and growth kinetics, and age hardening behavior in high strength, low carbon ferrous alloy containing 1.2 wt% copper and a model alloy, Fe–1.2%Cu, have been studied with and without the presence of carbides. It is well known that after austenization and quenching, Cu is retained in solid solution. During subsequent aging, Cu initially appears as a coherent nanometer size spherical precipitates. These precipitates, difficult to detect by conventional transmission electron microscopy (TEM), have been evaluated by small angle neutron scattering (SANS) measurements. Longer aging transforms the Cu precipitates into incoherent particles which are easily detected by conventional TEM. A combination of techniques such as TEM, SANS, and hardness measurements have been used to study nucleation and growth kinetics of copper in both alloy systems. Direct measurement from TEM micrographs and integral transform of the SANS data were used to calculate the size distribution for a variety of aging conditions.