Kinetics of strain aging in bake hardening ultra low carbon steel - a comparison with low carbon steel

The kinetics of the static strain aging process have been analyzed in a vac uum-degassed ultra low carbon bake hardenable (ULC BH) steel with a total c arbon content of 20 wt.ppm through measurement of the strength properties. The influence of prestrain and free interstitial carbon content has been st udied. The kinetic results were compared with those of a BU low carbon (LC) steel. In the derivation of the time exponent and the activation energy, o nly the first stage of aging was considered. It was observed that, at all p restrain levels and matrix solute carbon contents, the initial aging proces s in the ULC steel obeyed the t(2/3) kinetic law and the kinetics were not influenced by the changes in dislocation structure due to prestrain and the dissolved carbon content. In comparison, the aging process and the kinetic s in the LC steel were found to be significantly influenced by the amount o f prestrain. The presence of carbide particles in LC steels can modify the aging kinetics.