Effect of dislocation density on the low temperature aging behavior of an ultra low carbon bake hardening steel

Strain aging was studied in an ultra low carbon (ULC) steel with a total ca rbon content of 20 ppm (wt.%) in order to identify the process stages and m echanism of bake hardening in this type of steel. The effects of dislocatio n density, varied by means of uniaxial tensile prestraining (1-10%) on the aging kinetics were investigated within an aging temperature range of 50-17 0 degrees C. The aging was evaluated by means of strength measurements and the determination of interstitial carbon content after aging using a piezoe lectric composite oscillator operating at 40 kHz, The interaction between i nterstitial carbon and dislocations was examined through amplitude dependen t internal friction measurements. The influence of dislocation density on t he aging behavior have been discussed with reference to the kinetics and me chanism of the aging process. (C) 2000 Elsevier Science S.A. All rights res erved.