The Formation Of Low Carbon Bake Hardening Steel Cottrell Atmosphere And Impact On BH Value

For the low carbon bake hardening steel, BH values of different aging temperatures and aging time and internal friction spectrums under the corresponding aging process were measured. The effect of the changing carbon content of solid solution and Cottrell atmosphere formation on BH value were analyzed.Strengthening mechanism and aging kinetics equation of low-carbon steel were researched. The main results of the research were as follows:(1) The experimental steel by 2% pre-deformation, aging at 170 ℃10min to10000 min,with the increase of the aging time, the BH value increased gradually, the yield point elongation lead gradually increased. When aging time was 5000 min, it started to decrease. As the aging time prolonged, Snoek peak height gradually decreased, SKK peak gradually increased. When aging time was to 5000 min, Snoek peak and SKK peak both decreased. Aging 1000 min, Cottrell atmosphere reached saturation, and to extend the aging time, strengthening mechanisms were Cottrell atmosphere and carbide precipitation interaction.(2) The experimental steel by 2% pre-deformation, then aging at 250 ℃, with extension of aging time, BH value gradually reduced. Snoek peak height first decreased, and then gradually increased. When time was to 5000 min, it began to decrease. SKK peak gradually increased with extension of aging time, but at 5000 min,SKK peak began to decrease. The grain boundary internal friction peaks at 250℃aging were lower than those at 170℃ aging. At 250℃, aging strengthening mechanisms were both Cottrell atmosphere and precipitation strengthening, and the precipitation strengthening was the main strengthening mechanism.(3) With the increase of the pre-deformation amount, the BH value reduced.Verification by the formula: With the increasing of Cottrell atmosphere density, BH increased; With the number of Cottrell atmosphere increased, BH value also increased.Using Harper model, at 50 ℃ and 100 ℃ aging, the kinetic formula could be expressed as 101-=-ktw)()1ln(; At 170 ℃ aging, the kinetic formula was51-=-ktw)()1ln(. The pre-deformation amount had no effect on the kinetic formula,but the aging temperature had an effect on the kinetic formula. Using Hartley model model, the kinetic formula could be expressed as 101max=ktDDss. The pre-deformation amount and aging temperatures had no effect on the kinetic formula. Therefore, for the low carbon bake hardening steel in this paper, Hartley model was more suitable.