Internal Friction Study of Aging Hardening and Kinetics in Low Carbon Steel

The low carbon steel with 2% pre-strained had the strain aging treatment in different baking time at 170 C. The stress-strain curves, bake hardening (BH) value and internal friction-temperature spectrum of tested steels were studied by tensile test and internal friction. The Harper aging kinetic equation respectively using the parameters of BH value, yield point elongation (YPE) or Snoek-Ke-Koster (SKK) peak height was established. The results show that with the increase of aging time, the yield point elongation and BH value of tested steel increases, and then the stress-strain curve of the steel become from continuous yield to discontinuous yield. In the internal friction-temperature curve, the Snoek peak height decreases, the SKK peak height continuously increases, and peak temperature changes slightly. It indicates that the primary mechanism of age hardening is Cottrell atmosphere hardening. The time index n in the Harper aging kinetic equation fitted by the BH value, YPE and SKK peak height were 0.53, 0.59 and 0.59, respectively. The linear relationship of BH value and SKK peak is BH=17119"11sKK-33. (C) 2017 The Authors. Published by Elsevier Ltd.