Abstract
The fatigue process of steel is characterized by the existence of fatigue limit and coaxing effect. Many researches have been made from the viewpoint of strain ageing brought about by interstitial solute atoms of carbon and nitrogen. The effect of strain ageing on fatigue limit, however, is not fully understood.
This experiment is undertaken from the viewpoint that fatigue is a competitive process of two mechanisms of damage and strengthening of the material. Two techniques are applied for this purpose. The change in the solute content of C and N atoms is measured by internal friction. Artificial ageing and reversion are applied in order to change the density of Cottrell atmosphere at dislocations.
The experimental results are as follows:
The solute atomic content in Ferrite decreases as the fatigue process advances. The material is hardened by strain ageing to the extent of 1∼1/2 times of strain hardening. The fatigue limit is explained by the competitive relation between active slip systems and strain ageing.
