STRAIN AGEING AND THE FATIGUE LIMIT IN CARBON STEEL

Abstract

Abstract The fatigue phenomenon of mild steel is characterized by the existence of a fatigue limit and coaxing effects. Although many studies have been made on strain ageing due to interstitial solute atoms of carbon and nitrogen, the effect of strain ageing on the fatigue limit is not yet fully understood. The objective of this work is to clarify the effect of strain ageing on the fatigue limit. Experiments were undertaken from the view point that fatigue is a competitive process of two mechanisms of damage and strengthening of the material. Two techniques were applied for this purpose. One was the measurement of the change in solute contents of C and N atoms, and the other the reversion of the Cottrell atmosphere. The experimental results recognized that strain ageing occurred in the fatigue process and that by removing the strain ageing effect, specimens could fail below the fatigue limit. The fatigue limit could be increased above the original value by suppressing dislocation multiplication during fatigue. It was also observed that, as the time for strain ageing increased at higher temperatures, the knee of the S–N curve shifted to smaller number of cycles. Copyright © 1979, Wiley Blackwell. All rights reserved