The fatigue threshold, surface condition and fatigue limit of steel wire

To test the hypothesis that fatigue cracks in drawn, pearlitic steel wire propagate from pre-existing surface defects which can be treated as cracks, the fatigue limits of five different wires have been statistically determined. The fatigue thresholds were measured using a new AC potential drop method and the initial defect depths then calculated using the equation a_o=1π(ΔK_th/2σ_e)² and compared with observed values.

For higher strength steel wires (σ_u>1800 MPa) the agreement was very good; for the lower strength steel wire (σ_u=1469 MPa), however, the observed values were smaller than the calculated ones. The reasons for this discrepancy are discussed. A quantitative model is developed from the hypothesis and the influence of residual tensile stresses, decarburization and polishing on the fatigue limit of drawn steel wire is assessed.