EFFECTS OF DRAWING STRAIN AND BLUING ON THE FATIGUE-STRENGTH OF EUTECTOID STEEL WIRES

The effects of bluing, associated with drawing strain, on the fatigue strength of eutectoid steel wires have been investigated. The fatigue limit increases by bluing and the increase is more significant with hi gher drawing strain. The peak in the fatigue limit with regard to the drawing strain in the wires, at a strain of 2.5, disappears after blui ng. On the other hand, in the ferritic steel wires investigated for co mparison, the fatigue limit gradually increases with the drawing strai n up to 7.7. Furthermore, no appreciable change in the fatigue limit d ue to bluing is found. Based on the results of hardness tests on fatig ue specimens with-and without-bluing, it is deduced that the decrease of the fatigue limit beyond the peak drawing strain in the eutectoid s teel wire can partly be attributed to insufficient locking of the high -density dislocations by solute atoms. The effect of relaxation of res idual stress during bluing is also briefly discussed.