鋼線の疲労に関する研究 (第2報)

Abstract

This investigation was planned for researching the effect of the total reduction by drawing and the low temperature annealing upon the distribution of longitudinal residual stress of 0.65%C steel wire, drawn at various reductions from 60% to 90%, with subsequent annealing in the range 150°C to 400°C. The diameter of all these wires was 1.3mm.For the measurement of the longitudinal residual stresses existing in these small wires, present writers adopted the dissolving method by acid, that is, the outer layers of the wire were successively dissolved off by 10% NHO3 and at each time the change of the gauge length was measured by the micro-comparator. And then that distribution of longitudinal residual stress was calculated by Heyn's formula.The results obtained were as follows:All wires tested had the similar distribution of longitudinal residual stress, that is tension in outer part and compression in inner part and the maximum tensile stress existed near the surface. For both wires as-drawn and annealed at 200°C or 300°C, the maximum tensile residual stress increased with total reduction by drawing up to 85%, and beyond this reduction it decreased. The release of residual stress by low temperature annealing was remarkable in case of over 300°C.From the fatigue limits of these wires reported in 1st report, the fatigue limits of these wires, on the assumption that there were no residual stresses, were calculated with the maximum tensile residual stresses measured in this investigation. As the result of this calculation, it was clarified that the maximum value of decreasing of the fatigue limit under rotating bending affected by the longitudinal tensile residual stress was found in the 85% reduced wire.