Abstract
By the torsional fatigue testing machine for steel wires mentioned in the 1st report, we studied on the torsional fatigue limits of three steel wires with different carbon contents (0.6% and 0.8%) and reductions in cold drawing (86% and 72%). The diameters of these wires are all 1.7mm. And at the same time we inquired into the effect of the low temperature annealing in the range of 100-500°C for 20min after cold drawing on the torsional fatigue limits. The results obtained are as follows:
i) Steel wires with high carbon content and high reduction in cold drawing have high torsional fatigue limits.
ii) The torsional fatigue limit and the static strength are improved by the low temperature annealing after cold drawing. And the former becomes maximum in the annealing temperature within the range from 200°C to 400°C, but all of the latter at about 200°C.
iii) The low annealing temperatures at which the torsional fatigue limit and static strength become maximum are not always equal. The differences between these temperatures tend to become remarkable in steel wires with high carbon content and high reduction in cold drawing. This seems to be caused by the residual stress in the cold drawn steel wires.
iv) The ratios of the torsional fatigue limit τw to the tensile strength σB or the torsional strength τB in these wires were 0.13-0.17 or 0.17-0.22.
