Abstract
To obtain the effect of cold rolling on fatigue strength, commercial 0.8% carbon eutectoid steel was cold-rolled to various degrees of reduction and then fatigued in bending at constant deflection. On the other hand, cold-rolled strips are always accompanied by residual stress, and the fatigue strength is much influenced by the residual stress on the surface of cold-rolled sheets. The residual stress on the surface of the sheet cold-rolled at each rolling rate was measured by the X-ray method (sin2 ψ method) which was corrected by Fourie Analysis. The intrinsic change of fatigue strength by cold rolling was obtained using the relation between fatigue strength and mean bias stress. As a result, the fatigue strength increases monotonously with the reduction rate, and the increasing rate of fatigue strength with the reduction rate in the earlier stage of cold rolling, if uncorrected by residual stress, is very large because of the large compressive residual stress.
As an example, the residual stress on the surface of a cold-rolled sheet changes neither by the cold rolling rate of at least more than 10% nor by the one-pass reduction in the range of 1.9%∼4.7%.
