The Effect of Tensile Prestrain on the Fatigue Strength of Strength-Anisotropic Rolled Steel

Abstract

Rotating bending fatigue tests were carried out on the specimens cut out of a rolled steel in the rolling and thickness directions which had been subjected to a tensile prestrain. The fatigue processes were observed by the metallurgical microscope. The main results obtained are as follows: 1) When the thickness directional specimens are subjected to a tensile prestrain, inclusions are separated from the material, while the fatigue limit increases. 2) The fatigue limit of the thickness directional specimen is determined, irrespective of the percentage of the prestrain, by the propagating limit conditions of non-propagating cracks occurring from inclusions. And in rolling directional specimens, inclusions have no relation to the crack initiation in all cases of the prestrain. 3) In both rolling and thickness directional specimens, the portions where the slip bands concentratedly initiate in the fatigue test are the ones where the slip bands initiate under the prestrain.