Anisotropy of Low-Cycle Torsional and Push-Pull Fatigue in a Rolled Steel

Abstract

Low-cycle torsional and push-pull fatigue tests were carried out, using the specimens cut out of a rolled steel in the rolling and thickness directions and the fatigue processes were observed by the metallurgical microscope. The main results obtained are as follows: 1) In low-cycle torsional fatigue, the anisotropy of the fatigue strength between the rolling direction and the thickness direction is hardly observed as well as in high-cycle torsional fatigue. However, the inclusions in both rolling and thick directional specimens contribute to the crack initiation. 2) In low-cycle push-pull fatigue, a remarkable anisotropy of the fatigue strength between the rolling direction and the thickness direction is observed. This is due to the fact that the fatigue crack initiates from slip bands or grain boundaries in rolling directional specimens, while it initiates from the inclusions in thickness directional specimens.