Abstract
Pulsating tensile fatigue tests were carried out, using CT specimens cut out in three different directions from a rolled steel having inclusions with a remarkable directionality, in spite of having slightly laminated structures. The crack growth rate in each directional specimen was measured by an optical microscope and the fracture surface was observed by a scanning electron microscope. The main results obtained are as follows. (1) the crack growth resistance is lowest in the case of SL specimens whose cracks propagate along the inclusions with directionality, but anisotropy of the crack growth rate is small in comparison with that of the fatigue limit. (2) The anisotropy of the crack propagation is clearly recognized also by observing the fracture surface in fatigue. (3) The effect of material strength on the crack growth rate is remarkable when the stress intensity factor range ΔK is large, while it is slight when ΔK is small.
