CRACK INITIATION IN PLAIN CARBON STEELS DURING STATIC TENSION AND FATIGUE

In this work, the effect of carbon content on static tensile and fatigue
crack initiation behaviour was investigated on four different types of carbon
steels with nearly equal ferrite grain sizes by the plastic replica method. Static
tests and fatigue tests had been performed using the universal testing machine
and the rotating bending fatigue testing machine, respectively. Fatigue tests
were mainly performed under the stress level larger than the fatigue limit of
each material by the same magnitude. Experimental results show that. for
tensile tests, the cracks of materials with low carbon content exist in the
boundaries beiween pearlite block and ferrite grain or in their neighborhood.
On the other hand, those of materials with medium carbon content cracks also
exist in pearlite. For fatigue tests, the carbon content of each material affects
the crack initiation behaviour under the same stress amplitude for four types of
carbon steels, comparing with that under the stress level larger than the fatigue
limit of each material by the same magnitude. In addition, the carbon content of
steel hardly affec~s the crack propagation behaviour .