Relation between fatigue crack initiation and structure in pearlitic steel

To clarify the relation between fatigue crack initiation and the crystal structure in pearlitic steel used for railroad rails, fatigue tests are performed, focusing on crack initiation. Then, the fracture surfaces are analysed using a scanning electron micro-scope (SEM). To observe the crystal structure, before the fatigue is performed, the specimen surface is etched chemically. The crystal structure of pearlitic steel, is comprised of "pearlite colonies" which have the same lamellar structure direction, and "pearlite blocks" which have the same ferrite crystal direction. A fatigue crack initiation region should be affected by the crystal structure; however, the relation between the crack initiation region and the crystal structure in pearlitic steel has not been clarified. From the fatigue test results, the fatigue crack of the pearlitic steel was initiated at a very early stage of the fatigue test. To determine the unit of fatigue crack initiation in pearlitic steel, the relation between the crack initiation region and crystal structure was clarified by using SEM analysis.