The aim of the present research is to determine the initiation and propagation of cracks and its geometric specifications. Metallurgical factors, especially the non-metallic inclusions have a significant impact on the fatigue life of railways. Since all non-metallic inclusions in a measure of steel alloy is not dangerous, determining how and which one of them affects the fatigue process of the rails is of the present studies\\\' concern. Afterwards, the results of the research on fracture surface of fatigue specimens will be presented. Numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the specimen. For this purpose, the fatigue crack growth and hardness tests were carried out and have been checked by fractography studies on fractured specimens. The hardness of the specimens was measured in different points by using Rockwell microhardness experiment. Afterwards, a three-dimensional boundary element method is used for fatigue crack growth under stress field. The modified Paris model is used to estimate fatigue crack growth rates. Finally, threedimensional boundary element analysis results obtained show good agreement with those achieved in experimental tests.

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