In this research work were analyzed the reasons for fracture of pin machined from 42CrMo44 steel. One pine build in TBU (Tread Brake Unit) of railway wagon breaking system was broken in exploratory condition. Reclamation from purchaser was sent to the producer concerning occurred fracture of pin. Producer sent request to the team of the Faculty of Technology and Metallurgy to perform investigations and to determine the reason of fracture (failure analysis). It was decided to perform the following investigations: visual inspection, determination of chemical composition, hardness measurement, metallographic investigations which include analysis of microstructure and quantitate determination of nonmetallic inclusions. For comparison of results, raw material for pin production i.e. solid bars φ50, and new none used bar from the same steel was investigated too. Performed investigations showed that the main reason for the fracture of pin is the quality of the raw material more concretely segregation of chemical elements and increased concentration of nonmetallic inclusions.