Fatigue in C/Si/Mn steels.

British Railways is a major material user. It has high maintenance costs due partly to the premature withdrawal of components from service caused by metal fatigue. The main interest in fatigue, in terms of greater component efficiency, lies in the successful prediction of life for different, variable amplitude loading conditions. This requires extensive knowledge of both the service load environment and the response of metals to variable cyclic loads. This thesis presents the results of an investigation into the cyclic behaviour of ferrite-pearlite, C/Si/Mn steels. An analytical, computer based method for predicting fatigue life, forms the basis of the approach used. The materials data required in the analysis is obtained for a series of steels containing a wide range of compositions and microstructures. This data is assessed in terms of more easily obtained mechanical properties and also in terms of the metallurgical variables. Certain assumptions in the model regarding material behaviour are also evaluated using the data. Finally, the data is used to assess the importance of material changes in variable amplitude fatigue situations.Observations of surface fatigue damage and fracture surfaces have also been carried out. This work is used to develop a theory for the formation and development of cracks in ferrite-pearlite structures.To conclude, the results of the various investigations are used to consider the future development of fatigue resistant materials.