Microstructure origin of strength and toughness of a premium rail steel

ISSN： 1059-9495

Source： Journal of Materials Engineering and Performance, Vol.10, Iss.3, 2001-06, pp. : 331-336

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Abstract

The mechanical properties, fracture toughness, fracture surface morphology, and failure mechanisms of different layers in a premium railhead were studied. Correlation between the mechanical properties and the failure mechanisms for each of the layers was made. It has been found that the microstructure and mechanical properties of the top layer are different from those of the inner layers, while the middle layer and the layer near the web demonstrated similar mechanical properties, microstructure, and fracture toughness. The top layer displayed 15% higher tensile strength than the other two layers. However, the strain to failure of the top layer, 11%, is only about 60% of that of the inner layers, 17.5%. The top layer has a fracture toughness, K _Ic, of 75 MPa m^1/2. This value for the inner layers is about 95 MPa m^1/2. Thus, the heat treatment decreases the ductility and fracture toughness of the top layer of the railhead. Transition from the brittlelike fracture mechanism of the top layer into a more ductile mechanism of the inner layers was also found.