Micro fracture investigations of white etching layers.

The fracture behavior of a white etching layer formed on the rail surface in pearlitic steels during the rail-wheel contact is investigated using indentation-based microcantilever fracture tests. The sample thickness is in the order of 5 μm. The local fracture toughness of the white etching layer, its neighboring brown etching layer, martensite and pearlite with similar chemical composition are determined and compared to ferritic steels. All samples show stable crack growth accompanied by significant plasticity at the crack tip. The toughnesses scale inversely with the microhardness. The white etching layer exhibits a toughness of 16.0 ± 1.2 MPa m1/2 which is in the same range as the fully martensitic steel. It is shown that the local fracture toughness can be roughly estimated based on the Vickers hardness of the white etching layer. Also, an estimation of a critical defect size in white etching layers which considerably furthers the understanding of crack initiation is made in this study. Furthermore, various criteria for analyzing the elasto plastic fracture toughness are compared. Unlabelled Image • The fracture toughness of WELs and comparable microstructures were obtained using elasto-plastic micro fracture experiments • The fracture toughness of WELs is comparable to martensite • The fracture toughness of WELs can be estimated from the hardness via a proposed empirical relation. • Various criteria for interpreting the J-integral at small scales are quantitatively compared and discussed. • We determined critical defect size in WELs. [ABSTRACT FROM AUTHOR]