Fracture toughness of carbides in tool steels evaluated by nanoindentation

In this study, the hardness and fracture toughness of different primary carbides present in tool steels have been evaluated by nanoindentation. Toughness was evaluated by the indentation method using Laugier's equation, after experimentally assessing its applicability. The results obtained allow different types of carbides to be discerned, in terms of hardness and toughness, which ranges from 2.2 to 3.7 MPa m(1/2). It has been found that M7C3 carbides exhibit a marked fracture resistance anisotropy, which is lower in the direction parallel to its larger edge. This anisotropy is related to the crystalline texture. The relationship between hardness and toughness of the analysed carbides can be used as a guideline for the selection of the most appropriate type of carbide that the microstructure should contain in order to optimize the wear behaviour and the fracture resistance of a tool steel. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.