The document discusses evaluating the fracture toughness of carbides in tool steels using nanoindentation techniques. It finds that Laugier's expression for calculating fracture toughness (KC) from indentation data is most appropriate when using a Berkovich indenter at low loads that generate short cracks under 10 microns. Applying this expression, the study determines KC values for various carbides in different tool steels, finding that vanadium-rich carbides exhibit higher toughness. Relating the hardness and toughness of carbides can guide the design of tool steels with optimized wear and fracture resistance through their microstructure.