Investigation shows that there is a preferred cobalt content for a given hardness of a cemented carbide insert when used in a bit which is drilling iron ore. Two parameters determine the hardness of a cemented carbide: cobalt percent and tungsten carbide grain size. By manipulating these two parameters, a number of cemented carbide materials can be made which have the same hardness. Three iron-ore drilling tests have been conducted where test bits contained materials having essentially the same hardness, but where the materials were varied through a range of cobalt content and tungsten carbide grain size. Graphs are presented which depict the effect on fracture resistance of varying the cobalt content-tungsten carbide grain size. In each test, one material showed superior fracture resistance. The test bits drilled iron ores such as hematite or taconite.

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