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The aim of this thesis work was to design and evaluate a wear test method for cemented carbides inserts used in rotary drilling. An appropriate in-house wear test method would provide a better understanding of the wear mechanisms limiting tool life in real drilling. The test method should be easy to use and be able to distinguish between wear of insert materials with different microstructure and properties. The literature study showed few published articles about wear tests and mechanisms concerning rotary drill bit inserts. These methods included two standard wear tests; ASTM G65 and ASTM B611. Furthermore, a modified ASTM G65 test was found as well as an impact-abrasion test. In this work the modified ASTM G65 test, using a rock counter surface, was evaluated in order to understand if the method would mimic the wear of cemented carbides used in rotary drilling. The test method was further developed and showed high repeatability. Measured weight losses showed that the test could distinguish between two common rotary grade materials with a small difference in hardness but with different microstructures. The wear of the tested materials was analyzed with scanning electron microscopy and compared with rotary drill bit inserts collected from the field. The modified test method proved able to produce wear by mechanisms very similar to those found on field worn inserts. Identified wear mechanisms included cracking, fragmentation and spalling of WC grains as well as embedded fragments of WC grains on the surface. In addition, the binder phase was removed and adhered material from the counter surface was detected.

This thesis work sought to find a tribological testing method suitable for cementedcarbide drill bit inserts used when drilling rock. A review of the literature publishedon the matter showed that there are quite a few test methods developed for wearstudies with cemented carbides, but most of them were not designed for the rockdrilling industry. Published studies performed with the found methods and articleswith analyzed field tests have been studied. It is generally agreed upon that the stepsof wear is that the binder disappears first, followed by removal of carbide grains. Themechanisms of binder phase and carbide grain removal is somewhat debated, butalmost every study observes fracture of the carbide grains. The wear test created inthis thesis was shown to give wear linear with time, but not with load. The newmethod was shown to be capable of distinguishing between different cementedcarbides worn in three body abrasion against different rocks. Analysis of the wornsamples shows that there are similarities with bit inserts worn in field testing. Many ofthe observations made during the analysis are also similar to observations inliterature.

This thesis work is performed at Sandvik Mining Rock Tools, a world leading supplier of rock drilling tools. The work is part of developing a new tribological wear test method for cemented carbide drill bit inserts. The test method has earlier been judged successful in mimicking the rotary-percussive rock drilling process because it gives the same wear mechanisms as have been observed for inserts used in rock drilling. During testing the cemented carbide drill bit insert is pressed against a moving rock surface while water and particles are added to the contact area. The particles are present to simulate the rock crushings formed during drilling. They are believed to cause abrasive wear of the inserts. In this work the effect of load, particle material and particle size are studied. When adding silica particles, which are softer than the cemented carbide material, no correlation is obtained between wear rate and load or particle size. Cracking of WC grains, added rock material and removal of pieces of carbide material are seen at the worn sample surfaces. These observations are similar to observations described in other works about wear of cemented carbide. Adding alumina particles, which are harder than the sample material, gives high wear rate and ground/striped sample surfaces. The wear rate increases with alumina particle size.