Abstract
Upon statical bending, Charpy impact and repeated impact tests as measure of the brittleness of sintered hard alloys used for the rock bits, it was shown that the number of repetitions causing breakage under repeated impact tests was the best representation of the brittleness of the tips. It was also recognized that these values correlated closely to the boring length until breakage of the tips occurs in field tests. Applying the test standard, in which it was prescribed that there should be no breakage within 1,000 repetitions under 10 kg-cm impact energy in T.K. type repeated impact tester, we found almost no undesirable evidence in any rock bit tips, and we succeeded in selecting highly reliable tips, capable of boring hard rocks to more than 100 meters.
