A rotary drill bit comprising a roller cutter (13) rotatably carried over a bearing system, which comprises a friction bearing (14). For purposes of ensuring sufficient hardness of the cooperating friction surfaces and lubrication thereof and optimizing cutting ability and fatigue resistance the bearing surface (28) of the roller cutter (13) is surface-hardened by means of a thermal hardening method and provided with a solid lubricant (27), and the bearing surface (29) of the bearing pin (12) is provided with a wear resistant deposit having higher wearability than the surface-hardened bearing surface.