A hot work tool wear test and friction coefficient determinations have been used to investigate how TiN- and TiAlN-coated tools start to fail under simulated hot-working conditions. The coatings were deposited by triode ion plating onto H13 steel discs representing the tool. In the test an induction-heated steel bar representing the workpiece reciprocates perpendicularly to the rotating disc face. The wear track was studied microscopically to detect incipient wear. It was found that the damage to the coating is initiated by cracking along lines lying at right angles to the direction of the wear track. Cracking leads to micropickup along the cracks and finally to large friction weldings. Frictional force and thermal shocks caused by workpiece-tool contact result in tension stresses and contribute to the onset of cracking.