This paper discusses the transition diagram for the wear mechanisms of cast iron pairs lubricated in sliding contact. Experiments simulating wear events have been conducted with a cylinder-on-disk apparatus using a fully flooded condition. As the load was stepwise increased, the modes of lubrication and the status of wear were determined by the steep increase in frictional coefficient and wear rate. The transition diagram of the wear mechanisms of lubricated iron/iron sliding-rubbing pairs consists of four regions. Worn surfaces and surface layers in the transition from mild to severe wear are examined. The results show that the transition is characterized mainly by the appearance of adhesion. The load-bearing capacity of the materials is related to the energy consumption in surface layers affected by the wear process.