Scuffing Behavior of 4140 Alloy Steel and Ductile Cast Iron

Scuffing is a failure mechanism which can occur in various engineering components, such as engine cylinder kits, gears and cam/followers. In this research, the scuffing behavior of 4140 steel and ductile iron was investigated and compared through ball-on-disk scuffing tests. A step load of 22.2 N every two minutes was applied with a light mineral oil as lubricant to determine the scuffing load. Both materials were heat treated to various hardness and tests were conducted to compare the scuffing behavior of the materials when the tempered hardness of each material was the same. Ductile iron was found to have a consistently high scuffing resistance before tempering and at tempering temperatures lower than 427°C (HRC ≻45). Above 427°C the scuffing resistance decreases. 4140 steel was found to have low scuffing resistance at low tempering temperatures, but as the tempering temperature increases, the scuffing resistance increased. Ductile iron and 4140 steel had the same scuffing resistance at a tempering temperature of about 538°C (ductile iron HRC 35-36; 4140 steel HRC 40). The scuffed specimens were studied using optical and scanning electron microscopy to determine the scuffing mechanisms and scuffing results were analyzed based on material microstructure and hardness.