Effects of a stepwise change in load on the subsequent friction and wear characteristics of carbon steel under dry sliding

Machines and components in operation are usually subjected to varying loads. However, wear tests of metals have usually been conducted under constant loads since early times in wear study. In this study, in order to investigate the effects of a change in load on the transition from mild to severe or quasi-mild wear, pin-on-disk type wear tests of carbon steel in contact with itself were conducted in moist air under dry sliding. During wear testing, the load was changed in a step-wise manner just one time from low to high levels. A longer sliding distance under mild wear conditions at low load in the first stage produces a more flattened and oxidized sliding surface having high wear resistance. In other words, a quasi-mild wear regime similar to mild wear with low rate occurred even at high loads in the second stage. The critical sliding distance in the first stage necessary for the transition to quasi-mild wear in the second stage is given by an empirical formula. The proposed formula indicates that the critical sliding distance decreases with increasing load in the first stage and decreasing load in the second stage. In conclusion, the quasi-mild wear can be attained under shorter sliding distance at higher loads in the first stage.