Effect of martensite content on friction and oxidative wear behavior of 0.42 Pct carbon dual-phase steel

In order to explore the tribological potential of the dual-phase (DP) steel as a wear-resistant material, the friction and wear characteristics have been investigated for this steel with varying amounts of martensite from 42 to 72 vol pct, developed by varying holding time at the intercritical annealing temperature of 740 °C. Dry sliding wear tests have been conducted on DP steels containing 0.42 wt pct carbon using a pin-on-disk machine under different normal loads of 14.7, 19.6, 24.5, 29.4, and 34.3 N and at a constant sliding speed of 1.15 m/s. Weight loss has been measured at different time intervals on the same specimen. The variation of cumulative volume loss with sliding distance has been represented by two linear segments signifying the run-in and the steady state of wear. The mechanism of wear is primarily oxidative in nature, which has been confirmed by X-ray diffraction patterns of the wear debris generated during sliding. The wear rate varies linearly with load in both the run-in and the steady state. The wear rate decreases linearly with increasing volume fraction of martensite in DP steels reflecting the effect of hardness imparted by the increasing amount of martensite, which is a hard and load bearing phase. The average coefficient of friction also decreases linearly with increasing load as well as with increasing martensite volume fraction. In the run-in stage, the wear coefficient does not change significantly between DP1 and DP2 steels containing 42 and 51 vol pct martensite, respectively, but decreases sharply as one moves from DP2 to DP4 containing, respectively, 51 and 72 vol pct martensite. But in the steady state, the wear coefficient decreases almost linearly with increasing volume fraction of the martensite. The decrease in wear coefficient may be attributed to the decreasing wear rate dominating over the decrease in real area of contact due to increasing hardness.