Dry sliding friction and wear in plain carbon dual phase steel

In view of the potential of plain carbon dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite islands embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plain carbon normalized (N) steel that has the same composition of 0.14 wt pet carbon. Dry sliding wear tests have been carried out using a pin-on-disk wear testing machine at normal loads of 14.7, 24.5, and 34.3 N and at a constant sliding velocity of 1.15 m/s. Weight loss in the samples has been measured over time on the same specimen, and the variation of cumulative wear lass with sliding distance has been described by two linear segments, for both the DP and the N steel. At these loads, the mechanism of wear is primarily oxidative, although subsurface cracking and delamination wear could also be observed in a few places. The second linear segment could result from a dynamic steady state wear of the transfer layer of compacted oxide wear debris on the sliding surfaces. The wear rate calculated on the basis of the first linear segment varies linearly with normal load, which is indicative of Archard's law, and it is significantly lower for the DP steel than for the N steel. The wear rate calculated on the basis of the second linear segment, however, varies with load linearly for the DP steel but nonlinearly in the N steel. In the first linear segment, the wear coefficient is about 0.39 x 10(-4) for the DP steel and is 0.40 x 10(-4) for the N steel. Higher hardness and, consequently, a lower real area of contact in the DP steel at all the loads have compensated for the lower wear rates, and have resulted in a wear coefficient similar to that in the N steel. The steady state wear coefficient from the second linear segment is 0.29 x 10(-4) for the DP steel at all loads; for the N steel, these are 0.21 x 10(-4) and 0.64 x 10(-4), respectively, for lower and higher loads.