Abrasive wear of steam-treated sintered iron

Steam oxidized sintered iron-based materials have been, and continue to be used for load bearing parts in sliding contacts. Although the permanence of an oxide layer on the external surface is reported to be the main factor affecting tribological behaviour, in industrial practice as well as in laboratory tests abrasive wear is reported to play an important role in the final stage of the process. The removal of the superficial oxide layer, its fragmentation and transfer to the counter-body associated with metallic debris generation, induces the formation of hard debris particles acting as abrasives on the tribological system. In this paper, abrasive wear of steam-treated sintered iron is analysed by means of micro-abrasion tests. Sixteen specimens were produced from atomised iron powders (Ancor Steel 1000B Hoganas) of different sizes (<65, 65-90, 90-125, >125 mum). They were compacted at four different pressures (300, 400, 500 and 600 MPa), sintered for 30 min at 1120degreesC and then subjected to continuous steam treatments at 540degreesC for 2 h. The micro-abrasion tests were conducted under constant load and speed conditions while special emphasis was given to the nature of the abrasive; two exogenous (Al2O3 and SiO2) and one endogenous abrasive (Fe2O3) were used. The results show that the abrasion resistance is strongly influenced by the processing parameters, the lowest wear coefficients were obtained by using the highest compaction pressures and the smallest powder grade. The pore size is the main micro-structural parameter affecting the abrasive resistance. For all abrasives, interrupted tests showed that the small pores are completely filled by abrasive particles in the initial stage of the tests while the biggest ones remains open until the completion of the tests. Wear coefficients were strongly influenced (up to 10 times) by the abrasive nature. Scanning electron microscopy analysis showed that the abrasive wear mechanisms were determined by the abrasive particle features. (C) 2004 Elsevier B.V. All rights reserved.