Efeito da pressão de compactação e do tamanho do pó de ferro na abrasão do ferro sinterizado oxidado a vapor

Abstract

Steam oxidized sintered iron-based materials have been, and continue to be used for toad bearing parts in sliding contacts. Although the permanence of an oxide layer on the external surface is reported to be the main factor affecting tribologicai 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 work, 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 Hdganas) of different sizes (<65pm, 65 - 90pm, 90 - 125pm, > 125pm). They were compacted at four different pressures (300,400, 500 and 600 MPa), sintered for 30 min at 1120°C and then subjected to continuous steam treatments at 540 °C for 2h. 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 (Al203 and Si02) and one endogenous abrasives (Fe203) 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. 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.