Dry rolling-sliding wear of austempered cast iron

In the present investigation, the dry rolling-sliding wear of two austempered ductile irons (ADIs), characterized by different hardness values, was investigated. The tests were carried out using disks with 40 mm diameter and 10 mm height. The applied load was in the range between 50 and 500. N. Since the initial Hertzian pressures were quite large because of the line contact, a plasticity dominated wear with the formation of delamination was obtained. Therefore, the treatment cycle of some specimens was conducted with the aim of obtaining a mild wear during rolling-sliding through the formation of a surface oxide layer. As a comparison, the dry rolling-sliding wear of a gas nitrided steel was also investigated.The results show that the wear coefficients of the specimens with the oxide layer on their surface was actually mild. However, the specimens produced without such a layer displayed even lower wear coefficients. Although wear was by delamination, wear coefficients were still low because of the action of graphite, which was able to squeeze on the surface during sliding, thus reducing adhesional forces. In addition, a mechanically mixed layer formed on the sliding surfaces, and this provided an additional increase in the wear resistance. Because of this, the material with lower matrix hardness displayed a greater wear resistance. The wear resistance of the nitrided steel was found to be determined by the outer part of the compound layer, and it was found to be lower than that displayed by the two ADI. © 2011 Elsevier B.V.