The role of sublayer in determining the load bearing capacity of nitrocarburised pure iron

Plasma austenitic nitrocarburising as well as plasma ferritic nitrocarburising treatments of pure iron have been carried out in a modified dc plasma unit at 700 degrees C with a gas mixture of nitrogen, hydrogen and organic vapour as the carbon-nitrogen media supplier. The composition, phase structure, microstructure and hardness of the plasma nitrocarburised surface were characterised by a number of materials analytical techniques. The load bearing capacities of ferritic nitrocarburised and austenitic carburised samples were evaluated using a Falex tribometer, and the effect of the sublayer in determining the load bearing capacity of plasma nitrocarburised material was investigated. The experimental results show that the load bearing capacity of plasma nitrocarburised pure iron is mainly determined by the hardness of the sublayer. The load bearing capacity of plasma nitrocarburised pure iron increases in the order of (i) plasma ferritic nitrocarburised, (ii) plasma austenitic nitrocarburised and slow cooled, and (iii) plasma austenitic nitrocarburised, quenched and subzero treated. Based on the experimental results, the role of the sublayer in determining the load bearing capacity of plasma nitrocarburised material is discussed.