| 摘要 |
A process for surface hardening a ferrous article such as an aircraft engine rocker lever shaft includes the steps of creating a nitrocarburized oxide layer atop the ferrous core, and subsequently creating a nitrogen enriched case between the oxide layer and the ferrous core. The article is exposed at a first elevated temperature to a mixture of an inert carrier gas, ammonia, carbon dioxide and sulfur dioxide, and thereafter exposed to the carrier gas and ammonia at a second elevated temperature higher than the first temperature. The article formed by the process has a ferrous core covered by a case of nitrogen enriched, institially hardened steel over the core, and a complex nitrocarburized oxide layer atop the case. The complex nitrocarburized oxide layer includes a lower portion comparable to a conventional epsilon nitride or white layer, and an upper porous oxide zone. The upper porous oxide zone is preferably infused with an extreme pressure oil or a liquid polytetrafluoride material. The case is generally 0.010 to 0.035 inches thick, while the complex oxide layer is about 0.0008 to 0.0015 inches thick. The surface hardened articles so formed possess substantially superior resistance to wear, galling, case crushing and surface fatigue, as compared to conventionally hardened articles. |
