On the chemical nature of boundary lubrication of stainless steel by chlorine- and sulfur-containing EP-additives

The nature of the extreme pressure CEP) effect of the dialkylpolysulfides a nd chlorinated paraffins during the ironing of stainless steel AISI 304 has been studied. A strip reduction test was used in combination with differen tial thermal analysis (DTA), profilometry, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy analysis (AES). Strip reduction tests, in which chlorinated paraffin and dialkyl sulfide we re compared as EP-additives, have shown significantly stronger EP-effect of the chlorine containing lubricant, than for the sulfur containing lubrican t. DTA analysis of the Me-powder (where Me = iron, chromium or nickel)-dial kylpolysulfide (or chlorinated paraffin) mixtures have shown that dialkylpo lysulfide was chemically active with iron and nickel (the highest activity was with nickel). Chromium was practically nonactive with dialkylpolysulfid e. Chlorinated paraffin was equally active with iron, chromium and nickel. The better lubrication performance demonstrated by chlorinated paraffin com pared to dialkylpolysulfides was attributed to the chemical activity of the chlorinated paraffin with all the main components of stainless steel. The depth profiles of the stainless steel strips were examined before and a fter strip reduction by use of AES sputter profiling. Results imply that th e chlorine containing lubricant enforces the formation of a thick oxide lay er. (C) 2000 Elsevier Science S.A. All rights reserved.