Development of chloride-free oil with sulfur-based EP additive for cold forming of stainless steel

Abstract

Galling and wear have been a tribology problem in sheet metal forming of stainless steel. Although lubrication oil with chlorinated extreme pressure (EP) additives have been used, environmental and safety issues have demanded not to use chlorinated EP additives. For developing chloride-free oil for cold ironing of stainless steels, some commercial sulfur-based EP additives were evaluated by a cup internal ironing test. Moreover, the superior sulfur-based EP additive was combined with calcium- and zinc-base type additives in order to improve anti-galling performance. The mixture oil, as shown the high performance in the cup internal ironing test, successively passed a 10,000 shots practical process with severe ironing of stainless steel. After the 10,000 shots, it was found that no galling was observed on these 10,000 products. Based on the X-ray photoelectron spectroscopy (XPS) results, sulfide and calcium carbonate were formed on the surface of the products. This lubricating film seems to prevent galling in the practical process. The developed oil is an example of a chloride-free oil to replace the conventional chloride-containing oil.