Influence of Surface Competition Between Lubricant Additives on the Defect Formation in Cold Rolled Steel

Black band defect often observed after cold rolling of steel is a surface defect which negatively impacts the cold rolling process as well as downstream coating process. This leads to rejection or downgradation of coils. Modern day surface profilometry helps in understanding the nature of surface defect. Not much literature reports or detailed work is available related to the cause behind this defect formation. Phosphorous-based anti-wear additives are known to play a critical role in the formation of tribofilm. With aging of the lubricant, the formation of tribofilm gets affected owing to the in situ formation of fatty acids and competing tribochemical reactions. The competing reaction results in easier removal of tribofilms accompanied with friction, heat generation resulting in band formation. This paper presents detailed analysis followed by novel laboratory simulation of the defect formation. Tribological studies coupled with advanced instrumental techniques like GDOES, Raman Spectroscopy and FTIR have been employed to understand the nature of defect and role of cold rolling oil leading to the defect formation.