Effects of Overbased Organic Metal Salts on Lubricity in Hot Working

Abstract

A new method to present a lubricating composition which can effectively prevent seizure during hot rolling of stainless steels is proposed: both "the Principles of Hard and Soft Acids and Bases" for improving chemisorption force and "the super fine particles" for decreasing metal/metal contacts. The degree of seizure and coefficient of friction of mineral oil based organic metal salts, lithium grease based graphite, conventional hot-rolling oil are estimated by disc-block type friction test at elevated temperature. Effects of lubricants on roll oxide film are investigated by model hot rolling mill. Chemical reactivity of lubricants for a fresh and oxide surface is investigated by XPS.
The results obtained are as follows; (1) A lubricating composition included overbased metal sulfonates was effective for preventing seizure by action of a large quantity of calcium carbonate (average particle diameter < 100 Å) in hot metalworking. (2) Calcium sulfonates have the highest lubricity among the alkaline earth salts of the sulfonic acid having the same base number and a higher base number is better. (3) It is made clear that the overbased Calcium sulfonates change FeO into FeO·Ca0 on steels in rolling bite, and prevent roll oxide film from growing up.