EFFECTS OF OVERBASED ORGANIC METAL-SALTS ON LUBRICITY IN HOT-WORKING

A new method to present a lubricating composition which can effectivel y 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 m etal/metal contacts. The degree of seizure and coefficient of friction of mineral oil based organic metal salts,lithium grease based graphit e, conventional hot-rolling oil are estimated by disc-block type frict ion 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. Th e results obtained are as follows; (1) A lubricating composition inclu ded overbased metal sulfonates was effective for preventing seizure by action of a large quantity of calcium carbonate (average particle dia meter < 100 Angstrom) 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 i nto FeO . CaO on steels in rolling bite,and prevent roll oxide film fr om growing up.