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Development of high performance lubricants for hot forging of steel has been strongly needed to expand die life and to improve working environment at factories. Thereupon, graphite lubricants have been altered into non-graphite lubricants in hot forging of simple parts. However, these non-graphite lubricants have insufficient property. In this paper, low-speed ring compression test was proposed to estimate the frictional property of lubricants for hot forging of steel. It was found that each lubricant has critical temperature less than 450 to reduce the friction between the dies and the 1000 billet.

A backward can extrusion test provides severe tribological conditions because high pressure, high temperature, and large surface expansion ratio affect the lubricant. During the forward stroke these conditions intensify with increasing cup depth of the extruded workpiece; additionally, the back-stroke force during retraction of the punch rises to a significant level under a poor-lubricated condition. This study estimates the coefficient of friction μp between punch and workpiece during the back-stroke by combining experiments using conventional soap-phosphate coated steel and numerical analysis by FEM. The values of μp were estimated to be 0.09 and 0.03 in case of small and large workpiece depth, respectively. Friction decreased with elevating temperature.

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