High-speed steel (HSS) materials are universally used as work rolls for the hot rolling of stainless steels. Their use has increased the output of the rolling mill and decreased roll material consumption and grinding. Sticking defects often occur, however, during the hot rolling process. In this article, extreme pressure (EP) additives were dropped on the HSS samples at high temperature. Zinc dialkyl dithiophosphate (ZDDP) was chosen as the most effective EP additive by scratch tests on the HSS samples. In order to determine the optimum proportion of ZDDP in the lubricant, two reduction rates were tested on a Hille 100 experimental rolling mill by hot rolling ferritic stainless steel 445J1M at five different concentrations of ZDDP. The mechanism of EP additive action during the hot rolling process was also investigated. By analyzing the deformation behavior of the oxide scale of samples after hot rolling using different proportions of ZDDP, it was found that 20% ZDDP in the lubricant is the preferred concentration for industrial application.