Analysis of Rolling Force and Friction in Hot Steel Rolling with Water‐Based Nanolubrication

Water‐based nanolubricants are playing increasingly important roles in hot steel rolling over the past decade regarding environmental protection, energy saving, and product quality improvement. The contact friction between the work roll and the workpiece under water‐based nanolubrication, however, has been scarcely investigated. In this study, water‐based lubricants containing 0–4.0 wt% TiO2 nanoparticles are employed in hot rolling of a mild steel under different rolling conditions. The Taguchi method is used for the orthogonal design of the hot‐rolling tests to sequence the key factors that affect the rolling force in terms of importance. The as‐synthesized water‐based nanolubricants indicate excellent dispersion stability after standing for 24 h, which can be readily restored to the original state via manual shaking. The coefficient of friction (COF) during the steady‐state hot steel rolling is inversely calculated using a flow stress model developed from hot compression testing. A novel COF model for hot rolling of the steel is thus proposed through multiple linear regression. It is found that the result of linear regression agreed well with that of inverse calculation, indicating that the proposed COF model is applicable. Finally, the lubrication mechanism is examined through a boundary lubrication regime determined from a modified lubricant film thickness model.