Lubrication effects on the surface quality control of hot rolled steels: A review

Lubricants play a significant role in hot steel rolling, for example, reducing the energy consumption of rolling mills, enhancing the service performance of work rolls, controlling the formation of oxide scales, and improving the surface quality of hot rolled products. The lubricants used in practical hot steel rolling have undergone a series of iterations in the past two decades, progressing from neat oils to oil-in-water emulsions and now to oil/water-based nanolubricants. Recently, with the goal of achieving green manufacturing and its sustainable development, eco-friendly water-based nanolubricants have attracted considerable attention as viable substitutes for traditional oil-containing lubricants, especially for the surface quality control of hot rolled steels. This review begins by summarising the application of various lubricants in hot carbon steel rolling, followed by examining the impacts of lubricants on the surface roughness, porosity and compactness of hot rolled steels. Then the lubrication mechanisms of different lubricants associated with hot steel rolling are discussed, particularly focusing on the unique role of nanoadditives in lubricants. Finally, methodical analyses of the thickness, phase compositions, and formation mechanisms of hot rolled steel surface oxide scales are elucidated. This work pioneers a comprehensive review of surface quality control strategies for hot rolled steels under different lubrication conditions and proposes the outlook for the future research in related fields.