Mechanism of oxide scale to decrease friction in hot steel rolling

In hot rolling processes, an oxide scale is formed on steels by high-temperature oxidation. It was reported that rolling load, forward slip and redundant shear deformation decrease with increasing scale thickness. Therefore the scale can be regarded as a lubricant to decrease friction in hot rolling. However, it is still unclear why the scale shows the apparent lubricating effects. As bonding between the scale and the steel is weak, relative sliding of the scale with respect to the matrix steel could be a major mechanism. In order to observe the relative sliding experimentally, a pin of austenitic stainless steel was embedded into a low-carbon steel sheet. The sheet was heated to 1273 K or 1373 K under argon, oxidized under air for prescribed duration, then hot-rolled. The scale moved to the rolling direction with respect to the matrix steel during rolling. The amount of the relative sliding increased with an increase in scale thickness. The forward slip decreased with increasing sliding distance. It is concluded that the relative sliding of the scale is responsible for the apparent lubricating effect. (C) 2018 The Authors. Published by Elsevier B.V.