Study on the Formation of Scale Layer on Work Rolls in Hot Rolling

Abstract

In hot strip mill, the surface of steel based Adamite work rolls are covered with black scale layer, which is considered to be mainly Fe₃O₄. It has been reported that the scale layer was transfered from rolled stock or was the oxide of roll material. To study the formation mechanism of scale layerappearing on work rolls, experiments have been done using a model four-high rolling mill with scale breaker, and the results has been discussed. Main experimental results are as follows:
1) In the case of rolling without descaling or taking long time after descaling, work rolls were not covered with black scale layer without regard to water cooling on work rolls.
2) In the case of rolling with descaling rolled stock and water cooling on work rolls, steel based adamite and stainless steel work rolls were covered with black scale layer.
Prior mechanism does not explain the results of experiment. Then, the following mechanism can be proposed. The scale layer on work rolls is formed by corrosion reaction between water and rolled stock of metallic state in roll gap; the scale layer is composed of the most part of magnetite produced by the following reaction; Fe+2H₂O→Fe (OH) ₂+H₂ and 3Fe (OH) ₂→Fe₃O₄+2H₂O+H₂, that is 3Fe+4H₂O, Fe₃O₄+4H₂