Influence of Surface Oxide Scale of Fe–Cr Alloy on Tool Lubrication Characteristic during Hot Rolling

Abstract

The surface oxide scale formed on steel products plays an important role of lubricating behavior during steel making process. However, there are few reports in detail about the influence of the oxide on lubricating properties. To investigate the effects of oxide scale of Fe–Cr alloy on lubricating properties, hot rolling test was carried out. As a tool material SKD61 was used. In order to change the scale structure of Fe–Cr alloy, dry air and steam containing gas were used as oxidation atmosphere condition.
In case of the oxidation in wet atmosphere, Fe₂O₃, Fe₃O₄ and FeO were formed as outer scale, and FeCr₂O₄ and FeO were formed as inner scale. On the other hand, for the oxidation in dry air, the scale structure were Fe₂O₃ and Fe₃O₄ for outer scale, and FeCr₂O₄ and Fe₃O₄ for inner scale. In case of oxidation in wet atmosphere before rolling, the scoring of hot work piece (Fe–Cr alloy) and tools (SKD61) was reduced. TEM observation suggested that surface scale containing FeO was deformed during hot rolling with hot work piece, and then all the surface of hot work piece was covered with scale. The reason for the improvement of scoring behavior by wet atmosphere was thought that FeO on hot work piece (Fe–Cr alloy) prevented the contact with tools (SKD61).