Influence of the Iron Oxide Layer on Lubricating Properties in Seamless Pipe Hot Rolling

Abstract

It is well known that an iron oxide layer formed on a surface of work piece plays an important role of lubricating properties in hot rolling. However, a few papers fully reported the influence of the iron oxide layer on lubricating properties. Therefore, we investigated the influence of compositions and thickness of the iron oxide layer on lubricity by means of a simulation test of semless pipe hot rolling.
First, some iron-oxide layers of various compositions and thickness were formed on three different steel materials by oxidizing treatment under different conditions: where the work pieces were exposed to air until the oxide layer grew to the set thickness. Then, the hot work piece was rolled between a cylindrical roll and a flat tool lubricated with graphite-based lubricant. The friction coefficient was measured during rolling, and the flat tool surface was observed after rolling.
Summaries of the results are shown below.
① In case the rolled material was carbon steel, scoring didn't occur regardless of its elongation in the test condition. On the other hand, in case the rolled material was 10% Cr steel or 18%Cr–8%Ni stainless steel, scoring occurred when the elongation was high.
② The abovementioned results are thought to be caused that the scale of FeO generated in the case of carbon steel has high plasticity at elevated temperature.