Abstract The influence of scale on friction at the work-tool interface in hot metal working has been studied with the aid of the ring test technique. Although it has been recognized that scale reduces interfacial friction, it has not previously been possible to separate the effects of scale thickness and of scale composition. In the present work, techniques were developed to obtain specimens on which the scale consisted exclusively of one type of oxide. This enabled us to investigate the influence of both scale thickness and scale composition on interfacial friction. It has been found that the friction at the work-tool interface is influenced by both the thickness and the composition of the scale. Results of this work do not confirm previous suggestions that wustite plays a dominant role in the reduction of friction. In fact, under certain conditions, wustite reduces friction less than the other oxides of iron do.
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