Assessment of oxide scales influence on wear damage of HSM work rolls

Improvement of hot rolling process involves the lengthening of rolling campaigns. This can be achieved through the wear resistance improvement of work roll grades. The wear damage observed in service on the hot working rolls is the result of a complex interaction between oxidation, friction and thermal fatigue. An approach is to assess the coupled effect of oxidation and friction on the overall tribological behaviour at high temperature. A first step consists in a good knowledge of the material behaviour against each stress.Tribological behaviour of roll grades at high temperature is indeed strongly affected by the nature, the thickness and the thermo-mechanical properties of their oxide scales involved into the contact. All these parameters depend on roll grade microstructure.An experimental methodology has also been performed to assess the influence of the roll grade microstructure on their tribological behaviour at high temperature. It constitutes the subject of the present paper.Results have focussed on high temperature friction tests and on the analysis of oxide morphologies (through TGA tests and environmental SEM, ESEM, observations). Nevertheless this approach does not aim to reproduce strictly rolling conditions, but only to analyse the chemical and mechanical response of roll grades regarding thermal and mechanical stresses involved in hot rolling.Material investigations have shown heterogeneous oxidation according to the different microstructural states and the environmental testing conditions. A particular scale roughness, depending on grades and oxidation conditions, and influencing the tribological behaviour, has been brought out.