Analysis of the friction and wear behavior of hot work tool scale: application to the hot rolling process

in hot forming processes, the interface tool/product is important for the q uality of the finished product. In hot rolling, the scale formed on the rol l material plays an essential role. As soon as the contact oxide-oxide is e stablished between the roll and the slab, friction allows the process to st art. However, the oxide scale will continue to grow under the cyclic action of hot contacts and water cooling, and will be subjected to thermo-mechani cal stresses. Beyond a certain critical thickness, the oxidized surface lay er of the cylinders has not sufficient mechanical strength to withstand the shear stresses. The wear and friction behavior of the oxides appearing on the surface of the hot working rolls is not well known. The influence of th ese oxides on the friction and, consequently, the quality of the products o f finishing mills, seems very significant. So, in this study, we investigat e the evolution of the friction coefficient and the wear, according to the growth, the nature and the thickness of the formed scale. We use a high tem perature pin on disc tribometer. The pin consists of material "rolls" while the disc consists of the slab. The pin is instrumented with thermocouples in order to couple the friction coefficient measurements with the thermal g radient in the pin and the surface temperature and the formed oxides, Then, the characterization of the surfaces is done by scanning electronic micros copy (SEM) and EDS analyses. We use the method of sin(2) Psi to evaluate re sidual stresses of oxide and correlate these data with shear stress behavio r. (C) 2001 Elsevier Science B.V. All rights reserved.