Oxidational wear modelling Part III. The effects of speed and elevated temperatures

This paper compares the theoretical and experimental divisions of heat during the oxidational wear of a tribe-system consisting of a high-chromium ferritic steel pin and an austenitic stainless steel disk, a system chosen in order to simulate the materials and the sliding motions occurring in the exhaust valve systems of typical diesel engines. These engines sometimes exhibit valve seat wear (sometimes known as 'valve sinkage'). The pin and disk in the laboratory simulation were slid against each other without any conventional lubricant at several loads from 12.5 to 75 N, at several speeds from 0.23 to 3.3 m s(-1), and at several externally induced disk temperatures from 200 to 500 degrees C. For the varying speed experiments, the disk temperatures were those originating from frictional heating only. For the varying disk temperatures experiments, the speed was maintained at 2.0 m s(-1). The object of comparing the experimental and theoretical divisions of heat was to determine (i) the number of thermally conducting contacts between these tribe-elements at any given instant, and (ii) the temperature at these contacts. Since these contacts are also the sites of oxidational wear, the paper describes how to use the computed values of these two parameters as inputs into a computer programme (based on the General Theory of Oxidational Wear) designed to provide values of the tribological oxidation constants required to make the theoretical oxidational wear rates equal to the experimentally measured oxidational wear rates to any required accuracy. The relevance of oxidational wear modelling for predicting the wear rates of practical tribe-systems is briefly discussed. (C) 1998 Elsevier Science S.A. All rights reserved.