Wear mechanisms experienced by a work roll grade high speed steel under different environmental conditions

Abstract

High speed steels are used for the manufacture of hot mill work rolls. The rolls suffer a variety of degradation mechanisms, of which abrasive wear and thermal fatigue are the most understood. However, what is less well characterised is the role that oxidation contributes to the deterioration of the roll surface. In particular, the roll surface undergoes rapid thermal cycles (possibly up to 650 °C in one roll rotation), and is subjected to a high humidity environment, and of course, significant cyclic contact stresses. In this work, the relationship between the friction and wear of a work roll grade high speed steel (1.55% C, 7.70% Cr, 4.90% V, 2.00% Mo) and oxidation was investigated at 400, 500 and 600 °C for two different environmental conditions (water, both gaseous and liquid, and laboratory dry air). A rolling-sliding disc on disc configuration was employed with a 25 N load for a sliding distance of 111 km. The specific wear rate of the high speed steel discs was greater for the tests conducted in laboratory dry air compared to the tests with the presence of water. However, the specific wear rate of the dry tests was strongly temperature dependent, while for the wet tests, the wear rate was insensitive to temperature. The dry tests exhibited a combination of metallic and oxidational wear, while the wet tests were almost entirely oxidational, with a different oxide phase constitution to the dry tests. Surprisingly, the wet tests exhibited higher friction compared to the wet tests. The reasons for this and the difference in wear rates are discussed and related to the phase constitution of the oxide layer and the amount of oxide formed in each experimental condition.