The rolling sliding wear response of conventionally processed and spray formed high speed steel at ambient and elevated temperature

Abstract

The effect of spray forming on the wear properties of a 1.2C–3.4W–8.9Cr–4.3V–2.7Mo high speed steel is described. The microstructure, fracture behaviour and wear response of the spray cast materials are compared with those of conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale for both grain size and carbide size. In addition, large primary and interconnected eutectic carbides observed in the conventionally cast material were replaced by a more uniform distribution of discrete globular carbides in the spray cast material. This refinement is shown to give rise to an increase in the resistance to fracture. Wear testing was undertaken in the rolling/sliding configuration (8% slippage) at 300 N against an M2 tool steel counterface in the temperature range 20–650 °C. The wear rate of the conventional material was significantly higher than that of the spray cast material at all temperatures. Both adhesive and oxidative wear mechanisms were observed, with the latter becoming more prominent as the test temperature increased. Surface degradation occurred preferentially at the carbide/matrix interface for both materials, but was particularly prominent in the Fe/M 2C–M 6C eutectic regions and at large primary VC carbides in the conventionally cast material, resulting in higher rates of material loss in these regions. The improvement in wear resistance observed for the spray formed material can be directly attributed to the refinement of both primary and eutectic carbide phases and the elimination of microsegregation. The laboratory observations are compared to a worn surface of a spun cast hot mill work roll of nominally the same composition following a normal campaign in the roughing stands of a hot rolling mill. This showed that the wear mechanisms in the field were reproduced in the laboratory. The relationship between process parameters microstructure and wear mechanisms is discussed.