Effects of Oxide Scale on the Corrosion and Mechanical Properties for a High Speed Steel and a Graphite Cast Iron

The mechanical properties and the oxidation characteristics of the high speed steel (HSS) for hot-rolling process, produced by centrifugal casting process, were investigated experimentally. Because of the complicated microstructure with tiny V-, Cr-, and W-based precipitations in the matrix, high hardness of the HSS samples was obtained. Moreover, high compressive strength and high compressive strain were detected, while low tensile properties were obtained. In spite of the high hardness of HSS, the wear resistance was a low level due to severe oxidation on the HSS surface and generated cracks, but the wear resistance of HSS was still better than conventional graphite cast iron. Although the corrosion occurred by the wear test, no clear microstructural change was detected. Wear and corrosion characteristics were examined at high temperatures and high humidity using an originally proposed testing machine. With this testing machine, failure characteristics of HSS were clarified, in which the HSS sample was worn away easily due to the brittle oxidation scale during the rolling process, leading to the rough HSS surface. Furthermore, the low tensile strength of HSS made an acceleration of the failure especially crack growth. Such rough surface has made reduction in the quality of the rolled materials.