Hard machining of PM high speed steels: The influence of material properties on hard milling process layout and resulting work piece surface properties

PM High-speed steels are increasingly important to meet the need for high strength and abrasion resistance of tools for cold work applications. Many investigations have been made regarding the influence of tooling material and surface properties on wear and fatigue behaviour. Nevertheless, the manufacturing route (milling, spark erosion, grinding) is determining tooling costs, delivery time and surface properties significantly. Especially hard milling has major advantages in manufacturing, while its influence on the tool quality is not well understood yet. The present work focuses on the influence of material properties such as carbide content, type and morphology on an optimum hard milling process layout regarding the surface properties of the tools. Material composition and heat treatment were chosen in order to isolate the influence of different material characteristics being caused by melt or PM fabrication, material composition and heat treatment. The investigation encompasses HS6-5-2 (PM and conventional) type materials as well as HS14-3-5PM in different heat treatment states and grain sizes. The presented results expand the known process models by attributing the machining mechanisms and its implications for the latter product (surface quality, subsurface properties) to the relevant material characteristics in order to enable a sophisticated and holistic process layout