Evaluation of As-Hipped PM High Speed Steel for Production of Large-Diameter Cutting Tools

Abstract

Powder Metallurgy has been presented as an important process for producing metallic materials. Specially for high speed steels, it presents many advantages, as finer microstructures and alloy compositions that could not be feasible thought other processes. For large diameter bars, powder metallurgy is important because it produces more isotropic materials, with better carbide distribution, increasing the mechanical properties and notably the toughness. The present work aimed to characterize M3:2 high speed steel produced by powder metallurgy and compare its properties with conventional M2, in bar diameters between 76 and 91 mm. The steels were hardened using austenitizing temperatures varying between 1080 and 1200 °C; tempering was performed at 560 °C. For all austenitizing temperatures, bend toughness and microstructure were analysed and isotropy was evaluated comparing toughness values in transverse and longitudinal directions. The results show that, in the same hardness levels, PM M3:2 high speed steel is tougher than conventional M2. Besides, toughness in PM material is completely isotropic while M2 present differences in relation to the sample direction. Toughness results are closely related to the microstructure of materials, as PM material has a more homogeneous and finer distribution of primary carbides. Thus, the as-HIPed powder metallurgy high speed steel is shown as an important option to improve mechanical properties with maximum isotropy.