DEVELOPMENT OF IMPROVED CUTTING TOOL MATERIALS.

Abstract : New cutting tool alloys were developed for machining aerospace materials. Co-Cr and Fe-Co base alloys were prepared by hot-consolidation of atomized powders. Fe-50Co-20W-1.3C at R(C) 66 attained a transverse-rupture strength f 790,000 psi, an ultimate tensile strength of 443,000 psi, and had tool lives 2 to 3 times those of M40-type high-speed steels in peripheral end milling Ti-6Al-4V. Alloys of Fe-Co-W-C at 30-40% Co hardened to R(C) 72.5 and were superior to high-speed steels in turning Ti- and Ni-base alloys. Extrusion and edge-restraint rolling were used to fabricate 3 to 12 lb billets of atomized Fe-Co-W-C alloy powders. The bar stock was highly fabricable and defect-free. Composite bar stock was produced by extrusion or rolling jacketed Fe-Co base tool alloy powders on mild steel cores. High-melting matrix carbides based on TiC-Ni-Re were prepared by liquid-phase sintering. Small additions of Ta or W produced bend strengths up to 175,000 psi at R(A) 93; hardnesses of R(A) 86 were retained to 1500F. These carbides had 2 to 3 times the tool life of commercial C-8 grade carbides in turning AISI 4340 at R(C) 42. Arc-melted Hf-Ta alloys were hot rolled, machined, then nitrided to produce hard surface layers. (Author)