Development of Dispersion-Hardened Cobalt-Base Cutting-Tool Alloys from Atomized Powders

Abstract

The atomizing process for manufacturing prealloyed powders has been used for the preparation of extremely fine dispersions in metal matrices. Using this process, fine hard carbides of titanium and columbium were produced in transition-metal matrices. As these carbides exhibited stability over wide temperature ranges, excellent base materials for cutting-tool compositions were provided. Of these, the cobalt-base alloys appeared most attractive. Cobalt-base compositions containing at least 30% of carbide formers, such as titanium, columbium, tungsten, molybdenum, and chromium, with carbon, were prepared as atomized powders. These powders were consolidated by extrusion into high-density bars with hardnesses approaching Rockwell 70C. Tools prepared from the extruded powders were evaluated in turning tests. At a hardness of Rockwell 61C., tools prepared from powders performed significantly better than conventional tool steel alloys and were comparable to a commercial cast tool in the machining of an austenitic stainless steel grade. At higher hardnesses of approximately Rockwell 70C., tools prepared from the extruded powder had a life of two to three times the life of a cast tool composition in the machining of a heat-treated SAE 4340 test log.