Chapter 6 - Cutting tool materials I: High speed steels

Abstract

Metal cutting tools are subjected to a tremendous range of environments. The pressures of technological change and economic competition have imposed demands of increasing severity. To meet these requirements, new tool materials are sought and a very large number of different materials should be tried. The novel tool materials, which have passed the trials, are the products of the persistent effort of thousands of crafts-people, inventors, technologists and scientists, blacksmiths, engineers, metallurgists, and chemists. The tool materials, which have survived and are commercially available are those that have proved fittest to satisfy the demands put upon them. The agents of this “natural selection” are the machinists, tool-room supervisors, tooling specialists, and buyers in the engineering factories, who effectively decide which of all the potential tool materials shall survive. The only tool material for metal cutting from the beginning of the Industrial Revolution until the 1860s was carbon tool steel. Prolonged industrial experience was the guide to the selection of optimum carbon content for particular cutting operations. High speed steels give a modest improvement in the speed at which steel could be cut compared with carbon steel tools. The properties of high-speed tools are the result of precipitation hardening within the martensitic structure of the chromium, tungsten, molybdenum, and vanadium tool steels after a very high temperature heat treatment. Coating of tools with thin layers of TiN by a PVD process, which prolongs tool life in most situations and in others gives a smoother surface finish on the machined part.