Tool steels- Chemical composition and structure

Tool steels are used, as their name suggests, in all problems involving the shaping of materials in the broadest sense. They can be used for machining operations (turning, drilling, milling...), cold and hot forming (sheet metal working under press by cutting and stamping, forging and hot stamping, cold or hot rolling), casting (gravity or pressure die-casting of aluminum, copper, zinc and magnesium alloys, copper, zinc and magnesium alloys, glass packaging, rubber industry, plastics processing), extrusion (light steels and alloys, copper alloys, titanium and zirconium alloys, plastics, cellulose pulp...). Tool steels are an integral part of the special steels sector, but they differ significantly from mechanical engineering steels, both in terms of the conditions under which they are used, and in terms of the use criteria used to define them. In the case of quality tools, the aim is to achieve maximum performance, without setting an upper limit, whereas engineering steels must be sufficiently fit for purpose, with specific, well-defined characteristics such as fatigue strength, resistance to impact and sudden fracture, machinability and the ability to undergo a thermo-mechanical forging cycle or quality heat treatment during processing. However, in view of increasing tool life requirements, the metallurgical challenges faced by this group of steels are similar to those faced by high endurance steels used in the aerospace industry.

What's more, in most cases, the tool is subjected to the most severe stresses on its surface, whereas structural steels are subjected to stresses throughout the entire material. As a result, tool steels cannot be defined by means of simple behavior laws, and it is necessary to have the most precise possible knowledge of stress conditions in order to provide realistic selection criteria. The solutions adopted are the result of an essentially pragmatic approach, and represent compromises between often contradictory requirements.

For further details on this subject, the reader is invited to consult the bibliographical references presented in the background section of this article.