Tool steels are a group of steel grades that have high hardness, toughness and wear resistance resulted from appropriate heat treatment. These properties are required for metal conditioning, shaping or cutting.
According to their application tool steels can be grouped as follows:
- steels for measuring tools, low-alloy and carbon steels;
steels for cutting tools, (high-speed steels) ledeburite class, heat resistant;
die steels for cold deformation, non-heat-resistant steels of hypereutectoid and ledeburite classes;
die steels for hot deformation, heat-resistant steels of hypoeutectoid, eutectoid and hypereutectoid classes.
Carbon tool steel
Carbon steels are marked with letter "Ó" in a grade designation with average content of carbon shown in 1/10-percent increments. These steels can be quality and high quality ones (with letter "A" at the end of a grade designation).
Carbon tool steels reveal a tendency to overheating resulted from absence of alloying elements and owing to this fact they have à very narrow range for heat treatment temperature
- 740-780 °C for steels Ó10 - Ó12;
- 730-750 °Ñ for steels Ó7, Ó8.
Initial metal structure after rolling influence the results of heat treatment. It is very difficult to transform lamellar perlite structure into globular perlite structure without intermediate normalizing.
These steels have a tendency to decarburization, especially steels Ó7- Ó10. Decarburization is not significant for steels with high carbon content (Ó12- Ó13), but these grades tend to form cementite network.
The main disadvantage of such steels is low hardenability and the tendency to overheating. Carbon tool steel is classified as the material for general application.
Alloy tool steel
Alloy tool steel has a number of advantages over carbon tool steel as it has better hardenability, wear resistance, impact strength, toughness and does not tend to overheat.
Silicon containing tool steel shows significant decarburization during annealing and it is difficult to obtain required hardness of the steel. Therefore such steel is held at 780-800°C for 4-6 hours. It finds an application in production of broaches, taps, reamers, dies, cutting punches, small tools of simple shape for processing non-metallic, non-ferrous and easily workable materials.
Steel grades ÕÃ and Õ have a great number of carbides increasing tool durability. They are used for production of broaches, taps, reamers, dies, cutting punches. These steels are not so liable to decarburization.
The grade ÕBÃ is one of the best tool steels. It has high abrasion resistance due to chromium and tungsten carbides, high hardenability due to manganese and fine grains due to tungsten. The steel is annealed at 780-800°C. It is characterized by low distortion level and allows producing long complex-shaped parts. XB5-type steel has very high hardness after quenching (HRC 67-68). This steel is used for production of small simple-shaped tools for hard metal processing.