Base materials for taps
An important factor for the success of the work and the longevity of the tool is the material from which the taps are made. The steel used for production must have good resistance to deformation, high fracture resistance and optimum wear behavior.
Good taps are made from high-speed steel
The steels that serve as the base material for high-quality taps and other cutting tools all belong to the group of high-speed steels. These are also abbreviated to HSS after the English term High Speed Steel. These are high-alloy tool steels that are hard enough to withstand high temperatures without plastic deformation and at the same time tough enough not to break even under high loads. HSS is also easy to machine in the soft-annealed state and can be ground without any problems in the hardened state. This means that even complex geometries, such as those required for a tap, can be produced precisely and tools that have become blunt can also be reground without any problems.
Differences between HSS, HSSE and HSSE-PM
The group of high-performance high-speed steels can be subdivided into further subgroups according to alloy and manufacturing process, the properties of which are perfectly matched to specific cutting applications. HSS, HSSE and HSSE-PM are mainly used for taps.
HSS
HSS is the basic form of high-speed steel. The desired properties can be controlled by combining the alloying elements chromium, tungsten, vanadium, molybdenum and cobalt in various concentrations and compositions. If the tap is marked HSSG as the base material, this indicates a ground drill point, which improves precision and tool life.
HSSE
HSSE refers to a type of high-speed steel with a special focus on the alloying element cobalt. The cobalt content influences the high-speed steel's heat resistance; steel grades with a high cobalt content therefore have a higher hardness, heat resistance and tempering resistance. HSSE has a cobalt content of 5% to 8% and is suitable for particularly hard and difficult-to-machine materials. However, HSSE also has disadvantages, first and foremost its decreasing toughness, which is associated with a higher risk of breakage. Therefore, taps made of HSSE should only be used if the material to be machined actually makes it necessary. A variant of HSSE with an additionally increased vanadium content for a further increase in hardness is known as HSSE-V3.
HSSE-PM
The suffix PM does not describe alloying elements, but the manufacturing process. While HSS is usually produced using the melting metallurgical process, powder metallurgical production is used for HSSE-PM. The liquid steel is first atomized and then pressed. This produces a material that is particularly homogeneous. In addition, powder metallurgical production can achieve higher alloy contents. PM steels are highly resistant to wear and pressure, have a high hot hardness and are also characterized by high toughness and good machinability.