Shock-resisting tool steels are among the strongest tool steels. They are
designated as group S steels according to the AISI classification system. These
steels include the S1, S2, S5, S6, and S7 type steels. The hardenability of
group S steels vary from shallow hardening to deep hardening.
In these steels, hardenability can be controlled by adjusting the composition
rather than the grain size and melting methods. However, higher austenitizing
temperatures are needed to obtain optimum hardness. Type S1, S5, and S6 steels
are oil quenched and type S2 steels are water quenched. Type S7 steels are
usually air-cooled, but the larger sections are oil quenched.
The primary alloying elements in shock-resisting tool steels are the
- Small amounts of carbon (0.4% to 0.6%)
Usually molybdenum, chromium and manganese are added to tool steels to give
them hardenability and tempering resistance. In S type steels, silicon is also
added to not only enhance tempering resistance of tool steels,
but also forms a microstructure, which resists deformation, under some
The key properties of shock-resisting tool steels are the following:
- High strength
- High toughness
- Wear resistance
- High hardness
- Resistance to shock loading
The following table shows the designation and composition limits of
shock-resisting tool steels.
aExcept group W, all steels contain 0.03 max S, 0.03
max P and 0.25 max Cu. Group W contain 0.025 max S, 0.025 max P, and 0.20 max
Cu. As mentioned, the amount of sulfur may be increased from 0.06% to 0.15% to
enhance the machinability of group A, M, T, H and D
The major applications of the shock-resisting tool steels are the
- Rivet sets
- Screw driver
- Shear blades
- Knockout pins
- Driver bits.