Tool knowledge

What Does S2 Mean on Tools' Steel Bits?

What Does S2 Mean on Tools' Steel Bits?

S2 alloy steel is a shock-resisting tool steel type. It retains good ductility even in hardened conditions, which allows it to perform in applications where shock impact is transmitted to the alloy. Shock-resisting tool steels like this are designated as group S steels.

Chemical Composition

The following table shows the chemical composition of S2 tool steels.

ElementContent (%)
Iron, Fe97.0
Carbon, C0.4-0.55
Molybdenum, Mo0.4
Manganese, Mn0.4
Vanadium, V≤0.5
Phosphorus, P≤0.03
Sulfur, S≤0.03

How strong is S2 alloy steel?

Physical PropertiesMetricEnglishComments

Mechanical PropertiesMetricEnglishComments
Hardness, Knoop624624Converted from Rockwell C Hardness.
Hardness, Rockwell C5555
Hardness, Vickers602602Converted from Rockwell C Hardness.
Tensile Strength, Ultimate2150MPa312000psi
Tensile Strength, Yield2000MPa290000psi
Elongation at Break7.0 %7.0 %in 50 mm
Bulk Modulus160GPa23200ksiTypical for steel
Shear Modulus80.0GPa11600ksiTypical for steel

Thermal PropertiesMetricEnglishComments
CTE, linear10.9µm/m-°C
@Temperature 20.0 - 100 °C
@Temperature 68.0 - 212 °F

@Temperature 0.000 - 300 °C
@Temperature 32.0 - 572 °F

@Temperature 0.000 - 500 °C
@Temperature 32.0 - 932 °F

Processing PropertiesMetricEnglishComments
Processing Temperature175- 425°C347- 797°FTempering Temperature

845- 900°C1550- 1650°FHardening Temperature
Annealing Temperature760- 790°C1400- 1450°F

Component Elements PropertiesMetricEnglishComments
Carbon, C0.40 - 0.55 %0.40 - 0.55 %
Iron, Fe97 %97 %As Balance
Manganese, Mn0.40 %0.40 %
Molybdenum, Mo0.40 %0.40 %
Phosphorus, P<= 0.030 %<= 0.030 %
Silicon, Si1.05 %1.05 %
Sulfur, S<= 0.030 %<= 0.030 %
Vanadium, V<= 0.50 %<= 0.50 %

Physical Properties

The physical properties of S2 tool steels are given in the following table.



7.79 g/cc

0.281 lb/in3

Melting point



Mechanical Properties

The mechanical properties of S2 tool steels are tabulated below.



T (°C)


Poisson's ratio




Elastic modulus

190-210 GPa



Thermal Properties

The following table shows the thermal properties of S2 tool steels.



T (°C)


Thermal expansion

10.9 x 10-6/ºC



Other Designations

Other designations that are equivalent to S2 tool steels include:

  • ASTM A681

  • FED QQ-T-570

  • SAE J437

  • SAE J438

  • UNS T41902

Fabrication and Heat Treatment


The machinability rating of S2 tool steels is 85% of that of the W group steels.


S2 tool steels are formed using conventional procedures under annealed conditions.


S2 tool steels are readily weldable using standard methods.

Heat Treatment

S2 tool steels are slowly preheated to 649ºC (1200ºF) and then directly heated by increasing the temperature to 871ºC (1600ºF). This is followed by holding the steels for 10 to 20 mins and quenching in brine or water.


Forging is carried out in S2 tool steels at temperatures ranging from 899 to 1093ºC (1650 to 2000ºF). Forging below 871ºC (1600ºF) is not preferred.

Cold Working

S2 tool steels can be cold-worked under annealed conditions.


Annealing is performed on S2 tool steels at 788ºC (1450ºF) followed by cooling in the furnace at a rate of not more than 4ºC per hour.


S2 tool steels are tempered at 177 to 427ºC (350 to 800ºF) to obtain Rockwell C hardness of 60 to 50.

Related Issues

How strong is S2 alloy steel? Applications for shock-resisting steels include springs, as well as chisels, dies for forging, and punches. S2 steel is also used to make Ball bearings for the mining industry. They are also used for screwdrivers and driver bits.

What is S2 tool steel used for?

【DURABLE S2 Material】: The bit socket head is made of S2 alloy steel, which is strong and has good toughness, not easy to break. It is the best material for making a bit set.

Is S2 steel hardened?

AISI Type S2 is a water-hardening tool steel with extreme toughness and resistance to shock loading. Even at a hardness of Rockwell C 59-60, it will bend before it breaks.

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