O2 Tool Steel - Oil-Hardening Cold-Work Steel (UNS T31502)

Topics Covered

Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations


Cold-work tool steels belong to the family of high carbon steels that are further classified into oil-hardening steels, high-carbon, high-chromium steels, and air-hardening steels. Oil-hardening cold-work steels are also known as group O steels consisting of O1, O2, O6, and O7 types.

The following datasheet provides details about the O2 type steels. The O2 oil-hardening cold-work steel is alloyed with manganese.

Chemical Composition

The following table shows the chemical composition of O2 tools steels.

Element Content (%)
Manganese, Mn 1.40-1.80
Carbon, C 0.85-0.95
Silicon, Si 0.5
Chromium, Cr 0.35
Nickel, Ni 0.3
Molybdenum, Mo 0.3
Vanadium, V 0.3
Copper, Cu 0.25
Phosphorus, P 0.03
Sulfur,S 0.03

Physical Properties

The physical properties of O2 tool steels are outlined in the following table.

Properties Conditions
T (°C) Treatment
Density 7.66 x 1000 kg/m3 25 -

Mechanical Properties

The mechanical properties of O2 steels are tabulated below.

Properties Conditions
T (°C) Treatment
Poisson's ratio 0.27-0.30 25 -
Elastic modulus 27557-30458 ksi 25 -

Thermal Properties

The table below shows the thermal properties of O2 tool steels.

Properties Conditions
T (°C) Treatment
Thermal expansion 11.2 x 10-6/ºC 20-100 -

Other Designations

Other designations that are equivalent to O2 tool steels include:

  • ASTM A681
  • DIN 1.2842
  • SAE J437
  • SAE J438
  • UNS T31502
  • AFNOR 90 MV 8
  • UNI 88 Mn V 8 KU
  • B.S. Bo 2
  • FED QQ-T-570

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