O7 Tool Steel - Oil-Hardening Cold-Work Steel (UNS T31507)

Topics Covered

Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Processing Properties
Other Designations


Cold-work tool steels are high carbon steels that are further classified into three subgroups such as 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.

Type O7 oil-hardening cold-work steel consists of chromium and manganese, and has higher tungsten content than type O1. The O7 steel has the best wear resistance among the O series steels, however, it has relatively low hardenability. The following datasheet provides details about the O7 type.

Chemical Composition

The following table shows the chemical composition of O7 tools steels.

Element Content (%)
Iron, Fe ~95%
Carbon, C 1.10-1.30
Manganese, Mn 1.00
Silicon, Si 0.60
Chromium, Cr 0.35-0.85
Nickel, Ni 0.30
Molybdenum, Mo 0.30
Tungsten, W 1.00-2.00
Vanadium, V 0.40
Copper, Cu 0.25
Phosphorous, P 0.03
Sulfur, S 0.03

Physical Properties

The physical properties of O7 tool steels are outlined in the following table.

Properties Metric Imperial
Density 7.80 g/cm3 0.282 lb/in3

Mechanical Properties

The mechanical properties of O7 steels are tabulated below.

Properties Metric Imperial
Hardness, Rockwell C 58.0-64.0 58.0-64.0
Bulk modulus 140 GPa 20300 ksi
Shear modulus 80.0 GPa 11600 ksi
Machinability (based on 1% carbon water-hardening tool steel) 85% 85%
Poisson's ratio (25°C) 0.27-0.30 0.27-0.30
Elastic modulus (25°C) 190-210 GPa 27557-30458 ksi

Thermal Properties

The table below shows the thermal properties of O7 tool steels.

Properties Metric Imperial
CTE, linear 11.2 mm/m°C 6.22 min/in°F

Processing Properties

The following table provides the processing properties of O7 tool steels.

Properties Metric Imperial
Processing temperature (tempering) 175-290°C 347-554°F
Processing temperature (hardening) 790-885°C 1450-1630°F
Annealing temperature 790-815°C 1450-1500°F

Other Designations

Other designations that are equivalent to AISI O7 tool steels include:

  • ASTM A681
  • FED QQ-T-570
  • UNS T31507


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