A8 Tool Steel - Air-Hardening, Medium-Alloy, Cold-Work Steels

Topics Covered

Chemical Composition
Physical Properties
Mechanical Properties
Other Designations


Air-hardening, medium alloy, cold work steels also known as group A steels include A2, A3, A4, A6, A7, A8, A9, and A10. Sufficient amounts of manganese, molybdenum and chromium present in group A steels provide full hardness in sections comprising thickness of at least 100 mm (4 in.) in diameter when air cooled.

Group A steels have a carbon content of 0.5 to 2%. These steels have air hardening characteristics that allow minimum cracking and distortion on quenching.

The data below will provide an overview of A8 air-hardening, medium-alloy, cold-work tool steels.

Chemical Composition

The chemical composition of A8 tool steels is outlined in the following table.

Element Content (%)
Chromium, Cr 4.75-5.50
Molybdenum, Mo 1.15-1.65
Tungsten, W 1.00-1.50
Silicon, Si 0.75-1.10
Carbon, C 0.50-0.60
Manganese, Mn 0.5
Nickel, Ni 0.3
Copper, Cu 0.25
Phosphorus, P 0.03
Sulfur, S 0.03

Physical Properties

The following table shows the physical properties of A8 tool steels.

Properties Metric Imperial
Density 7.87 g/cm³ 0.284 lb/in³

Mechanical Properties

The mechanical properties of A8 tool steels are displayed in the following table.

Properties Metric Imperial
Poisson's ratio 0.27-0.30 0.27-0.30
Elastic modulus 190-210 GPa 27557-30457 ksi
Bulk Modulus (typical for steels) 140 GPa 20300 ksi
Shear modulus (typical for steels) 80 GPa 11600 ksi
Hardness, Rockwell C 48 - 57 48 - 57
Machinability (based on carbon tool steel) 65 65

Other Designations

Equivalent materials to A8 tool steels are:

  • ASTM A681
  • FED QQ-T-570
  • UNS T30108

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