A6 Tool Steel - Air-Hardening, Medium-Alloy, Cold-Work Steels

Topics Covered

Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations


Steels of the type A2, A3, A4, A6, A7, A8, A9, and A10 are called air-hardening, medium alloy, cold work steels or group A steels. 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.

The carbon content group A steels range from 0.5 to 2%. These steels are provided with air hardening characteristics that allow minimum cracking and distortion on quenching.

The data below will provide an overview of A6 air-hardening, medium-alloy, cold-work tool steels.

Chemical Composition

The chemical composition of A6 tool steels is outlined in the following table.

Element Content (%)
C 0.65-0.75
Mn 1.80-2.50
Si 0.5
Cr 0.90-1.20
Ni 0.3
Mo 0.90-1.40
Cu 0.25
P 0.03
S 0.03

Physical Properties

The following table shows the physical properties of A6 tool steels.

Properties Metric Imperial
Density 8.03 g/cm3 0.290 lb/in3

Mechanical Properties

The mechanical properties of A6 tool steels are displayed in the following table.

Properties Metric Imperial
Hardness, Rockwell C (as air quenched from 845°C, tempered for 2 hours. 61-62 HRC at 95°C temper, 60-61 HRC at 150°C temper, 58-59 HRC at 205°C temper, 56-57 HRC at 260°C temper, 55-56 HRC at 315°C temper, 52-53 HRC at 425°C temper, 50-51 HRC at 480°C temper, 48-49 HRC at 540°C temper) 61.0-62.0 61.0-62.0
Bulk modulus (typical for steels) 140 GPa 20300 ksi
Machinability (based on carbon tool steel) 65% 65%
Shear modulus (estimated from elastic modulus) 77.0 GPa 11200 ksi
Poisson's ratio 0.27-0.30 0.27-0.30
Elastic modulus 190-210 GPa 27557-30457 ksi

Thermal Properties

The thermal properties of A6 tool steels are given in the following table.

Properties Conditions
T (°C) Treatment
Thermal expansion 11.5 x 10-6/ºC 20-100 -

Other Designations

Equivalent materials to A2 tool steels are:

  • ASTM A68i
  • FED QQ-T-570
  • UNS T30i06
  • ASTM A681 (A-6)
  • UNS T30106

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