Sep 13 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesOther Designations
Introduction
Steels of the type A2, A3, A4, A6, A7, A8, A9, and A10 form 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 a thickness of at least 100 mm (4 in.) in diameter when air cooled.
Carbon is present in the range of 0.5 to 2% in group A steels. These steels are provided with air hardening characteristics that allow minimum cracking and distortion on quenching.
The sections below will provide an overview of A4 air-hardening, medium-alloy, cold-work tool steels.
Chemical Composition
The chemical composition of A4 tool steels is outlined in the following table.
| Element |
Content (%) |
| C |
0.95-1.05 |
| Mn |
1.80-2.20 |
| Si |
0.50 |
| Cr |
0.90-2.20 |
| Ni |
0.30 |
| Mo |
0.90-1.40 |
| Cu |
0.25 |
| P |
0.03 |
| S |
0.03 |
Physical Properties
The following table shows the physical properties of A4 tool steels.
| Properties |
Metric |
Imperial |
| Density |
8.03 g/cm3 |
0.290 lb/in3 |
Mechanical Properties
The mechanical properties of A4 tool steels are displayed in the following table.
| Properties |
Metric |
Imperial |
| Hardness, Rockwell C (as air quenched from 845°C, 61 HRC at 150°C temper, 60 HRC at 205°C temper, 59 HRC at 260°C temper, 58 HRC at 315°C temper, 57 HRC at 370°C temper, 56 HRC at 425°C temper, 54 HRC at 480°C temper, 53 HRC at 540°C temper, 50 HRC at 595°C temper, 40 HRC at 650°C temper.) |
63 |
63 |
| Bulk modulus (typical for steels) |
140 GPa |
20300 ksi |
| Machinability (based on carbon tool steel) |
65% |
65% |
| Shear modulus (typical for steels) |
80.0 GPa |
11600 ksi |
| Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
| Elastic modulus |
190-210 GPa |
27557-30457 ksi |
Other Designations
Equivalent materials to A4 tool steels are:
- ASTM A681
- FED QQ-T-570
- UNS T30104