AISI A2 Air-Hardening Cold Work Tool Steel: Distortion-Free Grade
ASTM A681 · Published: 2026-06-01 · Updated: 2026-06-02
AISI A2 is a 5% chromium air-hardening cold work tool steel (0.95-1.05% C, 4.75-5.50% Cr, 0.90-1.40% Mo, 0.15-0.50% V)—the intermediate choice between O1 (oil-hardening, lower wear) and D2 (high Cr, higher wear, lower toughness). A2 hardens from...
AISI A2 is a 5% chromium air-hardening cold work tool steel (0.95-1.05% C, 4.75-5.50% Cr, 0.90-1.40% Mo, 0.15-0.50% V)—the intermediate choice between O1 (oil-hardening, lower wear) and D2 (high Cr, higher wear, lower toughness). A2 hardens from 925-980°C with air cooling—minimal distortion compared to oil quenching of O1—making it the choice for complex die shapes, thread rolling dies, coining dies, and precision gauges. The lower chromium carbide volume than D2 provides better toughness and grindability, while still offering significantly better wear resistance than O1. Achieves 58-62 HRC after tempering at 175-540°C. For maximum toughness (forming and blanking dies subject to chipping), temper at 480-540°C; for maximum wear resistance (gauges, shear blades), temper at 175-260°C.
Quick Facts
| Category | Tool Steel |
| Standard | ASTM A681 |
| Density | 7.85 g/cm³ |
| Yield Strength | 1,450 MPa (210 ksi) at 60 HRC |
| Tensile Strength | 1,760 MPa (255 ksi) at 60 HRC |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN X100CrMoV5 | Compare |
| DIN 1.2363 | Compare |
| SKD12 | Compare |
| Cr5Mo1V | Compare |
| JIS SKD12 | Compare |
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Frequently Asked Questions
Should A2 be double-tempered?
Yes, double tempering is recommended—especially for the secondary-hardening temper range (480-540°C). A2 contains approximately 5-10% retained austenite after air hardening; the first temper transforms this to fresh martensite; the second temper tempers the fresh martensite. For tools tempered below 260°C where retained austenite is stable, single tempering may be acceptable for non-critical applications, but double tempering is industry best practice.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu