Punches & dies
Blanking, piercing, forming dies. The cold-work tooling default — air-hardening keeps tool dimensions on plan after HT.
Air-hardening tool steel · UNS T30102
A2 Tool Steel
The standard cold-work tool steel. Air-hardens with minimal distortion to 60–62 HRC, retains good toughness for a tool steel, and is widely available. Punches, dies, gauges, fixturing components — the workhorse of any tool room.
Hardness
60-62 HRC
Density
7.86 g/cc
Modulus
207 GPa
Mach. (ann.)
70 /100
When to use
Pick A2 when wear matters and air-hardening is a feature.
A2 is the moderate-alloy, moderate-toughness, moderate-cost cold-work tool steel — the default for punches, blanking dies, forming tools, gauges, and high-wear fixtures. Compared to D2 (more wear-resistant but more brittle) or O1 (oil-hardening, more distortion), A2 sits in the sweet spot of most tooling applications.
The big feature is air hardening. Heat to 950–980 °C, hold, then air-cool — A2 reaches 62 HRC without quenching. That dramatically reduces distortion compared to oil- or water-quenched grades, which is why precision tooling (gauges, master plates) routes through A2.
Strengths
Why it’s the tool-room default.
- Air-hardening = low distortionHeat treat with minimal dimensional change. Critical for gauges and precision fixturing.
- 62 HRC achievableWear and abrasion resistance for production tooling. Through-hardens up to ~75 mm sections.
- Tougher than D2Charpy impact ~13 J at 60 HRC vs ~5 J for D2. Less chipping on impact-loaded tools.
- Better wear than O1 / S7Higher hardness ceiling and better edge retention than O1; tougher than D2.
- Stocked widelySquare bar, rect bar, plate, drill rod — readily available in inch and metric sizes.
- Grindable post-hardeningStandard cylindrical and surface grinding finishes A2 to mirror tolerance.
Trade-offs
What you give up.
- Less wear than D2If your tool sees abrasive wear (sand, fiberglass, hardened parts), D2 lasts longer.
- Less toughness than S7For high-impact shock loading (heavy stamping, breakers), S7 is the tougher choice.
- Will rustNo corrosion resistance. Oil or VCI-treat between use; not for outdoor service.
- Hardness limits machinabilityOnce hardened, A2 is grind-only territory. Plan all machining in annealed condition.
- Distortion isn't zeroBetter than O1, but not perfect. ±0.0005″ is realistic; tighter requires post-hardening grinding.
- Limited high-temp serviceTempering above 200 °C drops hardness. Not for hot-work tooling — use H13 instead.
Specs
Mechanical, physical & chemical data.
Properties for A2 in standard hardened condition (austenitize 950–980 °C, air-cool, temper 175–200 °C × 2 hr) — yielding 60–62 HRC. Annealed properties shown for comparison.
Mechanical
Properties
| Hardness (annealed) | ≤ 235 HB / 98 HRB |
|---|---|
| Hardness (HT typical) | 60–62 HRC |
| Hardness (HT max) | 63–64 HRC |
| UTS (annealed) | 620 MPa (90 ksi) |
| UTS (HT) | ~2000 MPa (290 ksi) |
| Yield strength (HT) | ~1900 MPa |
| Modulus of elasticity | 207 GPa |
| Charpy V-notch (60 HRC)Higher than D2 | 13 J |
| Compressive strength (HT) | ~3100 MPa |
Source: Crucible Industries / Carpenter datasheets. Tempering above 200 °C drops hardness rapidly — design accordingly.
Physical & thermal
At room temperature
| Density | 7.86 g/cc (0.284 lb/in³) |
|---|---|
| Specific heat | 0.460 J/g·°C |
| Thermal conductivity | 26 W/m·K |
| CTE (20–100 °C) | 10.7 µm/m·°C |
| Austenitize temp | 950 – 980 °C |
| Critical temp (Ac1) | 770 °C |
| Quench medium | Air (preferred) or oil |
| Magnetic | Ferromagnetic |
Air-quench eliminates the rapid temperature gradient that causes oil-quench distortion. Sections > 75 mm may require oil quench for full hardening.
Composition
Chemistry, weight %
| Carbon (C) | 0.95 – 1.05 |
|---|---|
| Chromium (Cr) | 4.75 – 5.50 |
| Molybdenum (Mo) | 0.90 – 1.40 |
| Vanadium (V) | 0.15 – 0.50 |
| Manganese (Mn) | 1.00 max |
| Silicon (Si) | 0.50 max |
| Phosphorus (P) | 0.030 max |
| Sulfur (S) | 0.030 max |
| Iron (Fe) | balance |
The Cr-Mo-V combination is what makes A2 air-hardening — without those alloys, plain carbon steel would need oil or water quench.
Specifications
Common purchase specs.
ASTM A681
Tool steels — alloy
AISI A2 / SAE A2
Standard designation
UNS T30102
Unified numbering system
FED-QQ-T-570
Federal tool steel spec
JIS SKD12
Japanese equivalent
DIN 1.2363
European equivalent (X100CrMoV5-1)
Machining
Machining considerations.
Always machine annealed. After hardening to 60+ HRC, A2 becomes grind- or EDM-only territory. The standard workflow: rough machine with stock allowance → harden → finish-grind to size.
Cutting speed (annealed)
150–250 SFM with carbide. HSS works for low volume; not the right choice for production.
Feed rate
Aggressive constant feed. Annealed A2 cuts smoothly with continuous chips.
Tooling
Coated carbide (TiAlN, AlTiN) standard. Replace before significant wear — A2 dulls tools faster than 4140.
Coolant
Flood. Helps chip evacuation and surface finish.
Stock allowance
Leave 0.005–0.020″ on critical surfaces for post-HT grinding. More on thinner sections that may distort.
EDM after HT
Wire EDM cuts 60+ HRC A2 at the same speed as annealed material. Use it for sharp internal corners post-hardening.
Surface grinding post-HT
Standard finish operation. Aluminum oxide wheels for general use; CBN for production.
Stress-relieve before HT
If significant material was removed during machining, stress-relieve at ~650 °C before hardening to reduce HT distortion.
Applications
Where A2 shows up.
Gauges & masters
Inspection gauges, master plates, fixture components. Low distortion through HT lets gauges hold 0.0001″.
Production fixturing
Soft-jaw blanks for CNC, locating pins, hardened bushings. Wear surfaces in production fixtures.
Compare
Related tool steels.
More wear
D2 Tool Steel
12% chromium content gives much better wear resistance — for stamping abrasive material, fiberglass, hardened parts. More brittle than A2.
More toughness
S7 Tool Steel
Shock-resistant grade for impact tooling — chisels, breakers, heavy stamping. Lower hardness ceiling (~58 HRC) but much higher Charpy.
Hot work
H13 Tool Steel
For die-casting, hot forging, and tooling that runs at 500+ °C. Holds hardness where A2 would soften.
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