Reference & Charts
Tool Steels
The common tool steel grades at a glance — O1, A2, D2, S7, H13, M2, W1, and P20 — with AISI class, nominal composition, typical working hardness, and what each is used for. Pick the right grade for dies, punches, cutting tools, and molds.
8 entries · Last verified: 2026-07-10
Tool steels are grouped by the AISI letter class that reflects how they harden or what they're for: W (water-hardening), O/A/D (cold-work — oil, air, and high-chromium), S (shock-resisting), H (hot-work), M/T (high-speed), and P (mold). Selection is a trade between wear resistance, toughness, and — for hot-work and high-speed grades — how much hardness the steel keeps at temperature. Compositions below are nominal and the hardness ranges are typical working values; the achievable properties depend on the heat treatment and section size.
| Tool Steel | AISI class | Carbon(%C) | Key alloying | Working hardness(HRC) | Wear resistance | Toughness |
|---|---|---|---|---|---|---|
| O1 | O — oil-hardening | 0.9 %C | Mn, Cr, W | 57–62 | Moderate | Moderate |
| A2 | A — air-hardening | 1 %C | 5% Cr, Mo, V | 57–62 | Good | Good |
| D2 | D — high-C high-Cr | 1.5 %C | 12% Cr, Mo, V | 58–62 | Excellent | Low |
| S7 | S — shock-resisting | 0.5 %C | Cr, Mo | 54–58 | Moderate | Excellent |
| H13 | H — hot-work | 0.4 %C | 5% Cr, Mo, V | 44–52 | Good | Good |
| M2 | M — high-speed (Mo) | 0.85 %C | Mo, W, Cr, V | 62–65 | Excellent | Moderate |
| W1 | W — water-hardening | 1 %C | (plain carbon) | 58–64 | Moderate | Moderate |
| P20 | P — mold steel | 0.35 %C | Cr, Mo | 28–34 | Moderate | Good |
Select a tool steel for its full spec sheet.
Frequently asked
- A2 vs D2 — which cold-work grade?
- D2 has much higher wear resistance and edge retention for long production runs, but it's brittle. A2 gives up some wear resistance for markedly better toughness and the same low-distortion air hardening — the safer default unless wear life is the dominant concern.
- Which tool steel for impact or shock loading?
- S7. It's the shock-resisting grade — high toughness and impact resistance at a useful hardness (54–58 HRC). Use it for chisels, punches, and shear blades where a wear-optimised grade like D2 would chip or crack.
- Are these exact compositions and hardnesses?
- No — they're nominal AISI compositions and typical working-hardness ranges for selection. Exact chemistry and achievable hardness depend on the specific supplier's grade and your heat-treat spec and section size. Work from the mill certification and heat-treatment data for production tooling.
Sources
- AISI tool-steel classification (type letters and nominal compositions)
- ASM International — Tool Steels / Heat Treater's Guide (typical properties and working hardness)