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Tool Steel

Tool steels are high-carbon (0.5–2.3 % C) steels alloyed with chromium, vanadium, tungsten and molybdenum to form hard carbides, hardened and tempered to 55–66 HRC for parts that cut, punch, form or wear. The AISI letters describe the job: A (air-hardening) and D (high-carbon high-chromium) for cold-work dies, O (oil-hardening) for small tools and gauges, S (shock-resisting) for punches and chisels, H (hot-work) for die-casting and forging dies, M and T (high-speed) for cutting edges that run hot.

Popular tool steel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
D24507507.7PoorPoorWear-driven cold-work dies and long-run blades
A24707407.86FairPoorGeneral cold-work dies; low distortion
O14006907.85FairPoorGauges, knives, small in-house hardened tools
S75308307.83FairPoorChisels, punches, shear blades — shock loads
H135207607.8FairFairDie-casting, extrusion and hot-forging dies
M25709008.16FairPoorCutting tools, broaches, high-hardness punches
CPM 3V6009007.46PoorPoorPM steel: near-S7 toughness at 58–60 HRC

All 138 tool steel grades

Choose tool steel for

Punches, dies, shear and slitter blades, forming and drawing tools, gauges, knives, wear plates and guide rails, injection-mold inserts that see abrasive fill, die-casting and forging dies, broaches, reamers and form cutters — any part that must hold an edge or a hard surface above about 55 HRC.

Look elsewhere when

The part is a fixture or wear part that is content at 45 HRC (pre-hardened or nitrided 4140), it is an injection-mold cavity that will be polished and textured (P20, 718, NAK80 pre-hardened mold steels), it is a rolling bearing or hardened pin (52100), it is a hot part that must also resist scaling above 600 °C (heat-resistant stainless or nickel alloys), or it must be welded in service (S7 tolerates repair welding; D2 and M2 do not).

Yield strength against elongation at break, Tool steel among every steel grade

No materials in view have both of these properties.

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Tool steel by application

Stamping and forming dies
A2 for most punches and dies at 60–62 HRC; D2 or DC53 for long runs in abrasive stock; S7 for heavy blanking and coining where the edge chips before it wears. CPM 10V / A11 when D2 wears out too fast.
Shear blades and chisels
S7 or S5 at 54–58 HRC for impact; 6CrW2Si and S1 on the same job; O1 or 1.2510 for small knives and scraper blades at 60 HRC.
Hot-work tooling
H13 (1.2344, SKD61) for die-casting dies, extrusion dies and hot-forging inserts at 44–50 HRC, H11 (1.2343) where toughness matters more, H21 for the hottest forging dies with tungsten; all are gas-nitrided for soldering and erosion resistance.
Cutting edges and wear rails
M2 or M35 at 62–65 HRC for broaches, taps, form cutters and punch tips; M42 for 66–68 HRC cutting tools; D2 or CPM S30V for knife blades that also see corrosion; W1 / SK5 for hand tools hardened in water.

Working with tool steel

Machining
Machined in the annealed state (about 200–250 HB) — D2 and M2 are already abrasive and gummy at about 30–40 % of 1212 machinability, A2 and O1 easier. Leave 0.2–0.5 mm for the size and shape change in heat treatment, more on thin sections. After hardening: grinding, EDM, or hard milling with coated carbide up to about 62 HRC. EDM leaves a recast layer that must be stoned or ground off on fatigue-loaded edges.
Heat treatment
A2: 950–980 °C, air cool, temper 175–200 °C for 60–62 HRC. D2: 1,010–1,040 °C, air or pressure quench, double temper at 200 °C for 60–62 HRC or 500–540 °C for secondary hardening at 58–60. O1: 790–815 °C, oil, temper 175–200 °C. H13: 1,020–1,050 °C, double temper at 550–600 °C for 44–50 HRC. M2: 1,200–1,220 °C, salt or vacuum, triple temper at 550 °C for 63–65 HRC. Always double (or triple) temper; wrap or vacuum-treat to avoid decarburizing the surface.
Welding
Repair only, by a tool-steel welder: preheat to 300–450 °C (H13 higher), matching filler, slow cool and re-temper. S7 and H13 tolerate it; D2, M2 and O1 crack easily. Design tooling as inserts so a worn edge is replaced, not welded.
Finishing
Ground, lapped and polished; PVD coatings (TiN, TiAlN, CrN) applied at 200–500 °C add wear life to punches and forming tools — the coating temperature must stay below the tempering temperature, so it suits H13, M2 and D2 tempered at 500 °C or above, not O1 tempered at 200 °C. Nitriding of H13 dies for die-casting; black oxide for storage.

Other steel series

Tool Steel — frequently asked

What is tool steel?

Tool steels are high-carbon (0.5–2.3 % C) steels alloyed with chromium, vanadium, tungsten and molybdenum to form hard carbides, hardened and tempered to 55–66 HRC for parts that cut, punch, form or wear. The AISI letters describe the job: A (air-hardening) and D (high-carbon high-chromium) for cold-work dies, O (oil-hardening) for small tools and gauges, S (shock-resisting) for punches and chisels, H (hot-work) for die-casting and forging dies, M and T (high-speed) for cutting edges that run hot.

Which grade of tool steel should I use?

A2 for general cold-work dies, punches and fixtures: air-hardens to 60–62 HRC with little distortion and a good balance of toughness and wear. D2 (1.2379, SKD11, Cr12MoV) when wear is the driver — 12 % chromium carbides give long die life at 58–62 HRC at the cost of toughness and grindability; DC53 is the tougher modern version. O1 (1.2510) for gauges, knives and one-off small tools that will be oil-quenched in-house. S7 for anything struck — chisels, shear blades, punches at 54–58 HRC — and as a tough general fixture steel. H13 (1.2344, SKD61) for die-casting dies, extrusion tooling, hot-forging and plastic molds at 44–52 HRC where the tool runs at 300–600 °C. M2 (W6Mo5Cr4V2, SKH51) for cutters, broaches and punches at 62–65 HRC; A11 / CPM 10V and CPM 3V are the powder-metallurgy grades for extreme wear or extreme toughness.

Which grade of tool steel is the strongest?

9Cr18Mo has the highest yield strength in the series at 1,900 MPa; Vanadis 4 Extra follows at 1,900 MPa. Values are for each grade's default condition.

Which grade of tool steel is easiest to machine?

A10 (machinability good, 68/100), then O6 (62/100).

Is tool steel heat-treatable?

Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.

D2 or A2?

A2 unless wear is the limiting factor. A2 (5 % Cr, 1 % C) is tougher, grinds and machines more easily, and distorts less in air-hardening — the general-purpose die steel at 60–62 HRC. D2 (12 % Cr, 1.5 % C) carries far more chromium carbide, so it lasts two to three times as long in abrasive blanking and forming but chips on impact and is harder to grind. If D2 chips, DC53 or CPM 3V give D2-class wear with much better toughness.

When is H13 the right choice over D2?

Whenever the tool runs hot. D2 loses its hardness above about 250 °C and cracks under thermal cycling; H13 (0.4 % C, 5 % Cr, 1.3 % Mo, 1 % V) holds 44–50 HRC to about 550 °C, resists heat checking and thermal fatigue, and tolerates water cooling — so it is the die-casting, extrusion and hot-forging steel, and also a tough plastic-mold steel at 48–52 HRC. At room temperature D2 outwears it several times over.