D2 Tool Steel
Also: AISI D2, UNS T30402, W.Nr. 1.2379, DIN 1.2379, X153CrMoV12, SKD11 (JIS, near), Böhler K110, Uddeholm Sverker 21, D-2, D2 cold work tool steel, D2 ground flat stock
D2 is the high-carbon, high-chromium cold work tool steel: top wear resistance for blanking dies, punches and slitter knives at 58-62 HRC.
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At a glance
| Density | 7.7 g/cm³ (0.278 lb/in³) |
|---|---|
| Tensile strength | About 750-850 MPa (110-125 ksi) annealed, estimated from hardness. Not a published property at 58-62 HRC, where D2 is rated by hardness and compressive strength. |
| Yield strength | n/a: tensile yield is not commonly published for hardened D2, which breaks with almost no plastic strain in tension. Compressive yield exceeds 2,000 MPa (290 ksi) at 58-62 HRC. |
| Hardness | 217-255 HB annealed; 58-62 HRC working hardness (about 62-64 HRC as quenched) |
| Elongation | Not meaningful at working hardness (near zero in tension); annealed stock saws, machines and straightens without trouble |
| Modulus of elasticity | 210 GPa (30.5 Msi) |
| Thermal | Solidus roughly 1,400 °C (2,550 °F); softens above its tempering temperature, about 200 °C (400 °F) for a low temper or 510 °C (950 °F) for a high temper; thermal conductivity ~20 W/m·K |
| Composition | Fe, 1.40-1.60% C, 11.0-13.0% Cr, 0.70-1.20% Mo, up to 1.10% V, 0.10-0.60% Mn, 0.10-0.60% Si |
Typical values, Annealed as stocked (217-255 HB); working hardness after an air or gas quench from about 1,010 °C (1,850 °F) and a double temper to 58-62 HRC. Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 40-50% of the W1 (1% carbon tool steel) benchmark annealed. The chromium carbides wear tools quickly: use carbide, rigid setups and steady feeds. Hardened D2 is ground, wire EDM cut, or hard milled slowly with coated carbide or CBN.
- WeldabilityPoor
- Repair welding only. The heat-affected zone air-hardens and cracks unless the part is preheated, to about 370-480 °C (700-900 °F) for annealed stock or just below the last tempering temperature for a hardened die, welded by TIG with a matching tool steel filler, cooled slowly and tempered. Not a fabrication steel.
- FormabilityPoor
- Not a forming steel: it is bought as bar, flat and plate and machined. Annealed stock can be straightened; hardened D2 cannot be bent at all.
- Corrosion resistanceFair
- About 12% chromium, but much of it is tied up in carbides, so D2 is not stainless. It stains less than A2 or O1 and still rusts in humid shops and wet service; oil it or coat it.
D2 is a cold work tool steel with about 1.5% carbon and 12% chromium. Much of that chromium combines with the carbon as hard chromium carbides, and that carbide volume is what gives D2 its wear resistance. It hardens in still air or a gas quench, moves little and predictably in heat treatment, and is the default steel for long-run blanking and piercing dies, trim dies, punches for thin stock, slitter and shear knives, thread rolling dies, gauges and wear parts.
It is bought annealed at 217-255 HB, machined, then hardened and tempered to 58-62 HRC. There are two tempering routes. A low temper around 200 °C (400 °F) gives 60-62 HRC and the most wear resistance. A high temper around 510-540 °C (950-1,000 °F) uses secondary hardening to reach 58-60 HRC with less retained austenite, better dimensional stability, and a part that tolerates wire EDM, nitriding and PVD coating without softening.
The price of that wear resistance is toughness and workability. D2 chips at sharp corners and cracks under heavy shock or thick stock, it is slow to machine and grind, and a low-tempered block can crack when it is wire-cut deeply. Despite the chromium it is not stainless. When chipping is the failure mode, A2 or S7 is the usual step; when D2 wears out too fast, M2 or a powder-metal cold work grade.
Heat treatment
Preheat at about 815 °C (1,500 °F), austenitize at 995-1,025 °C (1,825-1,875 °F) and soak, then cool in still air or a pressurized gas quench to about 50-65 °C (125-150 °F) and temper immediately, twice. Temper at 200-230 °C (400-450 °F) for 60-62 HRC, or at 510-540 °C (950-1,000 °F) for 58-60 HRC with secondary hardening and better stability. A sub-zero treatment between quench and temper cuts retained austenite for gauges. Harden in vacuum or a protective atmosphere to avoid a decarburized skin. Anneal at 870-900 °C (1,600-1,650 °F) with a slow furnace cool; stress relieve after rough machining at 650-675 °C (1,200-1,250 °F).
Tempers and conditions
- Annealed (217-255 HB), as stocked
- Hardened, low temper, 60-62 HRC
- Hardened, high temper, 58-60 HRC (secondary hardened)
- Precision ground and decarb-free stock (annealed)
Stock forms
- Round and flat bar
- Plate and saw-cut blocks
- Precision ground flat and square stock
- Decarb-free (DF) oversize flat bar
- Drill rod
- Forged rings and discs for rolls and slitter knives
Relative cost
Tier 3 of 5. Annealed bar and plate cost roughly 1.3-1.5x O1 and about 3x 4140 per pound. On a finished die, grinding and EDM time on hardened D2 usually costs more than the steel.
Typical applications
- Blanking, piercing and trim dies for long runs
- Punches for thin sheet and abrasive stock
- Slitter knives and shear blades for thin gauge
- Thread rolling and forming dies
- Gauges, wear plates and guides
- Mold inserts for glass-filled plastics
- Knife blades
Process compatibility
How D2 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| Wire EDM | ExcellentExcellent | The usual way to cut die openings in hardened D2. Temper high (510-540 °C) or stress relieve before deep cuts in big blocks, and skim-cut off the recast layer. Can D2 tool steel be wire EDM cut? |
| CNC Grinding | GoodGood | The standard finish after hardening; slow on the carbides, so use a friable or CBN wheel and plenty of coolant to avoid grinding burn and cracks. |
| Sinker EDM | GoodGood | Burns blind forms and cavities in hardened stock; stone or polish off the white layer and temper after heavy roughing. |
| CNC Machining | FairFair | Annealed, with carbide and rigid setups; leave grind stock. Hard milling at 58-62 HRC works with coated carbide or CBN but is slow. Can hardened D2 be machined? |
| Vacuum Heat Treating | ExcellentExcellent | Air hardening, so a nitrogen gas quench hardens it through and keeps the surface bright and decarb-free: the preferred route. |
| Heat Treating | GoodGood | Harden in a protective atmosphere or a stainless foil wrap, preheat, soak at about 1,010 °C and temper twice; open-air hardening leaves a soft, decarburized skin. |
| Stress Relieving | GoodGood | At 650-675 °C (1,200-1,250 °F) after rough machining, so long or unbalanced parts move less in hardening. |
| Nitriding | GoodGood | Only on D2 tempered high, at or above the nitriding temperature; gives a thin, very hard case against galling. Low-tempered D2 would soften. |
| Hard Chrome Plating | FairFair | Used on forming tools against galling; bake for hydrogen right after plating and expect build-up on edges. Nitriding or PVD coatings usually do the job better. |
| Black Oxide | FairFair | The chromium resists a standard hot bath and the colour can come out patchy; ask for a process meant for high-chromium steels, or just oil the part. |
| Waterjet Cutting | GoodGood | Profiles thick plate blanks in any condition with no heat-affected zone; leave stock to machine off the taper. |
| Laser Cutting | FairFair | Thin annealed plate cuts, but the edge air-hardens into brittle martensite and can crack; grind or machine it off. Tool shops usually saw, waterjet or wire-cut D2. |
| Welding | PoorPoor | Repair only: preheat about 370-480 °C (700-900 °F) on annealed stock, matching filler, slow cool, then temper. The HAZ cracks if welded cold. |
| Induction Hardening | Not recommendedNot recommended | D2 needs a long soak near 1,010 °C to dissolve its chromium carbides; a fast induction cycle leaves it under-hardened or cracked. Through-harden the whole part. |
Compare D2
Design and sourcing tips
- Call out the grade, the hardness and the temper route: "D2, 58-60 HRC, temper 510 °C (950 °F) min" when the part will be wire-cut, nitrided or PVD coated; "D2, 60-62 HRC" for the most wear when it will not.
- Radius the corners of die openings and punch profiles wherever the part allows; sharp corners at 60 HRC start chips and quench cracks.
- Leave about 0.2-0.4 mm (0.008-0.015") per side for finish grinding after hardening, more on long or thin parts; D2 grows slightly and predictably.
- Pick A2 or S7 instead when the tool sees heavy shock, thick stock or side loads: D2 wears longest but chips first.
- Specify vacuum hardening or decarb-free stock for gauges and wear faces; D2 hardened in open air keeps a soft outer skin.
- After wire or sinker EDM on a hardened part, ask for a temper about 25 °C (50 °F) below the last tempering temperature to relieve the recast layer.
Frequently asked questions
- Can D2 be welded?
- Only as a repair, not for fabrication. The heat-affected zone air-hardens and cracks unless the part is preheated, to about 370-480 °C (700-900 °F) for annealed stock or just below the last tempering temperature for a hardened die, welded by TIG with a matching D2-type filler, kept hot through the weld, cooled slowly and then tempered. Badly damaged dies are often annealed, welded and re-hardened. Expect the repaired area to differ slightly in hardness from the base metal.
- D2 vs A2: which is tougher?
- A2. It carries about 1% carbon and 5% chromium against about 1.5% and 12% in D2, so it has far less carbide and noticeably better impact toughness at the same hardness. D2 has markedly better abrasive wear resistance. Choose D2 for long runs on thin, abrasive stock and A2 for thicker stock, heavier shock, or wherever a D2 tool has been chipping.
- Is D2 stainless steel?
- No. D2 carries 11-13% chromium, close to the stainless threshold, but much of it is locked up in chromium carbides, so the matrix does not form a reliable passive film. It resists staining better than O1 or A2, and it is sometimes sold as "semi-stainless" for knives, but it rusts in wet or humid service. For a hardened tool steel that resists corrosion, look at 440C.
- How hard is D2 tool steel?
- Annealed, as bought, it is about 217-255 HB, soft enough to machine. Hardened and tempered it is used at 58-62 HRC: 60-62 HRC with a low temper around 200 °C (400 °F) for the most wear, or 58-60 HRC with a high temper around 510-540 °C (950-1,000 °F) for stability and compatibility with EDM and coatings. As quenched it reaches about 62-64 HRC.
- Is D2 good for knives?
- For edge retention, yes: the chromium carbides hold a working edge a long time and the steel resists staining better than carbon steel. The same coarse carbides make it harder to sharpen, limit how fine the edge can be and lower toughness, so thin D2 edges chip under prying or impact. It suits folding and utility knives at about 58-61 HRC; choppers and hard-use blades do better in a tougher steel.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A681 (chemistry and annealed hardness limits)
- Producer data sheets: Crucible D2, Böhler K110, Uddeholm Sverker 21
- ASM Handbook Vol. 4, Heat Treating (tool steel hardening and tempering)
- Roberts, Krauss and Kennedy, Tool Steels, 5th ed. (ASM International)
