Guide
A2 vs D2 tool steel: which one should a wear part or fixture be made from?
A2 vs D2 tool steel is the choice between a medium-alloy, air-hardening cold work steel with a good balance of wear and chipping resistance (A2), and a high-carbon, high-chromium steel with much better abrasive wear resistance but less toughness (D2). Choose D2 for parts that mainly see sliding or abrasive wear without impact; choose A2 for parts that also see shock, edge loading or thin sections that might chip or crack.
By Saola Manufacturing engineering team · Published · Updated
On this page
What is the difference between A2 and D2 in composition?
D2 carries roughly twice the chromium and more carbon than A2, which gives it a large volume of hard chromium carbides; A2 has less carbide and therefore more toughness. Both are air-hardening cold work steels covered as a family by ASTM A681.
Steelmaker Uddeholm’s datasheets give the typical analyses: its Rigor grade (AISI A2, W.-Nr. 1.2363) is about 1.0% carbon, 5.3% chromium, 1.1% molybdenum and 0.2% vanadium, and its Sverker 21 grade (AISI D2, W.-Nr. 1.2379) is about 1.55% carbon, 11.3% chromium, 0.8% molybdenum and 0.8% vanadium. The US purchasing specification for wrought alloy tool steels is ASTM A681, which covers bar, plate, sheet, strip, rod, wire and forgings normally made into tools, dies or fixtures.
The D2 datasheet describes the steel as having “very good abrasive wear resistance but with rather limited cracking resistance,” and the A2 datasheet places that grade between the high-chromium steels and oil-hardening O1, with “an excellent combination of wear and chipping resistance.” That one sentence is the whole selection logic: D2 for wear, A2 when wear and toughness both matter.
| Property | A2 (Uddeholm Rigor) | D2 (Uddeholm Sverker 21) |
|---|---|---|
| Carbon, typical % | 1.0 | 1.55 |
| Chromium, typical % | 5.3 | 11.3 |
| Molybdenum, typical % | 1.1 | 0.8 |
| Vanadium, typical % | 0.2 | 0.8 |
| Delivery condition | Soft annealed to approx. 215 HB | Soft annealed to approx. 210 HB |
| Hardness for gauges, guide rails, bushes, sleeves | 58–62 HRC | 58–62 HRC |
| Abrasive wear resistance | Good | Very good |
| Chipping and cracking resistance | Better | Rather limited |
| Machining and grinding in the annealed condition | Described as excellent | Harder going, more carbide |
Which one lasts longer on a wear part?
On pure sliding or abrasive wear, such as guide rails, wear strips, bushings and nozzles, D2 usually lasts longer at the same hardness because of its larger carbide volume. Once impact, edge loading or bending enters the picture, A2 tends to win because a chipped D2 edge ends its life sooner than wear would.
The two datasheets list overlapping applications at similar hardness: both name gauges, measuring tools, guide rails, bushes and sleeves at 58–62 HRC, typical working hardness for each grade. The difference is in where they recommend going further. Uddeholm recommends its D2 grade for applications where abrasive wear is dominant and the risk of chipping or cracking is not so high, and notes that because D2 is the bulk cold work grade, it is often used by routine where its profile is not appropriate.
A useful rule is to look at how a worn-out part from the current design failed. A part that is polished, grooved or worn undersize is a wear failure, and D2 is the natural upgrade. A part that is chipped, cracked at a corner or broken at a thin section is a toughness failure, and moving to D2 makes it worse; A2, or a tougher grade, is the better direction.
Which tool steel is better for fixtures, locators and gauges?
For hardened locators, rest pads, nest pins and gauge components, either grade works; D2 is chosen for high-cycle abrasive contact and A2 for parts with thin walls, sharp corners or knocks during loading. For fixture bodies and plates that are not hardened, neither is necessary.
Most of a fixture is not tool steel at all. Base plates and bodies are typically aluminum or low-carbon steel, and only the contact points are hardened. Hardened contact points must stay dimensionally stable after heat treatment, which both grades handle well as air-hardening steels; the Uddeholm D2 datasheet lists high stability in hardening among its properties, and the A2 datasheet lists high stability after hardening.
If a locator gets knocked by parts being loaded, or has a thin flange, A2 is the safer choice. If it guides a sliding part all day in an abrasive environment, such as cast parts with sand residue or ground parts with grit, D2 earns its place. Our checking fixture guide covers the gauge side of fixture design.
How are A2 and D2 parts machined and heat treated?
Both are rough machined in the soft annealed condition, stress relieved if needed, hardened and tempered, then finished by grinding or EDM. The drawing should give the final hardness range and mark the surfaces that are ground after heat treatment.
The A2 datasheet recommends a stress relief after rough machining before hardening, and both steels harden in air or protective gas, which keeps distortion lower than in oil-quenched grades. Machining allowance must cover the small size change in hardening; both datasheets publish dimensional change data, so a supplier can plan grinding stock. Hardened D2 is hard on grinding wheels because of its carbides, and Uddeholm publishes separate grinding and EDM guidance for its tool steels, which is a hint that both operations need care.
On the drawing, write the steel, the hardness range, and which faces are finished after hardening. A common practice is to mark ground faces with a surface texture and leave other faces as machined before heat treatment. If wire or sinker EDM will cut hardened features, ask the supplier how the recast layer is removed on functional edges.
How should the drawing and RFQ call out A2 or D2?
Name the grade by AISI designation or the European number, give a hardness range in HRC, and add the heat treatment and certification you need. “Tool steel, hardened” on its own leaves too much open.
- Material. “TOOL STEEL AISI D2 (W.-NR. 1.2379) PER ASTM A681” or the A2 equivalent (1.2363).
- Hardness. A range rather than a single value, and where it is measured.
- Heat treatment. Harden and temper; add a sub-zero treatment or multiple tempers only if dimensional stability needs it.
- Finished surfaces. Which faces are ground after hardening, with surface texture.
- Certificates. Material certificate and hardness test record.
- Coatings. If a PVD coating or nitriding is planned, say so, because tempering temperature must be compatible.
When is neither A2 nor D2 the right answer?
When the part sees heavy shock, use a shock-resisting steel such as S7; when wear is extreme, a powder-metallurgy tool steel or carbide; when it is a low-load wear part, a case-hardened or through-hardened alloy steel may be enough and cheaper to machine.
A2 and D2 sit in the middle of the cold work range, which is why they are so common. The D2 datasheet itself points users toward other grades when its profile does not fit. For a buyer, the practical point is that the steel follows the failure mode and the volume: a low-volume bushing in a clean environment does not need D2, and a high-cycle wear strip in abrasive service may outgrow it.
How does Saola handle tool steel parts?
Tool steels are not on the material lists of the capability pages, so the grade, the hardening route and the hardness range are confirmed at drawing review. Grinding and EDM are among the processes at the lead CNC plant, and a hardness tester is part of the inspection equipment.
Turned and milled parts are made on the CNC turning and CNC milling lines at the lead plant, T.K Viet Nam Precision. Hardening of tool steel is not listed on those pages either, so the review will say how it is arranged for your part. Material certification is available on request, and ISO 9001 certification is in progress, not held, as the quality page explains. Send the drawing with the grade and hardness through the quote form.
Frequently asked
Is D2 stainless steel?
No. D2 has high chromium but much of it is tied up in carbides, so it resists staining better than A2 but is not a stainless steel and will rust in wet service.
Is A2 easier to machine than D2?
Yes, in the annealed condition A2 is generally easier to machine and grind, which Uddeholm’s datasheet describes as excellent machining and grinding properties.
Can D2 be welded for repair?
It can, with preheat and the right filler, but it is crack-prone. Treat welding of hardened D2 as a specialist repair, not routine.
What hardness should a D2 wear strip be?
Wear parts are typically run in the high 50s to low 60s HRC. Give a range on the drawing and let the supplier confirm it against the heat treatment.
What are the European equivalents?
A2 corresponds to W.-Nr. 1.2363 and D2 to W.-Nr. 1.2379, per the steelmaker datasheets.
Sources
- Uddeholm Rigor (AISI A2) datasheet, edition 10, Uddeholms AB, 2019
- Uddeholm Sverker 21 (AISI D2) datasheet, edition 13, Uddeholms AB, 2019
- ASTM A681-24, Standard Specification for Tool Steels Alloy, ASTM International, 2024