A2 Steel vs D2 Steel: Key Differences and Best Uses

Tool steels are well named, as they’re a family of low-carbon steel alloys developed and optimised for use in tools. One of the most important, but often unsung, advances of the industrial age was the rapid development of machine tools – ‘machines that could make machines’. Tool steel enabled the creation, then the mass production, of precise parts from highly durable materials at increasing rates.

Today, two of the most common tool steels used in industries around the world are graded as A2 and D2. What do we mean when we talk about A2 steel vs D2 steel? What are the properties of D2 vs A2 steel, and what uses are these important metals put to?

Rapid Metals includes tool steels in our wide range of metals and metal products. As one of the UK’s foremost metal suppliers, we can answer these questions about A2 steel vs D2 steel. Read – and enjoy – our blog to learn more.

Grading Tool Steel

The terms A2 Steel and D2 steel both refer to the standardised way of grading and describing tool steels. The system was developed by the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE), and groups tool steels based on the characteristics of their material and their basic applications.

There are six common categories of tool steel under the AISI/SAE system, each represented by a letter: water-hardening (W), oil-hardening (O), air-hardening (A), high carbon-chromium (D), shock-resisting (S) and hot-working (H). There are other specialist types such as high-speed (T and M), low-alloy (L) and carbon tungsten (F).

So already we can see that when we’re looking at A2 steel vs D2 steel we’re comparing an air-hardening tool steel and a high carbon-chromium type. They are notably different in terms of their composition as well – D2 has slightly more carbon and more than double the chromium content as A2.

With different classifications, they’re certain to have different characteristics and uses.

Within each group, the number refers to a specific variety of tool steel of that broad type – while there are different varieties of air-hardened tool steels, all their classifications will start with ‘A’, for instance.

The Difference Between A2 Steel vs D2 Steel

So if A2 tool steel and D2 tool steel are different enough to be given different classifications, what does this mean in the real world?

Fundamentally, all the metallurgical, chemical and physical differences of A2 steel vs D2 steel come down to this: A2 offers greater toughness but reduced hardness when compared to D2 tool steel.

In everyday speech, toughness and hardness are virtually synonyms, but they have very specific and vitally different meanings when discussing the property of materials.

Toughness is the material’s ability to absorb energy, deform and be shaped without breaking. Hardness is the material’s ability to withstand localised surface forces that cause indentation, scratching and surface wear.

For example, pure copper has high toughness but low hardness – it can be rolled, folded, shaped and drawn without breaking, but is easily scratched and wears quickly. A ceramic plate is the opposite – it resists scratching and wear very well but is brittle and will break under impact or high force.

When considered across the whole range of available materials (or even all the different types of metal) all tool steels have high hardness because this is what gives them their ability to retain a sharp, precise cutting edge for tool work.

But within the world of tool steels, and considering A2 steel vs D2 steel, A2 steel is tougher but softer than D2 steel.

The Properties of A2 vs D2 Tool Steel

The different alloy compositions and treatments that give A2 and D2 tool steel their respective hardness and toughness also give them differing properties in other ways:

1) Machineability: With lower hardness but higher toughness, A2 tool steel has better machining properties, being more easily cut to precise and complex shapes and resisting cracking and impact damage when being worked.

2) Wear Resistance: D2 tool steel’s superior hardness gives it better resistance to abrasive wear and means that it retains edges and profiles extremely well.

3) Temperature Resistance: D2 tool steel has slightly better performance in high temperatures, retaining its specified hardness up to around 480 deg. C (900 deg. F), while A2 tool steel begins to soften at around 425 deg. C (800 deg. F).

The Uses of A2 vs D2 Tool Steel

With higher toughness and better machineability, but less wear and abrasion resistance, A2 tool steel is suitable for many tooling applications where high speeds or heavy cutting actions are not required.

These uses typically include dies for stamping, forming, trimming and punching. A2 tool steel is also used for blanking tools and shear blades. It can be a good choice for making measuring gauges (tools for determining clearances and sizes rather than instruments), as these functions need accuracy and precision but do not impose a lot of impact or abrasive stress.

By contrast, with superior hardness giving excellent wear resistance and good temperature control, D2 tool steel is ideal for cutting tools such as punches, saw blades and drill bits. It can also be used for making extrusion tooling, forging tools and various types of plastic mould. The hard-wearing properties and good dimensional stability of D2 tool steel also means that its uses can go beyond tools themselves, and it can also be used in the making of mechanical components such as gears, bearings and shafts.

D2 Tool Steel from Rapid Metals

With D2 tool steel being one of the most versatile grades of tool steel, it should be no surprise that Rapid Metals includes it in our range of tool steels. We can supply D2 tool steel as round bar, in a range of popular metric or Imperial diameters and cut to the length you require. We can also supply D2 tool steel as steel block, which you can order to any length, width and height as needed.

Although A2 tool steel isn’t part of our standard range in our online store, if you need it please do contact our team. We can work with our network of suppliers and provide a quote – we aim to please, whatever the size or scope of the order.