There’s no definitive answer when comparing steel types, like O1 vs D2, as to which is the ‘best steel’. Instead, there are subjective answers in which one kind of steel may be less prone to rusting, for example, or another grade may be easier to sharpen. Comparing O1 and D2 tool steels means studying the qualities of each; however, deciding on the best type ultimately depends on the intended use.
In this article, we will discuss the topic O1 vs D2 tool steel, by comparing the attributes of both to help you make an informed decision regarding your next project.
What is O1 Tool Steel?
The O1 tool steel is a cold-work steel with high levels of carbon in its composition. It is part of the ‘O’ group of steels, which means it is oil-hardening. This group of steels contains O2, O6, O7 and O1 tool steels.
O1 is a general-purpose steel suitable for various applications. It has high machinability and requires lower hardening temperatures than most other grades. As well as this, the O1 grade features high levels of wear resistance and toughness, all for a relatively affordable price (compared to alternative grades). This is what makes it such a popular steel grade in the tool making community.
Chemical Composition of O1 Tool Steel
| Element | Content (%) |
| C | 0.85 – 1.00 |
| Mn | 1.00 – 1.40 |
| Si | 0.50 |
| Cr | 0.40 – 0.60 |
| Ni | 0.30 |
| W | 0.40 – 0.60 |
| V | 0.30 |
| Cu | 0.25 |
| P | 0.03 |
| S | 0.03 |
Mechanical Properties of O1 Tool Steel
| Mechanical Properties | Metric | Imperial |
| Hardness, Brinell (soft annealed) | 190 | 190 |
| Hardness, Rockwell C (tempering temp 149-649°C) | 34.0-64.0 | 34.0-64.0 |
| Elastic modulus (hardened to 62 HRC) | 193 GPa | 28000 ksi |
| Elastic modulus (at 399°C, hardened to 62 HRC ) | 172 GPa | 25000 ksi |
| Elastic modulus (at 191°C, hardened to 62 HRC) | 186 GPa | 27000 ksi |
| Compressive yield strength (0.2%, hardened to 50 HRC) | 1350 MPa | 196000 psi |
| Compressive yield strength (0.2%, hardened to 55 HRC) | 1800 MPa | 261000 psi |
| Compressive yield strength (0.2%, hardened to 60 HRC) | 2150 MPa | 312000 psi |
| Compressive yield strength (0.2%, hardened to 62 HRC) | 2200 MPa | 319000 psi |
What is D2 Tool Steel?
Like O1, D2 is also a cold-work, high carbon tool steel. However, instead of being oil-hardened, D2 is an air-hardened tool steel. The high levels of carbon, and chrome, in the steel’s composition result in extremely high wear resistance levels.
D2 is a very tough tool steel with high levels of wear resistance; however, these qualities come at the expense of other attributes such as machinability. What it lacks in machinability, it makes up for in its hardening ability. This makes D2 tool steel extremely resistant to chipping and cracking, meaning it’s ideal for tools that require a long life with minimal wear and tear.
Chemical Composition of D2 Tool Steel
| Element | Content (%) |
| C | 1.40 – 1.60 |
| Mn | 0.60 |
| Si | 0.60 |
| Co | 1.00 |
| Cr | 11.00 – 13.00 |
| Mo | 0.70 – 1.20 |
| V | 1.10 |
| P | 0.03 |
| Ni | 0.30 |
| Cu | 0.25 |
| S | 0.03 |
Mechanical Properties of D2 Tool Steel
| Mechanical Properties | Metric | Imperial |
| Hardness, Knoop | 769 | 769 |
| Hardness, Rockwell C | 62 | 62 |
| Hardness, Vickers | 748 | 748 |
| Elastic modulus | 190-210 GPa | 27557-30457 ksi |
Applications of O1 Steel
O1 steel has great qualities across the board whilst still being a more affordable tool steel. This means it’s used for a wide range of applications, especially where the reasonable cost outweighs the qualities and the need for a specialised grade is lessened.
O1 tool steel is commonly used for the following purposes:
- Gauges
- Jigs
- Cutters
- Stamps
- Shims
- Levers
- Saws
- Guides
- Fixtures
- Machine Parts
- Punches
- Dies
- Blanking Dies
- Forming Dies
- Lamination Dies
- Moulding Dies
- Trim Dies
- Screw Dies
- Swaging Dies
- Draw Dies
O1 tool steel is also commonly used in the Knife producing industry, and even more so by DIY Knifemakers, as it has the ability to produce a strong, sharp edge, it can be sharpened relatively easily – although it will rarely need sharpening as it won’t dull easily due to its high wear resistance.
When it comes to knifemaking, the intended use and personal preference ultimately determine the most appropriate tool steel. Many in the knifemaking community prefer O1 vs D2 tool steel for their knives, as it is incredibly durable and holds a sharp edge well.
However, it’s important to note that, compared to D2, O1 will require a little more maintenance when used. Its chromium content isn’t as high as D2, which may result in some rusting and corrosion over time.
Of course, this can be prevented with proper maintenance, e.g. regular oiling of the blade. But, again, this is up to personal preference; if you are looking for a knife that will last a long time as long as it is carefully maintained, then O1 is a suitable material to use.
Applications of D2 Steel
D2 tool steel is also used across many industries for a wide range of applications. With similar properties to O1, it’s no wonder that D2 is also used for the same sort of purposes. Although the increased wear resistance and hardness levels mean it is actually suitable for more unique purposes than the all-rounder O1.
Common applications of D2 steel include:
- Gauges
- Shear Blades
- Machine Parts
- Tyre Shredders
- Scrap Choppers
- Punches
- Slitting Cutters
- Burnishing Tools
- Forming Rolls
- Punches
- Dies
- Blanking Dies
- Forming Dies
- Trim Dies
- Lamination Dies
- Thread Rolling Dies
- Drawing Dies
- Rotary Cutting Dies
- Bending Dies
- Extrusion Dies
- Stamping Dies
The list goes on!
When it comes to knives, D2 is a common choice for enthusiasts as it has excellent corrosion resistance, so it won’t go rusty quickly if you’re using it out in the elements. However, the debate surrounding O1 vs D2 tool steel is continuous; ultimately, it depends on your preference and its intended use.
Many knifemakers argue D2 retains its edge better than O1, whilst others argue that the edge in question isn’t as sharp with D2 steel. Furthermore, with its increased hardness levels, D2 can become brittle if not properly maintained – an issue not commonly associated with O1 steel.
O1 vs D2: Choosing a Tool Steel
Without sounding like a broken record, there really is no right or wrong answer when it comes to choosing the best tool steel for your job. The differences between O1 and D2 tool steels are not hugely significant; as shown above, both steel grades are used for many of the same applications.
The best way to determine the most suitable steel grade for your intended purpose is to carefully think about the qualities you require from your material – whether that be great edge retention or superior durability, and go from there.
Both O1 and D2 are affordable yet high-quality tool steel grades that will work for a range of applications. When purchasing steel, it’s essential to find a supplier with years of experience and outstanding quality products.
At Sheffield Gauge Plate, we stock both O1 and D2 tool steels and a wide range of other grades in all standard sizes. Contact us today to discuss your project with one of our friendly steel experts, who will help you find the correct grades and sizes.