N690 produced by Böhler, is a stainless steel that shares some similarities with the well-known 440C, but with the addition of cobalt for improved performance.
D2 steel, on the other hand, is a high-carbon, high-chromium tool steel that, despite not being classified as stainless, has found widespread use in the knife industry.
A key difference between D2 and N690 steel lies in their corrosion resistance and ease of maintenance.
N690 stainless steel offers superior rust resistance compared to D2, making it more suitable for humid environments or for users who prefer lower maintenance knives.
Additionally, N690 is generally easier to sharpen than D2, which can be an important consideration for both manufacturers during production and end-users during maintenance.
Both steels offer compelling properties for knife makers and users, occupying a space between budget steels and premium options like M390.
N690 vs D2 Steel At A Glance
| Property | N690 Steel | D2 Steel |
|---|---|---|
| Hardness | 60 HRC | Up to 63 HRC |
| Toughness | Better than D2 | Lower (more brittle) |
| Ease of Sharpening | Easier to sharpen | More difficult |
| Corrosion Resistance | Better (stainless) | Good for non-stainless, but lower |
| Edge Retention | Good | Better than N690 |
Hardness
D2 knife steel generally achieves a higher maximum hardness than N690 steel.
D2 steel can reach hardness levels of up to 63 HRC, while N690 typically achieves a hardness of around 60 HRC.
This difference in maximum hardness is likely due to D2 higher carbon content (typically around 1.5%) compared to N690 (which has about 1.07% carbon).
The higher carbon content in D2 allows for the formation of more carbides, contributing to its increased hardness potential.
However, it’s worth noting that while D2 can achieve a higher peak hardness, N690 benefits from the addition of cobalt, which enhances its tempering resistance and secondary hardening characteristics.
This means that N690 may retain its hardness better at higher tempering temperatures compared to some other steels, even if its maximum hardness is lower than D2.
Toughness
N690 exhibits better toughness than D2, when comparing the toughness of N690 and D2 steels in knife applications.
This superior toughness in N690 is primarily attributed to its lower achievable maximum hardness (around 60 HRC compared to D2’s 63 HRC), which results in less brittleness.
The lower carbon content and different alloying elements in N690 contribute to its improved toughness.
D2, with its higher carbon content and larger carbides, tends to be more brittle and less tough. This difference in toughness affects knife performance significantly.
N690 knives will be more resistant to chipping and breaking under stress, making them more suitable for tasks involving lateral stress or impact.
On the other hand, D2 knives will be more prone to chipping or breaking if subjected to extreme lateral forces.
The improved toughness of N690 makes it a more versatile choice for general-purpose knives, especially those that might encounter varied or unpredictable use conditions.
However, it’s important to note that heat treatment and overall knife design also play crucial roles in the final toughness and performance of a knife, regardless of the steel type used.
Edge Retention
D2 steel outperforms N690 steel in edge retention and wear resistance.
D2 achieves better edge retention and wear resistance primarily due to its higher carbon content (around 1.5% compared to N690’s 1.07%) and larger volume of carbides.
The higher carbon content in D2 allows for the formation of more numerous and larger carbides, particularly chromium carbides, which significantly enhance its wear resistance.
This translates to superior edge retention in knives, as the blade is better able to resist abrasion and maintain its sharp edge during use.
The CATRA testing shows D2 steel to have better edge retention than N690 stainless steel.
Additionally, D2’s ability to achieve a higher maximum hardness (up to 63 HRC compared to N690’s 60 HRC) further contributes to its improved wear resistance and edge retention.
Knives made from D2 steel will typically maintain their sharp edge for longer periods of use, especially in demanding cutting tasks, compared to those made from N690.
Corrosion Resistance
N690 exhibits significantly better corrosion resistance compared to D2 carbon steel, primarily due to the difference in chromium content.
N690 is a stainless steel, containing approximately 17% chromium, which is well above the 12% threshold typically required for a steel to be considered stainless.
In contrast, D2 is a non-stainless steel, with a chromium content of around 12%.
While this amount of chromium in D2 does provide some corrosion resistance, it’s not enough to classify it as truly stainless.
The higher chromium content in N690 forms a more effective passive layer on the steel’s surface, providing superior protection against rust and corrosion.
Additionally, in D2, approximately half of its chromium is tied up in carbides, further reducing its effective corrosion resistance.
This difference significantly impacts knife performance in various environments.
N690 knives will maintain their appearance and integrity much better in humid or corrosive environments, requiring less maintenance to prevent rust.
D2 knives, while having some corrosion resistance, are more susceptible to rusting and will require more careful maintenance, especially in humid or marine environments.
Ease of Sharpening
N690 is easier to sharpen and grind compared to D2 steel, which has significant implications for knife maintenance and manufacturing.
This difference in ease of sharpening is primarily due to the steels’ composition and microstructure.
D2 steel, with its higher carbon content (around 1.5%) and larger volume of carbides, particularly chromium carbides, presents more challenges during sharpening.
These large, hard carbides in D2 can make the steel more abrasive on sharpening stones and require more time and effort to achieve a fine edge.
In contrast, N690, with its lower carbon content (about 1.07%) and more refined carbide structure, offers less resistance during sharpening.
Bohler N690 was developed for “better grinding,” which aligns with its superior sharpenability.
For knife users, this means that N690 blades can be more easily maintained and resharpened in the field or at home, requiring less time and skill to restore a sharp edge.
However, it’s important to note that while D2 is more challenging to sharpen, its superior edge retention means it may require less frequent sharpening overall.
Final Thoughts On N690 vs D2 Steel
In comparing N690 and D2 steels, both offer excellent performance for knife applications, but with distinct advantages.
From personal experience, I’ve found that knives made from both steels perform admirably in everyday use, with the differences being subtle in many cases.
However, for those new to knife steels, I would recommend N690 as a starting point.
Its stainless properties and easier maintenance make it more forgiving for users still developing their sharpening skills and maintenance routines.
D2, while exceptional in edge retention and wear resistance, demands more attention to prevent corrosion and requires more time and skill to sharpen effectively.
That said, experienced users who prioritize edge retention and don’t mind the extra maintenance might prefer D2.
Ultimately, the choice between N690 and D2 comes down to individual priorities – whether you value easier maintenance and corrosion resistance (N690) or superior edge retention and wear resistance (D2).
Both steels represent a significant step up from budget options, offering performance that will satisfy most users in a wide range of cutting tasks.