N690 vs M390 Steel

N690, manufactured by Böhler, is a well-regarded conventional stainless steel often found in budget to mid-range knives.

On the other hand, M390 also produced by Böhler, is a premium powder metallurgy steel that has gained a reputation as one of the best all-around knife steels available.

The key differences between these two steels lie in their edge retention and corrosion resistance.

M390, with its advanced powder metallurgy production process and high alloy content, significantly outperforms N690 in both these aspects.

This makes M390 a popular choice for high-end knives where performance is paramount, while N690 remains a solid option for budget-conscious buyers or those who prioritize ease of maintenance

N690 vs M390 Steel At A Glance

Hardness

M390 steel can achieve significantly higher hardness levels compared to N690 steel.

While N690 steel typically reaches a hardness of 60 HRC, M390 steel is capable of attaining hardness levels up to around 66 HRC.

This difference in maximum hardness is substantial, with M390 having a 6 HRC point advantage over N690.

According to Bohler the recommended or aim hardness for knife steel for N690 steel is 55-60 HRC while for M390 steel hardness range is 56-61 HRC.

The higher potential hardness of M390 is likely due to its composition and microstructure, which includes a high carbide volume (about 22%) and the presence of vanadium carbides.

In contrast, N690 is described as being similar to 440C but with added cobalt and a small increase in molybdenum, which primarily affects its tempering resistance rather than its maximum attainable hardness. 

Toughness

M390 despite its high hardness potential, can achieve comparable or slightly higher toughness than N690 at their recommended hardness ranges of around 60 HRC.

This might seem counterintuitive given M390’s higher carbide content, which typically reduces toughness.

However, M390 advanced powder metallurgy production process contributes to its higher toughness.

For reference purpose the toughness levels of M390 and N690 steel are comparable to 440C stainless steel.

For knife applications, this means that M390 can offer excellent edge retention and wear resistance without significantly compromising on impact resistance compared to N690.

N690, with its cobalt addition, has good tempering resistance but doesn’t necessarily translate to superior toughness. 

Both steels can perform well in knives, but M390’s slightly higher toughness at comparable hardness levels may give it an edge in applications where impact resistance is crucial.

However, it’s essential to note that proper heat treatment is critical for both steels to achieve optimal toughness particularly for M390.

For M390 where excessive austenitizing temperatures can lead to retained austenite and potentially brittle behavior. 

Edge Retention

According to the Bohler CATRA test results, M390 steel significantly outperforms N690 in terms of edge retention and wear resistance.

The Total Cards Cut (TCC) score, which measures these properties, shows M390 achieving 958.6 at a hardness of 61+ HRC, while N690 scores 635.1 at a similar hardness.

This represents a substantial difference, with M390 cutting over 40% more cards than N690 in the standardized test. 

The superior edge retention of M390 is due to its high carbide content and advanced powder metallurgy production process, resulting in a fine, uniform microstructure.

M390’s exceptional performance can be attributed to its high carbide content, particularly its chromium carbides (about 18%) and vanadium carbides (2.5%), as well as its overall carbide volume of approximately 22%.

These carbides, combined with M390’s fine powder metallurgy microstructure, contribute to its outstanding wear resistance. 

For knife applications, this translates to M390 maintaining its cutting ability for much longer periods of use compared to N690. 

Knives made with M390 would require less frequent sharpening and perform better in demanding cutting tasks over extended periods.

While N690 knife steel is still a respectable performer, particularly among conventional stainless steels, it falls significantly short of M390 knife steel capabilities in this regard. 

The stark difference in wear resistance suggests that M390 would be the preferred choice for high-performance cutting tools where maintaining a sharp edge over time is crucial.

Corrosion Resistance 

M390 steel exhibits superior corrosion resistance compared to N690, making it a more suitable choice for environments where rust and oxidation are significant concerns.

This enhanced corrosion resistance in M390 is primarily due to its higher chromium content and the presence of additional alloying elements.

M390 contains about 20% chromium, which is significantly higher than N690’s 17% chromium content.

Additionally, M390 benefits from a higher molybdenum content, which further improves its corrosion resistance.

The high “chromium in solution” in M390, combined with its molybdenum and nitrogen content, contributes to its excellent performance in corrosive environments.

M390 knives will be more resistant to rust and staining, particularly in harsh conditions like marine environments or when exposed to corrosive substances. 

While N690 is still considered a corrosion-resistant stainless steel and performs adequately in many situations, it may be more prone to developing rust or discolouration compared to M390, especially in more aggressive environments.

For knife users, this translates to M390 requiring less maintenance and being more forgiving in terms of care and storage.

Ease of Sharpening

N690 is easier to sharpen than M390 steel, this difference in ease of sharpening is primarily due to the steel composition and microstructure.

N690, with its lower carbide content and smaller carbide size, offers less resistance to abrasives during the sharpening process.

In contrast, M390 steel high carbide volume (about 22%) and larger chromium carbides make it more challenging to grind and sharpen. 

For knife users, this means that maintaining a sharp edge on an N690 blade requires less time and effort compared to M390.

N690 knives can be quickly touched up with standard sharpening tools, making them more user-friendly for those who prefer to maintain their own blades. 

M390, while more difficult to sharpen, retains its edge longer, potentially offsetting the increased sharpening effort. 

Final Thoughts on N690 vs M390 Steel

In conclusion, while both N690 and M390 have their merits, M390 emerges as the superior choice for most high-performance knife applications due to its outstanding corrosion resistance and unparalleled edge retention capabilities.

Its powder metallurgy construction and high alloy content give it a significant edge in demanding situations where long-lasting sharpness and rust resistance are crucial.

However, this doesn’t mean N690 is without its virtues. I find N690 to be a great budget option, particularly for kitchen knives that require frequent sharpening.

Its easier maintenance and lower cost make it an attractive choice for everyday users who don’t need the extreme performance of M390.

For those seeking the absolute best performance and willing to invest in premium steel, M390 is hard to beat. 

On the other hand, if you’re looking for a reliable, corrosion-resistant steel that’s cheap and simpler to maintain, N690 remains an excellent choice.