In the world of knife-making, steel selection plays a crucial role in determining the performance, durability, and overall value of a blade. Among the wide array of steel options available, M390 and N690 stand out as two high-performance materials, each with its unique set of characteristics.
Both steels are produced by the renowned Austrian company Böhler-Uddeholm, but they cater to different needs and applications.
M390 is often considered a “super steel” due to its exceptional wear resistance, edge retention, and corrosion resistance, making it a favorite for premium knives. On the other hand, N690 is known for its balanced properties, offering good toughness, corrosion resistance, and ease of sharpening at a more affordable price point.
This article will delve into the scientific data behind these steels, comparing them across various measurable properties such as chemical composition, edge retention, toughness, hardness, and corrosion resistance. Additionally, we will explore their manufacturing processes, heat treatment requirements, and real-world performance to help you make an informed choice.
Composition Analysis
The chemical composition of a steel greatly influences its properties such as hardness, toughness, and corrosion resistance. Below is a comparison of the elemental makeup of M390 and N690:
| Element | M390 (%) | N690 (%) |
|---|---|---|
| Carbon (C) | 1.90 | 1.08 |
| Chromium (Cr) | 20.00 | 17.00 |
| Molybdenum (Mo) | 1.00 | 1.10 |
| Vanadium (V) | 4.00 | 0.10 |
| Tungsten (W) | 0.60 | – |
| Cobalt (Co) | – | 1.50 |
| Manganese (Mn) | 0.30 | 0.40 |
| Silicon (Si) | 0.70 | 0.40 |
Key Alloying Elements:
- M390: The high chromium content (20%) provides excellent corrosion resistance, while the significant vanadium content (4%) enhances wear resistance through the formation of hard vanadium carbides.
- N690: With 17% chromium and added cobalt (1.5%), N690 offers good corrosion resistance and edge stability but lacks the extreme wear resistance provided by M390’s higher vanadium content.
Performance Metrics
Edge Retention
Edge retention is a critical factor for knife users who want their blades to stay sharp over extended periods without frequent sharpening.
- M390: Known for its exceptional edge retention due to its high vanadium carbide content and fine grain structure from powder metallurgy production. In CATRA tests, M390 scores around 950-1000 TCC (Total Card Cut), placing it among the top performers in terms of edge longevity[2][3].
- N690: While N690 offers decent edge retention, it falls short compared to M390 due to its lower vanadium content and coarser grain structure from conventional production methods. CATRA results for N690 typically range between 600-650 TCC, making it more suitable for applications where ease of sharpening is prioritized[1].
Toughness
Toughness refers to a steel’s ability to resist chipping or breaking under stress.
- M390: Despite its high hardness, M390 offers moderate toughness but can be prone to chipping in extreme conditions due to its high carbide volume[2]. It performs well in controlled environments but may not be ideal for heavy-duty tasks like batoning or chopping.
- N690: With a more balanced composition that includes cobalt and molybdenum, N690 exhibits better toughness than M390[1]. It is less likely to chip under impact, making it suitable for outdoor knives that encounter rough use.
Corrosion Resistance
Both steels are classified as stainless due to their high chromium content.
- M390: With 20% chromium and clean powder metallurgy production, M390 offers superior corrosion resistance even in harsh environments like saltwater exposure[3]. It is highly resistant to rusting and staining.
- N690: N690 also provides excellent corrosion resistance with its 17% chromium content but falls slightly behind M390 in extreme conditions[1]. However, it still performs well in humid or wet environments.
Hardness Range
Hardness is measured on the Rockwell C scale (HRC), which indicates how hard a steel can become after heat treatment.
- M390: Typically hardened between 60-62 HRC, M390 achieves high hardness levels that contribute to its outstanding wear resistance[2].
- N690: N690 generally reaches hardness levels around 58-60 HRC, offering a good balance between hardness and toughness[1].
Heat Treatment Considerations
Heat treatment plays a pivotal role in maximizing the performance of both steels.
Optimal Heat Treatment Parameters:
- M390:
- Austenitizing: Heat to around 1180°C (2156°F).
- Quenching: Rapid cooling in oil or air.
- Tempering: Typically done at around 180°C to 200°C (356°F to 392°F) for optimal hardness without sacrificing too much toughness[3]. The precise control required during heat treatment makes M390 more challenging to process but results in superior performance when done correctly.
- N690:
- Austenitizing: Heat to approximately 1050°C (1922°F).
- Quenching: Usually quenched in oil or air.
- Tempering: Performed at around 175°C to 225°C (347°F to 437°F)[1]. N690’s heat treatment is generally easier to manage compared to M390 due to its simpler alloying elements.
Real-World Performance
Edge Stability
Edge stability refers to how well a blade maintains its geometry during use without deforming or chipping.
- M390: Offers excellent edge stability thanks to its fine grain structure and high hardness but may be prone to micro-chipping under heavy loads.
- N690: Provides better edge stability under impact or lateral forces due to its higher toughness but sacrifices some edge retention in comparison[4].
Sharpening Behavior
Ease of sharpening is an important consideration for users who maintain their knives regularly.
- M390: Due to its high hardness and wear resistance, M390 can be difficult to sharpen without specialized equipment such as diamond stones[2].
- N690: Easier to sharpen than M390 using standard sharpening tools like ceramic or whetstones[1]. This makes it more user-friendly for those who prefer low-maintenance knives.
Wear Patterns
Wear patterns refer to how evenly or unevenly a blade wears down over time with regular use.
- M390: Exhibits very slow wear rates due to its high wear resistance but may develop small chips if used improperly on hard materials.
- N690: Wears more evenly than M390 but at a faster rate due to its lower wear resistance[4].
Practical Applications
Both steels are suitable for different types of knives based on their unique properties:
- M390: Ideal for premium folding knives, EDCs (Everyday Carry), tactical blades, and kitchen knives where edge retention and corrosion resistance are paramount.
- N690: Better suited for outdoor knives, hunting blades, or general-purpose tools where toughness and ease of sharpening are more important than extreme edge retention.
Manufacturing Considerations
When comparing M390 and N690, it’s essential to understand the manufacturing processes behind these steels, as they directly impact performance, cost, and availability. Both M390 and N690 are produced by Böhler-Uddeholm, but the methods used to create these steels differ significantly.
Powder Metallurgy vs Conventional Steel Production
- M390: M390 is produced using powder metallurgy (PM) technology. This process involves atomizing molten steel into fine powder, which is then compressed and sintered into a solid form. The result is a steel with a very fine grain structure and uniform distribution of carbides. This uniformity contributes to M390’s excellent wear resistance, edge retention, and corrosion resistance. However, PM steels are more expensive to manufacture due to the complexity of the process and the specialized equipment required.
- N690: N690 is produced using conventional steel production methods. This involves melting the alloying elements together in a furnace, followed by casting the molten steel into ingots. The ingots are then hot-rolled or forged into the desired shape. Conventional production is less costly than powder metallurgy, making N690 more affordable. However, this process results in a coarser grain structure compared to PM steels like M390, which impacts wear resistance and edge retention.
Cost Implications
The difference in manufacturing processes leads to significant cost differences between M390 and N690.
- M390: Due to its powder metallurgy production process and superior performance characteristics, M390 is generally more expensive. It is often found in high-end knives and premium tools where performance is prioritized over cost.
- N690: N690 is more affordable due to its conventional production method. It offers good performance at a lower price point, making it a popular choice for mid-range knives where toughness and ease of sharpening are valued over extreme edge retention.
In summary:
- M390: Higher cost due to powder metallurgy production.
- N690: Lower cost due to conventional production methods.
Heat Treatment Considerations
The heat treatment process is crucial for both M390 and N690 steels because it determines their final hardness, toughness, and overall performance. Each steel has specific heat treatment requirements that must be followed to achieve optimal results.
M390 Heat Treatment
M390’s complex alloy composition requires precise control during heat treatment to maximize its potential.
- Austenitizing: The steel must be heated to around 1180°C (2156°F) to dissolve carbides and form austenite.
- Quenching: After reaching the desired temperature, M390 should be rapidly cooled (quenched) in oil or air. This step locks the microstructure in place.
- Tempering: Tempering is typically done at around 180°C to 200°C (356°F to 392°F) for optimal hardness without sacrificing too much toughness. Multiple tempering cycles may be required for maximum performance.
Due to its high vanadium content and fine grain structure from powder metallurgy, M390 can achieve hardness levels between 60-62 HRC, which gives it excellent wear resistance and edge retention.
However, the complexity of its heat treatment makes it more challenging for manufacturers and custom knife makers alike. Small variations in temperature or quenching speed can lead to suboptimal results such as brittleness or reduced corrosion resistance.
N690 Heat Treatment
N690 has a simpler composition compared to M390, which makes its heat treatment process less demanding:
- Austenitizing: The steel should be heated to approximately 1050°C (1922°F).
- Quenching: Like M390, N690 can be quenched in oil or air.
- Tempering: Tempering is usually done at around 175°C to 225°C (347°F to 437°F) depending on the desired balance between hardness and toughness.
N690 can achieve hardness levels around 58-60 HRC, which provides a good balance between edge retention and toughness. The simpler heat treatment process makes N690 easier to work with for both large-scale manufacturers and custom knife makers.
Real-World Performance
While laboratory tests provide valuable data on properties like hardness and corrosion resistance, real-world performance often reveals additional insights into how these steels behave under practical conditions.
Edge Geometry Impact
The geometry of the knife’s edge plays a significant role in determining how well a blade performs in real-world tasks like cutting, slicing, or chopping.
- M390: Due to its high hardness and wear resistance, M390 excels with thin edges that maintain sharpness over extended periods of use. However, if the edge becomes too thin or acute, it may be prone to chipping under heavy use or impact.
- N690: N690’s higher toughness allows for slightly thicker edges that can withstand more abuse without chipping or rolling. This makes it better suited for knives that will encounter hard materials or rough use, such as outdoor survival knives or hunting blades.
Sharpening Characteristics
One of the most significant differences between M390 and N690 is how easy they are to sharpen:
- M390: While M390 holds an edge for an exceptionally long time, sharpening it can be challenging due to its high vanadium carbide content and hardness (60-62 HRC). Diamond stones or advanced sharpening systems are often required to restore a razor-sharp edge.
- N690: In contrast, N690 is much easier to sharpen using conventional sharpening tools like ceramic rods or whetstones. Its lower hardness (58-60 HRC) means that users can quickly restore an edge without needing specialized equipment.
Wear Patterns
Wear patterns refer to how evenly or unevenly a blade wears down over time with regular use:
- M390: Thanks to its high wear resistance from vanadium carbides and fine grain structure, M390 exhibits slow wear rates even after prolonged use. However, if used on very hard materials like bone or metal, small chips may develop along the edge.
- N690: While N690 wears down faster than M390 due to its lower wear resistance, it tends to wear more evenly without developing chips or cracks under normal use conditions.
Practical Applications & Limitations
Both steels have their strengths and weaknesses depending on the intended application:
- M390:
- Best suited for premium folding knives (EDC), tactical blades, high-end kitchen knives where long-lasting sharpness and corrosion resistance are crucial.
- Not ideal for heavy-duty outdoor tasks involving impact forces (e.g., chopping wood), as it may chip under extreme stress.
- N690:
- Excellent choice for outdoor knives (hunting/survival), general-purpose fixed blades where toughness and ease of sharpening are more important than extreme edge retention.
- Less suitable for applications requiring prolonged cutting performance without resharpening.
Direct Comparison Table
| Property | M390 | N690 |
|---|---|---|
| Edge Retention | 950-1000 TCC | 600-650 TCC |
| Toughness | Moderate | High |
| Corrosion Resistance | Excellent | Very Good |
| Maximum Hardness | 60-62 HRC | 58-60 HRC |
| Sharpening Ease | Difficult | Easy |
| Wear Resistance | Very High | Moderate |
| Cost Factor | High | Moderate |
Conclusion
When deciding between M390 and N690 steels for your next knife purchase or project, it’s essential to consider your specific needs:
- If you prioritize long-lasting sharpness, superior corrosion resistance, and don’t mind paying a premium price for top-tier performance, then M390 is an excellent choice for high-end EDCs or kitchen knives.
- If you need a tough blade that can withstand rough use while being easy to maintain in the field without specialized sharpening tools, then N690 offers great value at a lower cost.
Ultimately, both steels have their place in the world of knife-making—your choice should depend on your intended application and personal preferences.
FAQs
- Which steel holds an edge longer?
- M390 holds an edge significantly longer than N690 due to its higher hardness and wear resistance.
- Which steel is easier to sharpen?
- N690 is easier to sharpen using standard tools like whetstones or ceramic rods compared to M390 which requires diamond stones.
- Is M390 worth the higher price?
- For applications requiring extreme edge retention and corrosion resistance (e.g., premium EDCs), yes—M390’s performance justifies its higher cost.
- Which steel is better for outdoor knives?
- N690 is generally better suited for outdoor knives due to its higher toughness and ease of maintenance in rugged conditions.
Citations:
[1] https://www.shieldon.net/n690-bohler-steel-the-practical-choice-for-your-knives/
[2] https://nobliecustomknives.com/m390-steel/
[3] https://www.knivesandtools.com/en/ct/bohler-m390-steel.htm
[4] https://www.bladeforums.com/threads/bohler-n690-or-m390-for-the-bradford-guardian-3.1462182/
[5] https://nobliecustomknives.com/best-knife-steel/
[6] https://coltellimania.com/acciaio-m390/
[7] https://www.reddit.com/r/chineseknives/comments/1f1wnb0/question_what_is_the_most_affordable_genuine_m390/
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