When selecting the right steel for knives or cutting tools, two popular choices often come up: N690 and D2. Both are high-performance steels, but they offer different properties that make them suitable for various applications.
N690 is known for its excellent corrosion resistance, edge retention, and ease of sharpening, while D2 is celebrated for its high wear resistance and hardness.
This article delves into a detailed comparison of these steels based on scientific data, including their chemical composition, edge retention, toughness, hardness, and corrosion resistance. We will also explore their manufacturing processes, heat treatment requirements, and real-world performance to help you decide which steel is best for your needs.
Composition Analysis
The chemical composition of steel plays a crucial role in determining its mechanical properties. Here’s a breakdown of the key elements in both N690 and D2:
| Element | N690 | D2 |
|---|---|---|
| Carbon (C) | 1.07% | 1.55% |
| Chromium (Cr) | 17.00-19.00% | 12.00% |
| Molybdenum (Mo) | 1.00-1.50% | 0.85% |
| Vanadium (V) | 0.10-0.30% | 0.80% |
| Manganese (Mn) | 0.30-0.50% | 0.45% |
| Silicon (Si) | 0.30-0.60% | – |
| Phosphorus (P) | Max 0.04% | – |
| Sulfur (S) | Max 0.03% | – |
Key Alloying Elements Explained
- Carbon: Both steels have high carbon content, which contributes to their hardness and wear resistance. However, D2 has a higher carbon percentage (1.55%), making it harder but also more brittle compared to N690.
- Chromium: N690 contains significantly more chromium (17-19%) than D2 (12%), which enhances its corrosion resistance and makes it a true stainless steel, whereas D2 is only semi-stainless.
- Molybdenum & Vanadium: Both elements improve toughness and wear resistance in these steels. N690 has lower vanadium content than D2, which affects its carbide formation and wear resistance.
Direct Comparison Table
| Property | N690 | D2 |
|---|---|---|
| Edge Retention | Good | Excellent |
| Toughness | Moderate | High |
| Corrosion Resistance | Excellent | Moderate |
| Maximum Hardness | ~60 HRC | ~62 HRC |
| Cost Factor | Moderate | Low |
Performance Metrics
Edge Retention
Edge retention refers to how long a blade can hold its sharpness during use before needing to be resharpened.
- N690: Known for good edge retention due to its high chromium content and the presence of molybdenum and vanadium carbides that resist wear.
- D2: Superior edge retention compared to N690 because of its higher carbon content and dense carbide structure formed by vanadium and chromium.
In terms of scientific testing, the CATRA test is commonly used to measure edge retention by simulating cutting performance over time:
- N690 typically scores around 600-700 mm in CATRA tests, offering solid performance in general-use knives.
- D2, with its higher hardness and wear resistance, can achieve scores upwards of 800 mm, making it ideal for heavy-duty cutting tasks.
Toughness
Toughness measures a material’s ability to absorb energy before fracturing—essential for tools that undergo impact or stress.
- N690: Offers moderate toughness due to its balanced alloy composition but is not as tough as some tool steels.
- D2: Known for high toughness among tool steels, though it is slightly less tough than other high-carbon tool steels like A2.
Charpy impact tests are used to quantify toughness:
- N690 scores around 20 J/cm², indicating moderate toughness suitable for most knife applications.
- D2, on the other hand, scores higher at around 25 J/cm², making it better suited for tasks requiring impact resistance.
Corrosion Resistance
Corrosion resistance is crucial when using knives in humid or corrosive environments like kitchens or outdoors.
- N690: With a chromium content of up to 19%, N690 offers excellent corrosion resistance, making it ideal for outdoor use or marine environments.
- D2: While D2 contains around 12% chromium—enough to provide some corrosion resistance—it is still classified as semi-stainless due to the formation of chromium carbides that reduce free chromium available for preventing rust.
Saltwater exposure tests show:
- N690 performs exceptionally well with minimal signs of corrosion after prolonged exposure.
- D2, however, shows visible rusting after similar exposure periods unless properly maintained with oil or protective coatings.
Hardness Range
Hardness is measured on the Rockwell C scale (HRC), which indicates how well the steel resists deformation under pressure.
- N690: Achieves a maximum hardness of around 60 HRC, making it hard enough for most cutting applications while still being relatively easy to sharpen.
- D2: Can reach up to 62 HRC, giving it superior edge retention but making it more challenging to sharpen compared to softer steels like N690.
Heat Treatment Considerations
Heat treatment plays a critical role in maximizing the performance characteristics of both N690 and D2 steels.
N690 Heat Treatment
Optimal heat treatment temperatures for N690 involve:
- Austenitizing at around 1050°C – 1100°C
- Quenching followed by tempering at temperatures between 150°C – 300°C, depending on the desired hardness level.
N690 benefits from precise heat treatment control to avoid excessive brittleness while maintaining good edge retention and corrosion resistance.
D2 Heat Treatment
D2 requires higher temperatures during heat treatment:
- Austenitizing at around 1020°C – 1075°C
- Quenching followed by tempering at temperatures between 150°C – 500°C
Due to its high carbon content, D2 can be prone to cracking if not heat-treated carefully, especially during quenching phases where rapid cooling can induce stress fractures.
Real-World Performance
Edge Stability
Edge stability refers to how well a blade maintains its sharpness without chipping or rolling under stress:
- N690: Offers good edge stability due to its balanced composition but may dull faster than D2 under heavy use.
- D2: Provides excellent edge stability in tasks involving hard materials like wood or bone but may chip if subjected to lateral forces due to its brittleness at higher hardness levels.
Sharpening Behavior
Sharpening ease varies significantly between these two steels:
- N690: Easier to sharpen due to its lower hardness (~60 HRC). It responds well to standard sharpening stones and techniques.
- D2: More challenging to sharpen because of its high hardness (~62 HRC) and dense carbide structure. Special diamond stones or powered sharpening systems may be required for efficient sharpening.
Wear Patterns
Wear patterns refer to how evenly or unevenly a blade wears down over time:
- N690: Wears down relatively evenly due to its fine-grain structure but may lose sharpness quicker than D2 in abrasive environments.
- D2: Exhibits slower wear due to its high carbide content but can develop micro-chipping along the edge if subjected to heavy impact forces.
Manufacturing Considerations
When comparing N690 and D2 steel, it’s important to understand the manufacturing processes involved. Both steels are produced using conventional ingot metallurgy, but they differ in terms of ease of manufacturing, machinability, and cost implications.
Production Method: Conventional vs. Powder Metallurgy
- N690: This steel is produced using conventional ingot metallurgy, which involves melting and casting the steel into ingots before being rolled or forged into the desired shape. N690 is relatively easy to machine and weld due to its balanced composition and good ductility[1][2]. The high chromium content makes it more resistant to corrosion during processing, reducing the need for additional protective measures.
- D2: D2 is also produced using conventional ingot metallurgy, but its high chromium and carbon content make it more challenging to machine compared to N690[4]. D2 tends to work-harden during machining, which requires slower cutting speeds and the use of coolants to prevent overheating[4]. Additionally, D2 can be produced using powder metallurgy (CPM-D2), which results in a finer carbide structure that improves toughness and machinability[5].
Machinability
- N690: N690 is known for being relatively easy to machine compared to other high-performance steels[3]. Its good ductility allows for easier shaping and grinding during the knife-making process. However, its high hardness still requires the use of abrasive materials for precise grinding and finishing.
- D2: D2 has a lower machinability rating (around 27%) due to its high wear resistance and tendency to work-harden during machining[4]. This makes it more difficult to machine than N690, requiring specialized tools and techniques. Slow cutting speeds and the use of oil or coolant are necessary to prevent excessive wear on cutting tools.
Cost Implications
- N690: N690 is moderately priced for a high-performance stainless steel, with costs ranging between $10 to $15 per pound[2]. This makes it accessible for both small-scale knife makers and larger manufacturers. Its combination of performance characteristics—good edge retention, corrosion resistance, and toughness—offers excellent value for money.
- D2: D2 is generally less expensive than N690, especially in its conventionally produced form. It is widely available due to its long history of use in industrial tooling applications. However, CPM-D2 (produced via powder metallurgy) can be significantly more expensive due to the specialized production process that enhances its toughness and wear resistance[5].
Heat Treatment Considerations
Heat treatment is a critical factor in maximizing the performance of both N690 and D2 steels. Proper heat treatment can significantly affect hardness, toughness, and wear resistance.
N690 Heat Treatment
- Austenitizing Temperature: N690 requires heating to around 1050°C – 1100°C (1922°F – 2012°F) during the austenitizing phase[3]. This temperature range ensures that the steel reaches its full potential in terms of hardness and edge retention.
- Quenching: After austenitizing, N690 is typically quenched in oil or air to lock in its desirable properties. The quenching process must be carefully controlled to avoid warping or cracking.
- Tempering: Tempering is crucial for reducing brittleness while maintaining hardness. For N690, tempering temperatures range from 150°C – 300°C (302°F – 572°F) depending on the desired hardness level[3]. Lower tempering temperatures result in higher hardness but reduced toughness.
D2 Heat Treatment
- Austenitizing Temperature: D2 requires slightly lower austenitizing temperatures compared to N690, typically around 1020°C – 1075°C (1868°F – 1967°F)[4]. This temperature range allows for optimal carbide formation, which contributes to D2’s excellent wear resistance.
- Quenching: Like N690, D2 benefits from air or oil quenching. However, due to its higher carbon content, D2 is more prone to cracking if not quenched carefully. Air quenching is often preferred as it reduces the risk of warping.
- Tempering: D2 requires tempering at higher temperatures than N690—typically between 150°C – 500°C (302°F – 932°F) depending on the desired balance between hardness and toughness[4]. Higher tempering temperatures reduce brittleness but also lower hardness slightly.
Real-World Performance
Edge Stability
Edge stability refers to how well a blade maintains its sharpness without chipping or rolling under stress.
- N690: Thanks to its balanced composition of chromium, molybdenum, and vanadium carbides, N690 offers good edge stability for most cutting tasks[1][3]. It performs well in general-use knives where moderate impact resistance and corrosion resistance are required.
- D2: D2 provides excellent edge stability due to its high carbon content and dense carbide structure[4][5]. It excels in heavy-duty applications such as cutting hard materials like wood or bone. However, at higher hardness levels (~62 HRC), it may be more prone to chipping if subjected to lateral forces.
Sharpening Behavior
Sharpening ease varies significantly between these two steels:
- N690: Easier to sharpen due to its lower maximum hardness (~60 HRC)[1][3]. It responds well to standard sharpening stones and techniques. Knife enthusiasts often appreciate how quickly they can restore a sharp edge on an N690 blade.
- D2: More challenging to sharpen because of its higher hardness (~62 HRC) and dense carbide structure[4][5]. Special diamond stones or powered sharpening systems may be required for efficient sharpening. However, once sharpened, D2 holds an edge for an extended period.
Wear Patterns
Wear patterns refer to how evenly or unevenly a blade wears down over time:
- N690: Wears down relatively evenly due to its fine-grain structure but may lose sharpness quicker than D2 in abrasive environments like cutting cardboard or rope[1][3].
- D2: Exhibits slower wear thanks to its high carbide content but can develop micro-chipping along the edge if subjected to heavy impact forces[4][5].
Practical Applications
Both steels are used in a variety of knife-making applications:
- N690: Ideal for outdoor knives, kitchen knives, and general-purpose blades where corrosion resistance is critical. Its ease of sharpening makes it popular among users who need a reliable blade that can be quickly maintained in the field.
- D2: Best suited for heavy-duty knives such as hunting knives, tactical blades, or industrial cutting tools where wear resistance and edge retention are paramount. While harder to sharpen than N690, D2’s superior wear resistance makes it ideal for tasks that involve prolonged use without frequent resharpening.
Practical Applications and Use-Case Recommendations
Now that we’ve thoroughly examined the chemical composition, performance metrics, heat treatment requirements, and real-world behavior of N690 and D2, it’s time to explore their practical applications. Each steel has strengths that make it ideal for certain tasks. Whether you’re a knife enthusiast, a professional chef, or someone who needs a durable tool for outdoor adventures, understanding the best use cases for each steel can help you make an informed decision.
Best Use Cases for N690
N690 is a versatile stainless steel with a balanced mix of properties that make it suitable for a wide range of applications. Here are some of the most common uses:
1. Outdoor and Survival Knives
N690’s excellent corrosion resistance makes it ideal for outdoor knives that will be exposed to moisture, humidity, or even saltwater environments. Its moderate toughness ensures it can handle general cutting tasks like preparing food, cutting rope, or carving wood. Additionally, its ease of sharpening in the field is a significant advantage for survivalists who may not have access to specialized sharpening tools.
- Why N690?: The combination of corrosion resistance and ease of maintenance makes N690 a great choice for knives that will be used in harsh environments. It’s also less prone to rusting compared to D2, which is important in outdoor settings.
2. Kitchen Knives
In the kitchen, knives are frequently exposed to water and acidic foods, which can cause rust or corrosion in lower-grade steels. N690’s high chromium content (17-19%) provides excellent protection against rust while maintaining good edge retention. Its moderate hardness (~60 HRC) strikes a balance between durability and ease of sharpening, making it well-suited for professional chefs and home cooks alike.
- Why N690?: For kitchen knives, corrosion resistance is paramount. N690’s stainless properties ensure that your blade remains rust-free even with constant exposure to moisture. Additionally, its ease of sharpening means you can quickly restore a razor-sharp edge when needed.
3. Everyday Carry (EDC) Knives
For everyday carry (EDC) knives, users typically want a blade that is easy to maintain and reliable in various cutting tasks. N690 offers good edge retention without being overly difficult to sharpen. Its toughness is sufficient for light-duty tasks like opening packages or cutting cordage.
- Why N690?: The ease of sharpening and corrosion resistance make N690 an excellent choice for EDC knives that need to be ready for various tasks without requiring frequent maintenance.
Best Use Cases for D2
D2, with its higher hardness and superior wear resistance, excels in heavy-duty applications where edge retention is critical. However, its semi-stainless nature means it requires more care to prevent rusting compared to stainless steels like N690.
1. Hunting and Skinning Knives
D2’s excellent edge retention makes it perfect for hunting knives that need to maintain sharpness through repeated use in tough conditions—such as skinning game or cutting through bone. Its high hardness (~62 HRC) ensures the blade stays sharp even after extended use without frequent resharpening.
- Why D2?: The high wear resistance of D2 allows it to hold an edge longer than N690 during demanding tasks like skinning animals or processing meat. However, hunters will need to take extra care to keep the blade clean and dry after use to prevent rust.
2. Tactical and Combat Knives
For tactical knives used in self-defense or military applications, toughness and edge retention are crucial. D2’s high hardness provides superior cutting power in combat situations where the blade may be subjected to hard impacts or abrasive materials like fabric or leather.
- Why D2?: D2’s wear resistance ensures that tactical blades remain sharp during extended use in the field. However, users should be aware that D2 can chip if subjected to lateral forces due to its brittleness at higher hardness levels.
3. Industrial Cutting Tools
D2 has long been used in industrial applications such as die-cutting tools and shears due to its exceptional wear resistance and ability to hold an edge under heavy use. In these applications, blades made from D2 can cut through tough materials like wood, metal, or plastic without dulling quickly.
- Why D2?: The superior wear resistance of D2 makes it ideal for industrial tools that require long-lasting sharpness under heavy loads. However, its semi-stainless nature means it requires regular maintenance to prevent corrosion in humid environments.
Sharpening Considerations
Sharpening behavior is an important factor when choosing between N690 and D2 steels:
- N690: As mentioned earlier, N690 is easier to sharpen due to its lower maximum hardness (~60 HRC). This makes it suitable for users who prefer low-maintenance blades that can be quickly resharpened using standard sharpening stones.
- D2: On the other hand, D2’s high hardness (~62 HRC) makes it more challenging to sharpen using conventional methods. Diamond stones or powered sharpeners are recommended for maintaining a sharp edge on D2 blades. While harder to sharpen initially, D2 holds an edge much longer than N690 once properly sharpened.
Wear Patterns
Wear patterns differ significantly between these two steels:
- N690: Wears down relatively evenly over time due to its fine-grain structure but may lose sharpness quicker than D2 when subjected to abrasive materials.
- D2: Exhibits slower wear thanks to its high carbide content but can develop micro-chipping along the edge if subjected to heavy impact forces or lateral stress.
Cost vs Performance
When considering cost versus performance:
- N690: Offers excellent value for money given its balanced properties—good corrosion resistance, decent toughness, and ease of sharpening—at a moderate price point.
- D2: While generally less expensive than N690 (in its conventional form), D2 offers superior wear resistance and edge retention at the cost of increased difficulty in sharpening and higher maintenance requirements due to its semi-stainless nature.
Conclusion
In conclusion, both N690 and D2 are excellent knife steels with distinct advantages depending on their intended use:
- If you need a knife with excellent corrosion resistance, moderate toughness, and ease of sharpening—ideal for outdoor activities or kitchen use—then N690 is your best bet.
- If you prioritize edge retention, wear resistance, and are willing to invest more time into maintenance—especially if you’re using the knife for heavy-duty tasks like hunting or industrial work—then D2 will serve you well.
Final Recommendations
| Application | Recommended Steel |
|---|---|
| Outdoor/Survival Knives | N690 |
| Kitchen Knives | N690 |
| EDC Knives | N690 |
| Hunting/Skinning Knives | D2 |
| Tactical/Combat Knives | D2 |
| Industrial Tools | D2 |
Ultimately, choosing between these two steels depends on your specific needs:
- For users who value low maintenance and versatility across various environments (especially where moisture is present), N690 offers an attractive balance between performance and ease of care.
- For those who need maximum durability under heavy use—and are willing to put extra effort into sharpening and maintenance—D2 provides superior wear resistance at a lower cost than many other high-end tool steels.
FAQ
- Which steel holds an edge better—N690 or D2?
- D2 holds an edge better due to its higher hardness (~62 HRC) and dense carbide structure.
- Is N690 easier to sharpen than D2?
- Yes, N690 is easier to sharpen because it has lower hardness (~60 HRC) compared to D2.
- Which steel is more corrosion-resistant?
- N690 is significantly more corrosion-resistant due to its higher chromium content (17-19%), making it stainless steel.
- What are the best uses for D2 steel?
- D2 excels in heavy-duty applications such as hunting knives, tactical blades, and industrial cutting tools where wear resistance is crucial.
- Does N690 require special care?
- While N690 is highly resistant to corrosion, regular cleaning and drying after use will help maintain optimal performance over time.
Citations:
[1] https://oristarmetal.com/en/shop/tool-steel-plate-bohler-n690-austria-66932
[2] https://tsprof.us/blogs/news/n690-the-modern-standard-of-a-knife-steel
[3] https://www.tuofa-cncmachining.com/tuofa-blog/d2-steel.html
[4] https://damascussteelbillets.com/n690-steel-vs-s35vn/
[5] https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallurgist-toughness-edge-retention-and-corrosion-resistance/
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