When it comes to knife steel, two names often come up in discussions among enthusiasts and manufacturers alike: CPM S90V and D2. Both steels are highly regarded for their performance in knives, though they serve different purposes due to their distinct compositions and properties.
Understanding the differences between these two steels requires a deep dive into their chemical makeup, performance metrics, heat treatment requirements, and real-world applications.
This article will provide a scientific comparison of S90V and D2, focusing on measurable properties such as edge retention, toughness, hardness, and corrosion resistance. By the end, you’ll have a clear understanding of which steel might be best suited for your needs.
Composition Analysis
The chemical composition of a steel plays a crucial role in determining its performance characteristics. Below is a comparison of the key elements in S90V and D2:
| Element | CPM S90V (%) | D2 (%) |
|---|---|---|
| Carbon | 2.30 | 1.55 |
| Chromium | 14.00 | 12.00 |
| Molybdenum | 1.00 | 0.80 |
| Vanadium | 9.00 | 0.90 |
| Iron | Balance | Balance |
Key Alloying Elements and Their Impact
- Carbon (C): Carbon increases hardness and wear resistance in both steels but is significantly higher in S90V (2.30%) compared to D2 (1.55%). This higher carbon content contributes to S90V’s superior edge retention.
- Chromium (Cr): Chromium provides corrosion resistance and hardness. S90V contains slightly more chromium (14%) than D2 (12%), which enhances its corrosion resistance, making it more suitable for environments where rust is a concern.
- Vanadium (V): Vanadium is crucial for wear resistance due to the formation of hard vanadium carbides. S90V contains a massive 9% vanadium compared to just 0.9% in D2, giving it exceptional wear resistance but making it harder to sharpen.
- Molybdenum (Mo): Both steels contain molybdenum, which improves toughness and corrosion resistance. However, S90V has a slightly higher concentration (1%) than D2 (0.8%).
Performance Metrics
Edge Retention
Edge retention is often measured using the CATRA test, which simulates cutting performance over time by measuring how long a blade can maintain its sharpness.
- CPM S90V: Due to its high volume of vanadium carbides, S90V exhibits excellent edge retention, scoring around 950 TCC (Total Card Cut) on the CATRA test[3]. This makes it one of the best-performing steels in terms of wear resistance.
- D2: While D2 offers good edge retention due to its high carbon content and chromium carbides, it falls short compared to S90V with scores around 450-500 TCC[3]. This makes it suitable for applications that require moderate wear resistance but not extreme durability.
Toughness
Toughness refers to a steel’s ability to resist chipping or breaking under impact or stress.
- CPM S90V: Toughness is not S90V’s strongest attribute due to its high carbide volume. It has lower toughness compared to other steels like CPM 3V or even D2 but still performs better than some other high-edge-retention steels like S125V[4]. Its toughness rating is around 5-6 ft-lbs on the Charpy V-notch test.
- D2: D2 offers better toughness than S90V but is still considered brittle compared to lower-alloy tool steels like A2 or O1[5]. It typically scores around 10 ft-lbs on the Charpy test[3], making it more resistant to chipping but less wear-resistant.
Corrosion Resistance
Corrosion resistance is critical for knives used in humid or salty environments.
- CPM S90V: With 14% chromium and a fine microstructure from Crucible’s Particle Metallurgy process, S90V offers excellent corrosion resistance, comparable to stainless steels like 440C[1][4]. It scores well in saltwater exposure tests.
- D2: Despite having 12% chromium, D2 is only semi-stainless due to its large carbide structure that limits chromium availability for corrosion protection[5]. It performs moderately well in dry environments but is prone to rusting in humid or salty conditions.
Hardness Range
Hardness is typically measured on the Rockwell C scale (HRC), which indicates how hard the steel can become after heat treatment.
- CPM S90V: Can reach up to 59-61 HRC, depending on heat treatment[4]. This high hardness contributes significantly to its wear resistance but makes it more challenging to sharpen.
- D2: Typically ranges from 55-62 HRC, depending on tempering temperatures[5]. While slightly softer than S90V at similar hardness levels, D2 offers a good balance between hardness and toughness.
Heat Treatment Considerations
Heat treatment plays a critical role in optimizing the performance of both steels.
CPM S90V
S90V requires precise heat treatment due to its high alloy content:
- Austenitizing Temperature: Typically heated between 2100°F – 2150°F (1150°C -1175°C) for hardening[4].
- Quenching: Quenching can be done via salt bath or gas quenching at rates exceeding 150°F/min (80°C/min)[4].
- Tempering: Double tempering at temperatures between 400°F – 750°F (200°C -400°C) is recommended for optimal stress relief and dimensional stability[4]. A cryogenic treatment between tempers can further reduce retained austenite.
D2
D2 steel has simpler heat treatment requirements:
- Austenitizing Temperature: Heated between 1800°F -1875°F (982°C -1024°C) for hardening[5].
- Quenching: Oil quenching or air cooling are common methods used for D2[5].
- Tempering: Tempering at around 450°F (232°C) provides the best combination of toughness and hardness for most applications[5].
Real-World Performance Characteristics
Edge Stability
Edge stability refers to how well an edge resists rolling or chipping under use.
- CPM S90V: Due to its extremely hard vanadium carbides, S90V excels at maintaining edge stability during abrasive tasks like cutting rope or cardboard[8]. However, it can chip under heavy impact due to its lower toughness.
- D2: Offers better edge stability under impact but tends to dull faster during abrasive tasks compared to S90V[3].
Sharpening Behavior
Sharpening difficulty often correlates with carbide volume and hardness.
- CPM S90V: Sharpening can be challenging due to its high vanadium carbide content; diamond stones are often recommended for effective sharpening[8].
- D2: Easier to sharpen than S90V but still requires more effort than simpler carbon steels due to its chromium carbides[7].
Wear Patterns
Wear patterns refer to how evenly or unevenly a blade wears down over time.
- CPM S90V: Wears very slowly thanks to its high wear resistance but can develop micro-chips if exposed to heavy impacts or lateral forces[8].
- D2: Wears faster than S90V but tends not to chip as easily under stress[5].
Practical Applications
Both steels excel in different types of knives:
- CPM S90V: Ideal for high-end folding knives or fixed blades where edge retention is paramount and corrosion resistance is needed.
- D2: Often used in industrial cutting tools, hunting knives, and tactical blades where toughness and ease of sharpening are more important than extreme edge retention.
Manufacturing Considerations
Production Methods
- CPM S90V: Produced through Crucible’s Particle Metallurgy process, which ensures uniform carbide distribution and fine microstructure[4]. This method increases manufacturing costs but results in superior performance.
- D2: Manufactured using conventional steelmaking processes like electric arc furnace melting followed by forging and rolling[5]. This makes it less expensive than CPM steels but with larger carbides that affect performance.
Cost Implications
S90V’s complex manufacturing process makes it significantly more expensive than D2. A knife made from CPM S90V can cost up to twice as much as one made from D2 due to material costs and machining difficulties.
Direct Comparison Table
| Property | CPM-S90V | D2 |
|---|---|---|
| Edge Retention | ~950 TCC | ~450 TCC |
| Toughness | ~5 ft-lbs | ~10 ft-lbs |
| Corrosion Resistance | Excellent | Moderate |
| Maximum Hardness | 59–61 HRC | 55–62 HRC |
| Cost Factor | High | Moderate |
Conclusion
In summary:
- If you need extreme edge retention and corrosion resistance for tasks like slicing or cutting abrasive materials over long periods without frequent sharpening, CPM-S90V is the superior choice.
- On the other hand, if you prioritize toughness and ease of sharpening while still needing decent wear resistance and moderate corrosion protection, D2 will serve you better at a lower cost.
Both steels have their strengths depending on the application—S90V excels in premium knives where performance justifies the cost, while D2 remains popular for durable working knives that need frequent resharpening without breaking the bank.
Citations:
[1] https://www.alphaknifesupply.com/Pictures/Info/Steel/CPMS90-DS.pdf
[2] https://leadrp.net/blog/d2-tool-steel-an-overview-of-its-properties-uses-and-benefits/
[3] https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallurgist-toughness-edge-retention-and-corrosion-resistance/
[4] https://www.crucible.com/PDFs/DataSheets2010/dsS90v1%202010.pdf
[5] https://www.alphaknifesupply.com/Pictures/Info/Steel/D2-DS-Carpenter.pdf
[6] https://knifesteelnerds.com/2021/03/25/cpm-magnacut/
[7] https://knifesteelnerds.com/2020/05/01/testing-the-edge-retention-of-48-knife-steels/
[8] https://knifesteelnerds.com/2020/09/28/s90v-and-s125v-knife-steel-history-properties-and-how-to-heat-treat/
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