When it comes to high-performance knife steels, two names frequently come up: CPM S90V and Böhler M390. Both are considered premium materials, known for their exceptional properties like wear resistance, edge retention, and corrosion resistance. However, they differ significantly in terms of chemical composition, toughness, and real-world applications.
This article dives deep into the scientific data behind these two steels, providing a comprehensive comparison based on measurable properties such as chemical composition, edge retention (CATRA test results), toughness, hardness ranges, and corrosion resistance. We’ll also explore their manufacturing processes, heat treatment requirements, and practical performance in everyday use.
By the end of this article, you’ll have a clear understanding of which steel is best suited for your specific needs.
Composition Analysis
The chemical makeup of a steel alloy directly affects its performance characteristics like hardness, toughness, and corrosion resistance. Let’s start by comparing the chemical composition of S90V and M390.
| Element | S90V | M390 |
|---|---|---|
| Carbon (C) | 2.30% | 1.90% |
| Chromium (Cr) | 14.00% | 20.00% |
| Vanadium (V) | 9.00% | 4.00% |
| Molybdenum (Mo) | 1.00% | 1.00% |
| Tungsten (W) | 0.40% | 0.60% |
| Manganese (Mn) | 0.50% | 0.30% |
| Silicon (Si) | 0.50% | 0.70% |
Key Alloying Elements and Their Impact
- Carbon: S90V has a higher carbon content at 2.3%, which contributes to greater hardness and wear resistance compared to M390’s 1.9%.
- Chromium: M390 contains significantly more chromium (20%) than S90V (14%), which enhances its corrosion resistance.
- Vanadium: S90V has more vanadium (9%) than M390 (4%), leading to harder vanadium carbides that improve wear resistance and edge retention.
- Tungsten: Both steels contain tungsten in small amounts to improve hardness and wear resistance.
Performance Metrics
Edge Retention
Edge retention is one of the most critical factors for knife enthusiasts, especially for tasks requiring prolonged sharpness.
- S90V: Known for its exceptional edge retention due to its high vanadium carbide content (~9%). CATRA tests show that S90V performs exceptionally well in edge retention compared to other steels.
- M390: Also offers excellent edge retention but slightly lower than S90V due to its lower vanadium content (~4%). However, its chromium carbides provide good wear resistance.
CATRA Test Results
In CATRA testing, which measures how long a steel can maintain a sharp edge:
| Steel | Relative Edge Retention (CATRA) |
|---|---|
| S90V | ~245 |
| M390 | ~210 |
S90V outperforms M390 in edge retention by about 15-20%, making it ideal for users who prioritize long-lasting sharpness[2][3].
Toughness
Toughness refers to the steel’s ability to resist chipping or breaking under stress.
- S90V: While it excels in wear resistance and hardness, S90V’s toughness is somewhat compromised due to its high carbide volume (~15%). It has moderate toughness compared to other premium steels but is still more brittle than M390.
- M390: Offers better toughness than S90V due to its more balanced carbide structure with fewer vanadium carbides and more chromium carbides (~22%). This makes M390 more resistant to chipping under impact or lateral stress[8].
Charpy Impact Toughness
Measured in ft-lbs:
| Steel | Toughness (ft-lbs) |
|---|---|
| S90V | ~5 |
| M390 | ~7 |
M390 demonstrates superior toughness compared to S90V by about 40%, making it better suited for tasks involving impact or lateral forces[2][8].
Corrosion Resistance
Corrosion resistance is crucial for knives exposed to moisture or harsh environments.
- S90V: With 14% chromium content, S90V qualifies as stainless steel but offers lower corrosion resistance compared to M390.
- M390: Its higher chromium content (20%) gives it superior corrosion resistance, making it ideal for use in wet or marine environments[3][8].
Saltwater Exposure Ratings
On a scale of 1-10:
| Steel | Corrosion Resistance Rating |
|---|---|
| S90V | ~7 |
| M390 | ~9 |
M390 is clearly the better choice for applications where corrosion resistance is paramount[6][8].
Hardness Range
Hardness is measured on the Rockwell C scale (HRC), indicating how resistant the steel is to deformation.
- S90V: Typically hardened between 58-61 HRC, with some heat treatments pushing it up to 62 HRC.
- M390: Can achieve similar hardness levels between 60-62 HRC but can be pushed slightly higher with advanced heat treatments[4][5].
Rockwell Hardness (HRC)
| Steel | Hardness Range (HRC) |
|---|---|
| S90V | ~60-62 |
| M390 | ~60-62 |
Both steels offer comparable hardness, but M390 may be slightly easier to heat treat consistently at higher HRC levels[4][5].
Heat Treatment Considerations
Heat treatment plays a crucial role in optimizing the performance characteristics of both steels.
S90V Heat Treatment
For optimal performance:
- Austenitizing temperature: ~2100°F – 2150°F
- Quenching: Air or gas quench
- Tempering: Double temper at temperatures between 400°F – 750°F
A freezing treatment between tempers can further enhance dimensional stability but may reduce corrosion resistance if tempered above 800°F[4].
M390 Heat Treatment
For optimal performance:
- Austenitizing temperature: ~2100°F – 2150°F
- Quenching: Gas quench or oil quench
- Tempering: Double temper at temperatures between 350°F – 500°F
Cryogenic treatment after quenching can improve hardness by reducing retained austenite[5][8].
Real-World Performance
Edge Stability
Both steels offer excellent edge stability due to their high carbide content:
- S90V: Performs well under heavy use but may be prone to micro-chipping at very thin edges due to its brittleness.
- M390: Offers better overall stability with fewer micro-chips under lateral stress due to its superior toughness[6][8].
Sharpening Behavior
Sharpening difficulty depends on the carbide structure:
- S90V: More challenging to sharpen due to its high vanadium carbide content.
- M390: Easier to sharpen than S90V but still requires diamond or ceramic stones for effective sharpening[6][7].
Wear Patterns
Both steels exhibit excellent wear resistance:
- S90V: Shows minimal wear over time but can develop micro-chips under extreme conditions.
- M390: Exhibits smoother wear patterns due to its finer carbide structure[7][8].
Conclusion
Best Use Cases:
- For users requiring maximum edge retention with moderate toughness—such as precision cutting tools or high-end kitchen knives—S90V is an excellent choice.
- For applications requiring a balance between edge retention, toughness, and corrosion resistance—such as outdoor knives or marine environments—M390 is superior.
In summary:
- Choose S90V if you prioritize edge retention and wear resistance over ease of sharpening and toughness.
- Choose M390 if you need better overall toughness and corrosion resistance with slightly easier sharpening behavior.
FAQ
- Which steel holds an edge longer?
- S90V holds an edge longer due to its higher vanadium carbide content.
- Which steel is easier to sharpen?
- M390 is easier to sharpen compared to S90V because of its finer carbide structure.
- Which steel is better for outdoor use?
- M390 is better suited for outdoor use due to its superior toughness and corrosion resistance.
- Can both steels be used in marine environments?
- Yes, but M390 performs better in corrosive environments because of its higher chromium content.
Citations:
[1] https://blog.hdmdknives.com/s90v-steel.html
[2] https://knifesteelnerds.com/2020/09/28/s90v-and-s125v-knife-steel-history-properties-and-how-to-heat-treat/
[3] https://cdn.prod.website-files.com/65dccaa56e9f327ead622d79/66fb42a7c32c18d3273c487a_pesagolizebo.pdf
[4] https://www.linkedin.com/pulse/cpm-s90v-steel-heat-treatment-hrc-60-62-cy-tan
[5] https://nobliecustomknives.com/m390-steel/
[6] https://knifesteelcomparison.com/maxamet-vs-s90v/
[7] https://nobliecustomknives.com/best-knife-steel/
[8] https://knifesteelnerds.com/2020/06/01/m390-steel-history-and-properties-and-20cv-and-204p/
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