CPM S90V and M4 are two high-performance steels that have become staples in the knife-making industry due to their exceptional properties. Both steels are known for their specific strengths, but they cater to different needs depending on the application.
CPM S90V is renowned for its extreme wear resistance and corrosion resistance, making it ideal for knives that need to hold an edge for extended periods.
On the other hand, M4 is celebrated for its toughness and ability to withstand impact, making it a popular choice for hard-use tools and knives.
This comparison will focus on scientific data and measurable properties, such as chemical composition, edge retention, toughness, hardness, corrosion resistance, and more. By analyzing these factors in detail, we can determine the best use cases for each steel and provide recommendations based on real-world performance.
Composition Analysis
The chemical composition of a steel alloy significantly affects its performance characteristics. Below is a comparison of the chemical makeup of CPM S90V and M4.
| Element | CPM S90V (%) | M4 (%) |
|---|---|---|
| Carbon (C) | 2.30 | 1.42 |
| Chromium (Cr) | 14.00 | 4.00 |
| Vanadium (V) | 9.00 | 4.00 |
| Molybdenum (Mo) | 1.00 | 5.25 |
| Tungsten (W) | – | 5.50 |
| Cobalt (Co) | – | 0.50 |
Key Alloying Elements and Their Impact
- Carbon (C): Carbon increases hardness and wear resistance in both steels. S90V has a higher carbon content (2.30%) compared to M4 (1.42%), contributing to its superior edge retention.
- Chromium (Cr): Chromium provides corrosion resistance by forming a protective oxide layer on the steel’s surface. S90V has significantly more chromium (14%) than M4 (4%), making it far more resistant to rust.
- Vanadium (V): Vanadium forms hard vanadium carbides that enhance wear resistance. With 9% vanadium content, S90V has an edge over M4 in terms of wear resistance.
- Molybdenum (Mo) & Tungsten (W): These elements improve toughness and high-temperature strength in both steels, with M4 having higher levels of both molybdenum and tungsten, which contribute to its excellent toughness.
Performance Metrics
Edge Retention
Edge retention is one of the most critical factors for knife enthusiasts, as it determines how long a knife can maintain sharpness before needing resharpening. The CATRA test is commonly used to measure edge retention by simulating cutting performance over time.
- CPM S90V: CATRA testing shows that S90V excels in edge retention due to its high vanadium content and hard carbide formation, outperforming many other steels in this regard.
- M4: While M4 also provides good edge retention, especially when compared to simpler carbon steels, it cannot match the extreme wear resistance of S90V.
Toughness
Toughness refers to a steel’s ability to absorb impact without fracturing or chipping. This property is crucial for knives subjected to heavy-duty tasks like chopping or batoning.
- CPM S90V: Despite its excellent wear resistance, S90V sacrifices toughness due to its high carbide volume. It is more prone to chipping under heavy use.
- M4: M4 shines in this category with much higher toughness values than S90V. Its combination of molybdenum and tungsten gives it the ability to withstand significant impact without breaking or chipping.
Corrosion Resistance
Corrosion resistance is essential for knives exposed to moisture or harsh environments.
- CPM S90V: With 14% chromium content, S90V offers superior corrosion resistance compared to most tool steels, including M4.
- M4: M4 has relatively poor corrosion resistance due to its low chromium content (4%). It requires regular maintenance and oiling if used in humid or wet conditions.
Hardness Range
Hardness is measured on the Rockwell C scale (HRC), which indicates how hard the steel is after heat treatment.
- CPM S90V: Typically hardened between HRC 59-62[1], offering a balance between hardness for edge retention and some degree of toughness.
- M4: Can reach hardness levels between HRC 62-65[5], making it harder than S90V but with better toughness at those levels.
Heat Treatment Considerations
Heat treatment plays a vital role in optimizing the performance of both CPM S90V and M4 steels.
CPM S90V Heat Treatment
To achieve optimal properties in CPM S90V:
- Austenitize at temperatures between 2100°F and 2150°F[1].
- Quench using either salt quenching or positive pressure gas quenching.
- Double temper at temperatures ranging from 400°F to 750°F[1]. Freezing treatments can be used between tempers to reduce retained austenite.
S90V requires precise control during heat treatment due to its high vanadium content and complex carbide structure.
M4 Heat Treatment
For M4:
- Austenitize at temperatures around 2050°F[5].
- Quench using oil or air cooling.
- Double temper at around 1000°F[3].
M4’s heat treatment process is less complex than that of S90V but still requires careful handling to achieve maximum toughness without sacrificing hardness.
Real-World Performance
Edge Stability
Edge stability refers to how well a blade maintains its sharpness under stress without deforming or chipping.
- CPM S90V: Due to its high hardness and carbide volume, S90V maintains excellent edge stability during light cutting tasks but may chip under heavy impact.
- M4: Offers better edge stability under impact-heavy tasks due to its superior toughness, making it ideal for chopping or prying applications.
Sharpening Behavior
Sharpening ease varies significantly between these two steels due to their carbide compositions.
- CPM S90V: Sharpening S90V can be challenging because of its high vanadium carbide content, requiring diamond stones or ceramic sharpeners.
- M4: Easier to sharpen than S90V but still requires more effort compared to simpler carbon steels due to its high hardness.
Wear Patterns
Wear patterns develop over time as the blade is used repeatedly.
- CPM S90V: Exhibits minimal wear over time because of its exceptional wear resistance.
- M4: While durable, M4 shows more wear over time compared to S90V but performs better under impact-heavy tasks where toughness is required.
Manufacturing Considerations
Both CPM S90V and M4 are produced using powder metallurgy processes, which result in fine microstructures that improve performance compared to conventionally produced steels.
Production Costs
The cost of manufacturing CPM S90V is generally higher than that of M4 due to:
- Higher alloy content
- More complex heat treatment requirements
- Greater difficulty in machining
M4 is less expensive overall but still considered a premium steel due to its high molybdenum and tungsten content.
Direct Comparison Table
| Property | CPM S90V | M4 |
|---|---|---|
| Edge Retention | Excellent | Good |
| Toughness | Moderate | Excellent |
| Corrosion Resistance | Excellent | Poor |
| Maximum Hardness | HRC 59–62 | HRC 62–65 |
| Cost Factor | High | Moderate |
Conclusion
Both CPM S90V and M4 are exceptional knife steels with distinct strengths:
- Use CPM S90V if you need extreme wear resistance and corrosion protection for light cutting tasks where toughness isn’t critical.
- Choose M4 if you require superior toughness for heavy-duty tasks like chopping or prying but can manage regular maintenance against rust.
In summary:
- For EDC knives where corrosion resistance and edge retention are paramount: go with CPM S90V.
- For hard-use knives where toughness matters most: opt for M4.
FAQs
- Which steel holds an edge longer?
- CPM S90V holds an edge longer due to its high vanadium carbide content.
- Which steel is tougher?
- M4 is significantly tougher than CPM S90V.
- Is CPM S90V stainless?
- Yes, with 14% chromium content, it offers excellent corrosion resistance.
- Which steel is easier to sharpen?
- M4 is easier to sharpen compared to CPM S90V.
- Which steel costs more?
- CPM S90V generally costs more due to its complex composition and manufacturing process.
Citations:
[1] https://www.linkedin.com/pulse/cpm-s90v-steel-heat-treatment-hrc-60-62-cy-tan
[2] https://www.crucible.com/PDFs%5CDataSheets2010%5CdsS35VNrev12010.pdf
[3] https://knifesteelnerds.com/2024/09/17/introduction-to-knife-steel-heat-treating-from-a-metallurgist/
[4] https://www.crucible.com/eselector/prodbyapp/plastics/s90vp.html
[5] https://knifesteelnerds.com/2020/09/28/s90v-and-s125v-knife-steel-history-properties-and-how-to-heat-treat/
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