Knife enthusiasts hold their metals dear, and for good reason. The steel your blade is crafted from impacts its edge retention, toughness, and ultimately, its ability to perform. Among the contenders, CPM M4 steel has garnered a passionate following. But is CPM M4 steel good for knives? Is this American-made marvel truly deserving of the hype?
In my CPM M4 steel review, I will dissect its composition, dive into its performance characteristics, and unveil the benefits that make M4 a standout choice for many knife makers and users. Buckle up, and get ready to discover if CPM M4 could be the perfect blade buddy for your next cutting adventure!
What is CPM M4 steel?
Hailing from the United States, CPM M4 steel stands out as an exceptionally versatile high-speed steel. Its claim to fame lies in its extremely high carbon and vanadium content, granting it unmatched abrasion resistance. This characteristic makes it the ideal partner for high-quality cutting tools across various domains, particularly when tackling challenging materials like heat-treated components, castings, and abrasive alloys.
Pushing the boundaries, CPM M4 boasts the ability to be hardened beyond 65 HRC, translating to an incredibly sharp and durable edge. However, this exceptional hardness comes at a trade-off. The high vanadium carbide content makes it significantly more challenging to grind post-heat treatment compared to its counterparts like M2.
Despite this hurdle, CPM M4 has captured the hearts of the knife-making community. Its unique properties make it a popular choice for custom knives, where individual customer specifications reign supreme. In conclusion, CPM M4 defines itself as a highly versatile, exceptionally tough, and abrasively resistant steel, carving its niche within the demanding world of high-performance cutting tools and custom knives.
Chemical composition of CPM M4 steel
Imagine a steel cocktail where each ingredient packs a punch. That’s CPM M4! Carbon gives it razor-sharp bite, while chromium stands guard against rust. Molybdenum and vanadium combine to form a formidable team, ensuring the blade stays tough and sharp, cut after cut.
The composition varies somewhat from manufacturer to manufacturer, here is Crucible’s composition based on their data sheet (see here):
| Element | Portion | Effect |
| Chromium | 4.0% | Enhances strength and corrosion resistance, protecting your blade from the elements. It increases tensile strength because it acts as a carbide former. Use of rust-proof or stainless steel, as it increases corrosion resistance from a mass proportion of 12.2%. Reduction in weldability. |
| Carbon | 1.42% | Increasing hardness and tensile strength. In larger quantities, increase in brittleness and reduction in forgeability and weldability. |
| Manganese | 0.3%-(0.7%) | Improves hardness and tensile strength. |
| Molybdenum | 5.25% | Improves hardenability, tensile strength and weldability. Reduction in forgeability and ductility. |
| Sulfur | 0.06%-(0.22%) | Increases machinability but also brittleness. |
| Vanadium | 4.0% | Increasing hardness, increasing wear resistance and improving tempering resistance. |
| Wolfram | 5.5% | Increase in heat strength, tempering resistance and wear resistance at high temperatures up to red heat. |
Is CPM M4 rust-free or a stainless steel?
CPM M4 steel is not rust-free and not considered a stainless steel. Despite containing a small amount of chromium (around 4%), it doesn’t meet the minimum threshold of 12% chromium required to be classified as stainless. As a result, it can develop rust or patina if not properly cared for.
Here’s a breakdown for clarity:
- Stainless steel: Contains at least 12% chromium, offering good corrosion resistance against rust and stains.
- CPM M4: Although higher in chromium content than carbon steel, it falls short of the 12% threshold, making it susceptible to rust or patina.
However, the story doesn’t end there. CPM M4 offers advantages in other areas:
- High hardness and edge retention: Holds a sharper edge for longer than many stainless steels.
- Toughness and wear resistance: Handles demanding tasks without chipping or breaking.
So, while it’s not “rust-free” in the true sense, with proper care and maintenance (e.g., wiping dry after use and occasional oiling), CPM M4 can offer excellent performance for many users.
Hardness of CPM M4 steel
CPM M4 steel can achieve a realistic hardness on the Rockwell C scale of 65 HRC, as shown in various data sheets (see resources section). The high hardness comes from the causally high carbon content of this steel.
With such a high hardness, CPM M4 steel knives typically offer high resistance to deformation, scratches and other surface damage. In other words, high hardness is synonymous with high wear resistance.
Related: S30V steel vs D2 for making knives
CPM M4 steel key properties
Here are the properties of CPM M4 steel:
CPM M4 has garnered a loyal following in the knife world, and for good reason. But what makes this American-made steel tick? Let’s dissect its key properties to see if it lives up to the hype:
- Edge Retention: The star of the show! M4 boasts exceptional hardness (up to 65+ HRC) thanks to its high carbon content. This translates to a razor-sharp edge that stays sharper for longer compared to many other steels. However, achieving this hardness comes at a trade-off: sharpening after heat treatment can be trickier.
- Corrosion Resistance: While not technically “rust-proof,” M4 does contain a decent amount of chromium (4%) compared to carbon steels. This provides moderate corrosion resistance, but it’s still susceptible to rust if not cared for properly. Regular cleaning and occasional oiling are crucial.
- Wear Resistance: Another crown jewel. The high vanadium content in M4 forms hard carbides that excel at resisting wear and tear. This makes it ideal for tackling abrasive materials like wood, cardboard, and even metals.
- Toughness: Don’t underestimate M4’s strength. Despite its high hardness, it also exhibits impressive toughness. This means it can withstand impacts and bending without chipping or breaking, making it a reliable choice for demanding tasks.
- Sharpness: As mentioned earlier, M4 is capable of achieving exceptional sharpness, thanks to its fine grain structure and high hardness. But remember, achieving and maintaining that sharpness requires specialized tools and techniques.
- Machinability: The Achilles’ heel of M4. With the increased sulfur content (0.06%), it offers good machinability, without negative effects on toughness. Its hardness and vanadium content make it significantly harder to machine compared to other steels like M2. This translates to higher manufacturing costs and requires specialized equipment.
The Verdict: CPM M4 isn’t perfect, but it offers a unique blend of properties that make it a favorite for specific applications. If you prioritize edge retention, wear resistance, and toughness in tasks that involve abrasive materials, M4 can be a great choice.
However, be prepared for its demanding sharpening needs and moderate corrosion resistance. Remember, proper care and maintenance are essential to get the most out of this high-performance steel.
Here is a video review of CPM M4 steel for you:
Is CPM M4 a good knife steel?
Of course, it is! It is an excellent choice for those looking for a balance between hardness, toughness, wear resistance and corrosion resistance. As mentioned earlier, the rule is usually “hardness, toughness, corrosion resistance, pick two”. In an almost magical way, CPM M4 combines all three. Corrosion resistance is not on par with the other parameters, BUT still good compared to other steels.
Comparison of CPM M4 with other steels
Comparison of the main properties of CPM M4 and M390, CPM S30V and CPM 3V in tabular form, values on a scale of 1 – 10:
| Criteria | CPM M4 | M390 | CPM S30V | CPM 3V |
| Edge retention | 8/10 | 8/10 | 5/10 | 6/10 |
| Simplicity of sharpening | 3/10 | 5/10 | 5/10 | 5/10 |
| Corrosion resistance | 3/10 | 8/10 | 7/10 | 4/10 |
| Toughness | 6/10 | 6/10 | 6/10 | 10/10 |
M390 and CPM M4 both have the same edge retention and toughness. The difference is that M390 has better corrosion resistance and is slightly easier to sharpen compared to M4.
CPM S30V offers better corrosion resistance and lower edge retention compared to CPM M4, whereas CPM 3V offers better corrosion resistance compared to CPM M4, but with lower edge retention.
Conclusion: Is CPM M4 steel good for knives?
So, the question remains: is CPM M4 steel good for knives? The answer, as always, is “it depends.”
If you prioritize:
- Razor-sharpness that lasts: M4 excels with exceptional edge retention.
- Toughness for demanding tasks: It shines in resisting wear and tear.
- Easy sharpening (for enthusiasts): While not beginner-friendly, it responds well to proper techniques.
However, be aware of:
- Moderate corrosion resistance: Requires more care than stainless steels in humid or wet environments.
- Specialized sharpening needs: Not your average kitchen knife material.
Ultimately, the best steel depends on your specific needs and usage.
For:
- Dry environments: M4 can be a fantastic choice with proper care.
- Demanding tasks: Its toughness and abrasion resistance shine.
- Enthusiasts who enjoy sharpening: With the right tools and skills, M4 rewards you with exceptional performance.
Consider other options if:
- Corrosion is a major concern: Steels like H1 or LC200N offer better protection.
- Ease of maintenance is paramount: Opt for more rust-resistant alternatives.
Remember: Understanding your needs and the trade-offs of each steel is key to finding the perfect blade buddy. If you’re willing to embrace M4’s limitations and provide it with some TLC, it could be your cutting companion for years to come. So, research, weigh your options, and choose the steel that best suits your cutting adventures!
Resources:
- https://www.griggssteel.com/high-speed-steel/pm-m4-steel/
- https://www.carpentertechnology.com/resources
