S30V is a martensitic stainless steel, while CPM M4 is a high-vanadium, tungsten-containing tool steel both produced by Crucible’s Powder Metallurgy process.
S30V is a stainless steel containing 14% chromium, providing excellent corrosion resistance for knives exposed to moisture and outdoor environments.
On the other hand, CPM M4 is a non-stainless high-speed tool steel without any intentional chromium additions, making it more susceptible to corrosion and staining.
However, CPM M4 compensates for its lack of corrosion resistance with superior overall wear resistance and toughness at higher hardness levels.
While S30V offers a good balance of toughness, wear resistance, and corrosion resistance for stainless knife steel.
CPM M4 excels in applications where maximizing edge toughness and wear resistance are the primary concerns, and corrosion resistance is less critical.
It’s important to note that we are specifically discussing the CPM (Crucible Particle Metallurgy) version of M4 steel, and not the conventionally produced M4 steel.
M4 vs S30V Steel At A Glance
| Property | S30V Steel | CPM M4 Steel |
|---|---|---|
| Type | Martensitic Stainless Steel | High-Speed Tool Steel |
| Hardness Range (HRC) | Aim hardness 58 – 61 | Aim Hardness 59 – 65 |
| Wear Resistance | Excellent (CATRA 145% of 440C) | Excellent (Superior to other HSS) |
| Toughness | Good (10 ft-lbs Charpy) | Very Good (20 ft-lbs Charpy @ 65 HRC) |
| Corrosion Resistance | Very Good (Better than 440C) | Poor (Non-stainless) |
| Edge Retention | Excellent | Excellent |
| Grindability | Good (Powder metallurgy) | Good (Finer than conventional HSS) |
Hardness
S30V and M4 steels exhibit different hardness characteristics that can impact their knife application performance.
The datasheet for CPM M4 steel shows that it can achieve hardness values in the 59-65 HRC range depending on the austenitizing temperature and tempering conditions.
On the other hand, the datasheet for CPM S30V steel indicates a typical hardness range of 58-61 HRC however, it can get up to 64HRC.
In general, higher hardness can lead to better edge retention and wear resistance in knives, but it may also reduce toughness and increase the risk of chipping or breaking underside loads or impacts.
Toughness
M4 high-speed tool steel exhibits better toughness than S30V stainless steel, which could affect their performance in knife applications.
S30V datasheet shows Charpy V-notch impact test results indicating its transverse toughness is around 10 ft-lbs at typical knife hardnesses of 58-61 HRC.
While not bad, this is noted as being only about 4 times better than other comparable stainless steels like 154CM and 440C.
In contrast, the M4 achieves relatively good toughness for high-speed steel. At 65 HRC, it demonstrates a Charpy V-notch impact energy of 20 ft-lbs, double that of S30V at a similar high hardness level.
The toughness curves also show that M4 retains better toughness than S30V as tempering temperatures decrease to achieve higher hardness.
The superior toughness of M4 can be beneficial for knives, especially larger blades, as it increases resistance to chipping and breaking from side impacts or prying loads.
The higher toughness allows M4 knife blades to be hardened to higher levels without becoming excessively brittle.
Edge Retention
Both S30V and M4 steels offer comparable wear resistance and edge retention properties suitable for most knives.
S30V datasheet shows results from CATRA (Cutlery & Allied Trades Research Association) testing, which measures relative wear resistance.
S30V scored 145% better edge retention compared to 440C stainless steel, making it one of the better-performing stainless steels in this test in terms of slicing edge retention.
On the other hand, the M4 datasheet highlights its excellent wear resistance stemming from its high vanadium and carbon content that allows the formation of hard vanadium carbides.
Comparative crossed-cylinder wear testing shows that M4 has wear resistance that is superior to other high-speed steels like M2.
The slightly higher maximum hardness potential of M4 steel (65 HRC) compared to S30V (64 HRC) suggests that M4 may offer better edge retention and wear resistance for knives.
However, the actual performance will depend on other factors such as heat treatment and knife geometry.
Corrosion Resistance
S30V stainless steel has a significant advantage over M4 tool steel in terms of corrosion resistance.
S30V is martensitic stainless steel containing around 14% chromium, which gives it good corrosion resistance properties.
According to the crucible datasheet, S30V corrosion resistance is similar to or better than other high chromium stainless steels like 440C.
The pitting potential measurements in 5% sodium chloride solution show S30V exhibiting better resistance to pitting and crevice corrosion compared to 440C and 154CM stainless steels.
On the other hand, M4 is classified as high-speed tool steel without any intentional additions of chromium or other elements to provide stainless or corrosion-resistant properties.
As a non-stainless grade, M4 would be expected to have relatively poor corrosion resistance, especially in more aggressive environments involving chlorides, acids, etc.
Ease of Sharpening
S30V knife steel and CPM M4 high-speed tool steel can present challenges when it comes to sharpening and grinding due to hard vanadium carbides in their microstructures.
These hard carbide particles increase wear resistance but also make the steels more abrasive and resistant to material removal during sharpening.
However, CPM M4 may be slightly more difficult to sharpen compared to S30V due to its hardness, carbide volume and composition.
CPM M4 can achieve higher maximum hardness levels up to around 65 HRC, whereas S30V typically tops out at 61 HRC. Higher hardness correlates with more difficulty in sharpening and grinding.
While both steels contain vanadium carbides, CPM M4 has a higher total carbide volume (around 20% compared to 14.5% for S30V) with a higher proportion of the ultra-hard vanadium-rich carbides.
CPM M4 steel high tungsten content of 5.5% likely contributes to its grindability resistance compared to S30V which lacks tungsten additions.
Final Thoughts on M4 vs S30V Steel
In my opinion, S30V steel is an excellent all-around stainless steel that is well-suited for a wide variety of knives.
While not the absolute best in any category, S30V performs admirably across the board without major drawbacks.
However, if maximizing toughness and wear resistance is the top priority, I would lean towards CPM M4 for certain heavy-duty or hard-use knife applications.
The data clearly shows M4 exhibiting superior toughness compared to S30V, especially at higher hardness levels.
This increased edge toughness makes M4 more resistant to chipping or breaking under heavy impacts or prying loads that can compromise thinner knife edges.
For knives that will see heavy cutting of thick or abrasive materials, CPM M4 may provide longer-lasting edges compared to S30V.
The trade-off is that as a non-stainless steel, M4 steel lacks proper corrosion resistance.
Proper care through diligent cleaning and drying would be required to prevent staining or rusting, especially in humid environments. This could be a deal-breaker depending on the intended knife use case.
Ultimately, for an all-purpose folding pocket knife or outdoor utility blade where corrosion resistance is important, I would likely choose S30V.
But for a heavy fixed-blade survival or camping knife where ultimate toughness trumps corrosion resistance, CPM M4 could be an excellent choice if I’m willing to maintain the blade meticulously.