MagnaCut and CPM-4V are two high-performance tool steels popular in knife making with some key differences.
MagnaCut is a newly developed powder metallurgy stainless steel created by Dr Larrin Thomas and produced by Crucible Industries.
CPM-4V steel, is also produced by Crucible but is a non-stainless tool steel used for knife applications focused on higher wear resistance.
CPM 4V steel was developed as an iteration of CPM 3V steel with increased wear resistance. MagnaCut on the other hand is created to exhibit CPM 4V performance but with the added advantage of being a stainless steel.
MagnaCut vs CPM 4V Steel At A Glance
| Property | MagnaCut Steel | CPM 4V Steel |
|---|---|---|
| Hardness | 60-63 HRC | 62-64 HRC |
| Toughness | Higher (38 ft-lbs at 62.5 HRC) | Slightly lower (36 ft-lbs at 62 HRC) |
| Edge Retention | Equal | Equal |
| Corrosion Resistance | Much better | Poor |
| Ease of Sharpening | Better than 4V | Lower than MagnaCut |
| Cost | Higher | Lower |
Hardness
In recommended heat treatments, CPM MagnaCut and CPM 4V have broadly similar Rockwell hardness levels in the 60-63 HRC range.
Crucible data sheets recommend an aim hardness of 60-63 HRC for MagnaCut steel and an aim hardness of 62-64HRC for CPM 4V steel.
This hardness greatly contributes to the wear resistance and edge retention of these two knife steels. Both MagnaCut and 4V are able to achieve this high hardness due to the 8% carbides in their microstructure.
MagnaCut blade steel’s high hardness is contributed by the presence of 6.5% Vanadium Carbide and 1.5% Niobium Carbide while CPM 4V hardness is contributed by 8% Vanadium Carbide.
Toughness
Toughness in a knife steel is its ability to resist shock, breaking, or chipping on impact. MagnaCut steel exhibits slightly higher toughness compared to CPM 4V steel.
According to the Charpy impact test data on the MagnaCut data sheet, MagnaCut at 62.5 HRC has a toughness of 38 ft-lbs while 4V at 62 HRC has a toughness of 36 ft-lbs.
This indicates MagnaCut has nearly 6% higher impact toughness than 4V steel when compared at similar hardness levels.
Additional toughness test data for MagnaCut shows it retains toughness above 30 ft-lbs even when hardened to 64 HRC, whereas 4V is expected to have lower toughness at higher hardness.
For measure the toughness of MagnaCut and 4V is very high almost approaching Nitro-V steel level, this is better than most other stainless steel in the market.
MagnaCut advantage in toughness is due to its fine microstructure with vanadium and niobium carbides compared to only Vanadium carbides in 4V steel.
Niobium element is a grain refiner and powerful carbide former, that improves strength and toughness of MagnaCut steel over 4V steel.
Crucible data indicates MagnaCut has better toughness compared to 4V steel across a range of hardness levels.
MagnaCut’s superior toughness gives it an advantage for knife applications where resistance to chipping, cracking or impact damage is critical.
Edge Retention
MagnaCut and CPM-4V knife steel offer a similar level of edge retention according to standardized lab testing as well as practical cutting experiences.
In CATRA cutting tests, MagnaCut matched the performance of CPM-4V, with both steels scoring around 135% compared to 440C.
This indicates comparable wear resistance between MagnaCut and CPM-4V. In rope-cutting tests, MagnaCut scored slightly higher at 62.5 HRC compared to CPM-4V at 62 HRC.
However, in direct comparisons by knifemakers, the two steels performed very similarly in cutting tasks with no noticeable difference.
The comparable edge retention is expected based on the design goals for MagnaCut by Dr Larrin to match CPM-4V steel performance.
Both steels form similar total volumes of rich carbides which provide good edge retention and wear resistance.
MagnaCut also contains some niobium carbides which further enhance wear resistance. However, the net carbide volume and composition are balanced to achieve parity with CPM-4V steel
Corrosion Resistance
The main difference between MagnaCut steel and CPM-4V steel is that MagnaCut steel is stainless steel while 4V steel is a non-stainless steel.
MagnaCut has better corrosion resistance compared to CPM-4V. In a 72-hour salt spray test, MagnaCut showed no signs of corrosion, even matching or exceeding the performance of steels like 20CV and S35VN.
On the other hand, CPM-4V steel, as a non-stainless steel, exhibited visible rusting and corrosion in wet grinding tests.
The key difference is that MagnaCut was designed as a stainless steel by reducing chromium carbides in the microstructure. This results in more chromium being available in solution to provide corrosion resistance.
In contrast, CPM-4V steel contains only 5% chromium, leaving no chromium in solution.
By eliminating chromium carbides, MagnaCut achieves corrosion resistance comparable to premium stainless grades despite having only 10.7% chromium.
The lack of chromium carbide corrosion attack points leads to MagnaCut’s superior corrosion performance over CPM-4V.
While CPM-4V knives will require care to prevent rusting, MagnaCut knives will withstand humid and even saltwater exposure.
As a matter of fact MagnaCut knife steel demonstrated enough corrosion resistance to be included in Spyderco’s Salt Series knives used by divers, fishermen, and marine enthusiasts.
Ease of Sharpening
MagnaCut has moderately better ease of sharpening compared to CPM-4V owing to its fine, uniform carbide structure.
According to knifemakers who have used both steels, MagnaCut appears to have slightly better sharpenability compared to CPM-4V.
The fine and evenly distributed carbide structure of MagnaCut makes it more responsive on sharpening stones.
Knifemaker Big Chris reported that MagnaCut knives grind easier than CPM-4V knives, with great feedback on stones and easy burr removal.
MagnaCut’s easier sharpening is attributed to the finer carbide size. The addition of niobium carbides creates a more uniform carbide network compared to the larger vanadium carbides present in 4V steel.
Knife maker Devin Thomas was also able to sharpen MagnaCut effectively with standard aluminum oxide stones. The fine carbide size prevents issues with “stubborn burrs” that can occur with some steels.
In contrast, CPM-4V’s edges can be more difficult to deburr and sharpen due to the slightly larger carbide structure.
While both blade steels achieve high sharpness, MagnaCut requires less effort and has better stone feedback.
The more refined microstructure gives MagnaCut a sharpenability advantage over CPM-4V, allowing sharper edges to be produced with greater ease.
Final thoughts on MagnaCut vs CPM 4V
In summary, MagnaCut and CPM-4V are both excellent steels for knives but with some important distinctions.
While they have similar hardness, edge retention, and toughness, MagnaCut clearly excels in corrosion resistance and ease of sharpening compared to CPM-4V.
Its refined microstructure makes MagnaCut markedly more stainless and allows it to sharpen easier than 4V, making it ideal for EDC and pocket knives.
Its refined microstructure with the addition of niobium makes MagnaCut more stainless and allows it to sharpen easier than 4V.
However, CPM-4V maintains an advantage in availability and cost over the newer MagnaCut steel.
For knives where corrosion resistance is critical, like saltwater fishing knives, MagnaCut is the superior choice, but CPM-4V remains a top value option for knives when rust resistance is less important.
In high wear or impact knife applications like bushcraft knives, either steel provides excellent edge retention and high toughness.