M4 vs CruWear Steel

CPM CruWear and CPM M4 are premium CPM knife steels manufactured by Crucible Industries through their CPM (Crucible Particle Metallurgy) process.

CPM CruWear is a powder metallurgy cold work tool steel designed as an upgrade to conventional D2 tool steel. 

In contrast, CPM M4 is a high-speed powder metallurgy tool steel with a very high 4% vanadium content.

CPM M4 steel derives its outstanding wear resistance from its high volume of extremely hard vanadium carbides. 

M4 vs CruWear Steel At A Glance

Hardness

CruWear, being an air-hardening cold work tool steel, can achieve higher hardness levels up to around 64-65 HRC through secondary hardening from tungsten and molybdenum additions.

In contrast, CPM M4, a high-speed steel, typically tops out at around 63-64 HRC, relying more on its high vanadium carbide volume for wear resistance than ultra-high hardness. 

For knives, the higher attainable hardness of CruWear can translate to better edge-holding ability and abrasion resistance compared to M4 at equal hardness levels. 

Toughness

Toughness, the ability to absorb impact without fracturing, is an important property for knives to prevent chipping or breakage under heavy use.

CPM CruWear tool steel has a distinct advantage in toughness over CPM M4 tool steel. 

In a Charpy C notch impact test at around 60 HRC, CruWear achieved impact toughness of  80 Joules, while CPM M4 achieved around 45 Joules at 62 HRC. 

This higher toughness allows CruWear knives to withstand heavy chopping better, prying, and impact forces without catastrophically fracturing the edge or blade. 

The increased toughness stems from CruWear’s fine, uniform distribution of carbides made possible by the powder metallurgy process.

In contrast, M4 tends to have larger, more segregated carbide regions that act as stress concentration points, reducing overall toughness.

While M4 may have a slight edge in wear resistance, the superior toughness of CruWear makes it more forgiving and robust for demanding knife applications where impact loads are encountered. 

Edge Retention

CPM CruWear and CPM M4 offer exceptional wear resistance for knives, CPM M4 has a slight advantage over CPM CruWear in overall edge retention ability thanks to its higher 4% vanadium content.

The increased volume of the incredibly hard vanadium carbides in CPM M4 allows it to resist abrasive wear on the cutting edge better. 

However, CruWear’s higher toughness allows it to take and maintain a very thin, acute, cutting-edge geometry without experiencing premature edge rolling or chipping.

So, in the initial stages of use, a CruWear knife can achieve superior sharpness with minimal edge destruction.

But as the edge wears, CPM M4 greater proportion of vanadium carbides allows it to retain a sharper edge for longer before requiring re-sharpening. 

While CruWear’s ultra-high 64-65 HRC hardness is impressive, its M4 hard vanadium carbide composition ultimately provides marginally better long-term edge-holding ability on knives.

Corrosion Resistance

Neither CruWear nor M4 are considered stainless steels, so they do not possess the high corrosion resistance typical of stainless grades with high chromium and molybdenum contents.

However, CruWear exhibits moderately better corrosion resistance between the two due to its higher chromium content of around 7.5% compared to only 4% in M4.

The chromium forms a protective passive oxide layer that imparts some degree of stain and corrosion resistance.

Tempering in the higher temperature range can degrade corrosion resistance in both steels by causing chromium carbide precipitation.

CruWear still maintains an advantage when tempered at lower temperatures around low temperature range which is a more common range for knives.

CruWear properties give it a distinct edge over M4 in maintaining better stain and corrosion resistance for applications where the knife may be exposed to mild corrosive or require periodic etching and cleaning. 

However, neither material should be considered truly corrosion-resistant like stainless steels for harsh environments.

Ease of Sharpening

Cru-Wear and M4 present some challenges as high alloy tool steels, but CruWear has a slight advantage in grindability and ease of sharpening over M4. 

In the annealed condition, their machinability is relatively similar, with CruWear being described as comparable to D2 tool steel. 

The finer carbides in CruWear allow grinding wheels to cut more efficiently with reduced loading and clogging. 

Manufacturers recommend using aluminum oxide or CBN abrasive wheels for best results on these air-hardening tool steels. 

CPM M4 higher vanadium content can make it somewhat more labor-intensive to sharpen, especially for acute cutting edges on knives. 

Cost

Both CPM CruWear and CPM M4 steels are very similar in terms of the cost of grinding and producing them.

However, CPM Cruwear is slightly easier to machine, making it a little cheaper. The price of knives made from these two steels are similar though.

Final Thoughts on M4 vs Cruwear Steel

For everyday carry or outdoor/hard-use knife that may face environmental exposure, I recommend  CPM CruWear knife steel.

Its moderately better corrosion resistance, similar to D2 tool steel, makes it more suitable for harsh environments. 

Additionally, CruWear’s combination of high attainable hardness and good toughness allows it to take and maintain a crazy sharp, fine edge that is easy to re-touch on a strop.

The slightly higher ease of sharpening of CPM CruWear is also a nice advantage for frequent touch-ups.

While CPM M4 may ultimately hold a more degraded edge for longer, CruWear’s ability to get hair popping sharp seems ideal for an EDC blade.

So in summary, for an easy to resharpen EDC-oriented knife, I would probably choose the incredible edge quality and good corrosion resistance of CPM CruWear. 

But for heavy choppers or ultra-tough survival knives, the better wear resistance of CPM M4 could make it the preferred option.