CruWear vs D2

[Cliff Stamp]

There have been many posts here on CruWear and it is an interesting steel having been used a long time under many different names all the way back to VascoWear. In some ways it is easy to find data on it such as this :



But the problem is that such marketing information rarely tells you what they are measuring exactly, how the steels were hardened and what kind of precision they had so interpreting the results is problematic. If you do get some more data often you find that they are doing something like comparing adhesive wear resistance which can show very large differences in HSS vs Cr based steels but there is little correlation between that and abrasive wear which tends to happen in knife use.

The steel itself is an interesting blend of elements as it is a high carbon/tungsten modification to 3V (not that 3V came first, just looking at the difference) which an addition of Silicon. Silicon in small elements is in all steels (it is a deoxidizer) but in large amounts it is added for toughness (it is in the shock steels for example) because among other things it retard the formation of cementite at grain boundaries which happens in tempering (the carbon comes out of the martensite, forms epsilon carbide and then that dissolves and forms cementite). These cementite formations allow brittle failure hence suppressing them allows the tempering of the steel (makes it tougher) without causing the embrittlement of the cementite formation. Due to the higher carbon and tungsten it would be expected to have better abrasive wear than 3V and better hardness, and since this is mainly MC type carbides (small) and the silicon addition, it would be expected to have similar toughness.

But that still leaves the question as to how does it compare to a normal/workhorse steel like D2?

Well I have been looking for that for awhile, the problem is the massive amount of different tradenames doesn't make it easy, but you can save searches now and have results notified which is a help. Here is one such study :

"MACHINING SCIENCE AND TECHNOLOGY Vol. 8, No. 2, pp. 193–210, 2004, Kinematics and Wear of Tool, Blades for Scrap Tire Shredding"

It is an interesting work as it compares 4340 and D2 for such work and then CruWear to D2 extensively. It also mentions 3V and HSS and sort of implies possible future experiments. It also looks at chipping and chipping + wear. Interestingly enough there is no significant difference in chipping, but Cruwear is about 2:1 in terms of an improvement to resist wear. However there is not a lot of detail on how the steels were hardened, and it looks like both had significant retained austenite as the D2 blade was 56 HRC unworn and 59 HRC worn, compared to 58 and 61 for the CruWear. The results might not be as different with varying heat treatments of D2 which can achieve 62 HRC with full martensite.

It is an interesting steel and I am likely to pick up a Spyderco in it at some point. I have 3V, but the problem is that it is normally used in larger blades where I don't like how it performs at all as the grindability is far too low. I would be really interested if anyone has a CruWear from Spyderco and has a decent D2 blade (Dozier for example) and can see a significant difference in wear resistance, or other properties.

[KevinOubre]

CLiff, what exactly does cementite do in the matrix to lessen toughness?

[elena86]

My Manix 2 in Cruwear just arrived so I have no experience with this steel yet.I am as curious as you are.But a friend of mine who has a lot of experience with both D2 and Cruwear is a Cruwear fan.He says is a "more balanced" steel in both toughness and hardness and a better allarounder.But interested enough he prefers D2 in the field.Never told me why and never asked.Maybe you could guess....

[Cliff Stamp]

But a friend of mine who has a lot of experience with both D2 and Cruwear is a Cruwear fan.He says is a "more balanced" steel in both toughness and hardness and a better allarounder.

Whose D2 has he used which he found lacked in performance due to toughness?

[Cliff Stamp]

CLiff, what exactly does cementite do in the matrix to lessen toughness?

Imagine a piece of wood and think about the grain. In general it is easy to split wood along the grain as you can pop the grains of wood apart from each other vs tearing them apart which is what you have to do if you cut cross grain. This is easy to understand and you can do the experiment visually as wood grains are so large you can see them with the naked eye.

Now further imagine that there was a thin layer of ice sandwiched right between the grains in the boundary area. Would that really crappy ice-cream sandwich split easier or harder than regular wood? It should be obvious it would be easier because ice is really brittle compared to wood and it doesn't bond well to wood so the ice could break itself or it could separate from the wood.

Cementite is the same compared to the martensite (the bulk of the steel is martensite, it is what you see when you look at the knife). It is really brittle (as are all carbides) and the interface between cementite and the martensite is another point of fracture (as with all carbides). What is worse is that during tempering from between 200 and 350C it will tend to form on the grain boundries which are already weak points for the same reason they are in wood.

Hence why in general that tempering range should be avoided unless there is something in the steel which retards the formation. That reaction is so strong it even has a name, TME, or blue brittlness. The latter refers to it being the temperature which makes steel turn blue in tempering. Ironically a very common tempering temperature for knives as it tends to produce the magical 60 HRC in a lot of steels.

[KevinOubre]

So is that cementite formation the reason that, in general, the harder you heat treat a steel, the less toughness it has as opposed to a softer state? Does cementite contribute to edge retention at all or is it a wholly undesirable formation in the steel?

[elena86]

But a friend of mine who has a lot of experience with both D2 and Cruwear is a Cruwear fan.He says is a "more balanced" steel in both toughness and hardness and a better allarounder.

Whose D2 has he used which he found lacked in performance due to toughness?

He hand-makes his own fixed blade D2 knives.AFAIK he is a very skilled blacksmith and he learned his skills somewhere in Finland from some Sami people.When he goes buscrafting he uses a D2 neck-knife with a 8 cm wharncliffe blade made by himself.He once told me that the neck-knife I mentioned was hardened between 60-61 HRC.After he purchased the Spyderco Manix 2 in CPM-CRUWEAR and used it for one week in the woods, he was excited.He declared that this folder became his holy-grail and he talked me into buying one too.He owns many Spydercos but he stated that the Manix2 in Cruwear is the best Spyderco ever.

[Cliff Stamp]

He hand-makes his own fixed blade D2 knives.

That is interesting, I would be curious how he is hardening it.

[elena86]

He hand-makes his own fixed blade D2 knives.

That is interesting, I would be curious how he is hardening it.

AFAIK he soak through at 1700-1800°F and reheat as often as necessary.After forging he cool slowly in dry ashes.He told me he is very carefull to decarburization.

[Cliff Stamp]

So is that cementite formation the reason that, in general, the harder you heat treat a steel, the less toughness it has as opposed to a softer state?

Not really, the hardness in steel is mainly due to the carbon dissolved in the martensite. It reaches a maximum at about 0.6% and only goes up slightly above that to 67/68 HRC even if you go way up to 1.5% carbon steels.



The toughness of the martensite is directly dependent on the carbon content, the higher the carbon content the lower the toughness. The carbide volume has only a minor influence, note even in crazy high carbide steels like 121REX they are only 1-2 HRC points harder than 1095.

There are a few reasons why hardness reduces toughness but they are indirect in that the thing causing the hardness also is influencing the toughness, it isn't a direct relationship between hardness and toughness per say, just that both are being controlled by something else, just in opposite ways.

One of the major things is that martensite forms in two main ways, plate and lathe, which just refers to the sub-structure it can have (like a knife can have a hollow or flat grind). The plate form starts happening at high carbon concentrations and it is really brittle. This is why all the really tough steels are mid-carbon steels.

There is more to toughness than carbon content of course, silicon and nickel for example both increase toughness, nickel is extremely dramatic :



Look at the difference between L6, a nickel steel and the same carbon in a plain carbon steel. The nickel is much tougher at a higher hardness. Nickel does a number of things to improve hardness (it creates finer sub-structures, and significantly increases cleavage fracture toughness). It also improves corrosion resistance which is why you see it in stainless steels.

Does cementite contribute to edge retention at all or is it a wholly undesirable formation in the steel?

Cementite is a form of carbide which means it will increase wear resistance. Will it increase edge retention, well that depends on how the edge is blunting. If the edge is blunting from :

-slow wear
-deformation/rolling

Then moving from a 1060 type steel to a 1095 to a 1.5% carbon steel will increase the edge retention. However if the edge is blunting by fracture / micro-chipping then you walk the reverse path from 1.5% carbon down until the chipping stops.

If you have not used a nice ultra-high carbon steel blade you should try one as they are very different in properties than something like VG-10 / ATS-34, they rust extremely fast though but there is a reason wood workers tend to universally praise white steel chisel blades.

[Cliff Stamp]

AFAIK he soak through at 1700-1800°F and reheat as often as necessary.

That is likely the problem. D2 is a very high alloy steel, in order to harden it optimally you have to do something similar to :

-1-2 equalizes in the ramp to the soak temperature
-1000-1050C soak, and this is soak, you have to hold it at that temperature
-oil quench
-extended quench (cryogenics)
-temper as required

The extended quench can be omitted if the tempering is done hot, in which case do multiple high tempers.

D2 is one of the least friendly steels to harden due to the very high alloy content.

[elena86]

AFAIK he soak through at 1700-1800°F and reheat as often as necessary.

That is likely the problem. D2 is a very high alloy steel, in order to harden it optimally you have to do something similar to :

-1-2 equalizes in the ramp to the soak temperature
-1000-1050C soak, and this is soak, you have to hold it at that temperature
-oil quench
-extended quench (cryogenics)
-temper as required

The extended quench can be omitted if the tempering is done hot, in which case do multiple high tempers.

D2 is one of the least friendly steels to harden due to the very high alloy content.

Be sure I will ask him to read this.But, anyways, how would you compare the two steels in real world ?

[KevinOubre]

How does cementite compare to vanadium carbides? I have read and heard of some pretty dramatic, for a plain carbon steel, abrasive wear resistance claims of steels like White #1. I would assume this can come form the cementite? I know Murray Carter loves White #1 and uses it exclusively now. I have actually been looking at some stuff with White steel over at japanwoodworker. Some seem pretty affordable.

[Cliff Stamp]

Be sure I will ask him to read this.But, anyways, how would you compare the two steels in real world ?

I have used a lot of 3V and D2, but have done very little work with the Cru/Vasco/Z-wear steels. 3V, I generally prefer over D2 as it has similar wear resistance, similar hardness, but is much tougher.

[Cliff Stamp]

How does cementite compare to vanadium carbides?

It is much softer, this is why vanadium carbide and tungsten carbide (similar) are used in the cold work tool steels which were traditionally used as cutting tools. They were eventually replaced by the HSS simply due to the ability to cut after very high speeds and not lose hardness due to the heat generated drawing the temper out of the steel.

I have read and heard of some pretty dramatic, for a plain carbon steel, abrasive wear resistance claims of steels like White #1. I would assume this can come form the cementite?

A combination of the cementite and very high hardness.

I know Murray Carter loves White #1 and uses it exclusively now. I have actually been looking at some stuff with White steel over at japanwoodworker. Some seem pretty affordable.

Note that 1095 is a very similar steel, the problem is that in the US it is generally used in cheap knives but if you get a decent knifemaker who knows how to harden it for maximum strength and wear resistance you will get a very fine cutting blade.

Carter tends to argue for White over Blue steels, however I think that is a hard argument to make for most users. But at this point we are talking about very fine distinctions in very similar steels.

[elena86]

Be sure I will ask him to read this.But, anyways, how would you compare the two steels in real world ?

I have used a lot of 3V and D2, but have done very little work with the Cru/Vasco/Z-wear steels. 3V, I generally prefer over D2 as it has similar wear resistance, similar hardness, but is much tougher.

I only wish Spyderco release more knives in D2 steel.I have a bushcraft fixed blade in D2 , it's my go to knife when I go camping and I am very pleased with it.Holds an edge like crazy, no chipping and quite easy to sharpen.I have to kick myself for not buying the Para1 in D2.

[opusxpn]

I got a queen cutlery folder in D2, manix and mili in cruwear, for some reason the D2 was a ***** to get it hair popping sharp compared to the cruwear. Both with a 40 micro even the psf27 mule was easier to get it sharp, why would that be? I mean aren't the 3 very similar?

[The Mastiff]

Cliff, I have several Cruwear/Vascowear blades and probably more D2 blades but they are so different in size and purpose and even hardness that only the most generalized comments could be made which wouldn't be much help here.

I will offer to lend you a Cruwear Mule (ingot version AFAIK) if you ever want it for testing. The one I'd send would have a generic Ti Halperin grip. Just let me know if you ever want to test it . You can likely get some of the heat treat details from Sal if needed. Best I can recall it should be somewhere around rc 62. I'd send you one that hasn't had anything done to it other than renn wax it for storage so you can set the bevels to your preferences. There would be no hurry on it and you can do whatever is needed to it.

You probably know I am a fan of steels in this class I'll say from 3V up to 4V and CPM M4 HC with Cruwear/PD#1 being right at the bullseye. They give me a good balance of attributes when done properly.

Joe

[bearfacedkiller]

I got a queen cutlery folder in D2, manix and mili in cruwear, for some reason the D2 was a ***** to get it hair popping sharp compared to the cruwear. Both with a 40 micro even the psf27 mule was easier to get it sharp, why would that be? I mean aren't the 3 very similar?

Queen runs some silly wide bevels on those knives. The ones I have seen looked thick behind the edge for a slipjoint with like a 45 degree bevel. Maybe that is where your difficulty started from, they all seem to need re profiling. I have only seen a couple though.

[bdblue]

There have been many posts here on CruWear and it is an interesting steel having been used a long time under many different names all the way back to VascoWear. In some ways it is easy to find data on it such as this

That chart makes me want more M4.

I would like to see a few other steels on that chart for comparison- 3V, Elmax and even XHP. I have an idea where they might fall. I have had good luck with D2, and I have the Manix and Military in Cruwear, so the chart makes me appreciate them more.