is CPM-D2 worth the expense?

[James_Terrio]

I'm working on a couple of stock-removal field knives, using 3/16" D2 from TKS. I'm a big carbon steel fan but I chose D2 because I don't have any HT equip. This way I can grind 'em out and send 'em to TKS for HT. (or somewhere else if you guys have better recommendations) I've already decided to spring the extra couple bucks to have them cryo treated as well; I want them to be tough since they're intended for field/survival type use, folks tell me cryo helps.

My question is this: looking at the vast difference in price between D2 and CPM-D2, can someone justify this for me? Would I need to have a specialized HT done to it to make it worthwhile? If it really makes a better blade I can probably be talked into it. But at double the cost.... yikes. I don't want to be a cheapskate, I just want to make an informed decision.

One more dumb question; Admiral lists their D2 for about $105/3'... is this CPM-D2? I ask because TKS only wants around $75 for 3' of what they list as CPM-D2, their "regular" D2 lists for $13/1'.

I'm also thinking about trying some A2 for similar knives, any comments? They will all be 5" or less blades, flat or convex ground, meant for camping/hunting/survival. Low likelihood of breaking is my big concern, edge retention and corrosion resistance are nice but not my biggest priority.

Thanks much for your help, gentlemen.



JT --- formerly known as GibsonFan

 

[SDS]

Heat treated properly I wouldn't worry about chipping or breaking. I love using D2 and it's a tough steel. Here are some "abuse" pictures I took while testing a prototype for a swat team.

This is regular D2. I don't know if the CPM is worth double the cost. Others here would be better qualified to answer that one.

SDS

 

[James_Terrio]

Thanks SDS, that's a reassuring pic of it not chipping Is it safe to assume you HT'ed that at the standard specs, or do you have a trick up your sleeve?

 

[blgoode]

I guess I'd find out first what the CPM differs in. ISnt it supposed to polish up better? I dont polish so I'm sticking with regular D2 I guess

PM NWA
http://www.bladeforums.com/forums/member.php?u=155705

he will beat their pricing.

 

[James_Terrio]

These will be given a hand-satin finish, so "polishability" isn't really an issue.

 

[SDS]

James, if I were a marketing genius I'd probably claim that I have a super top secret magic formula that I discovered deep in the caves of a foreign country. This "magic bullet" allows me to get every ounce of performance out of this steel and it's my own personal secret that I'm not telling.

Truth is the only thing I did differently on this blade than others I have done is that I added one extra tempering cycle (for a total of three). Thats it. No magic bullet. No secret formula extracted from those south American aboriginal cave dwellings deep in the siberian jungle. Sorry.

SDS

 

[James_Terrio]

No magic bullet. No secret formula... Sorry.
SDS

Don't be sorry, that's what I was hoping to hear I don't really trust hype and "secret formulas" and whatnot.

Must not be awake yet... it took me a minute to realize that there's very few jungles in Siberia! I guess that's how they keep it a secret...

 

[House Knives]

Save your money..there are several thing you said about D2..D2 is an airhardning steel so who ever is doing your HT make sure the know wha they are doing..D2 is a steel that really does not gain much with Cryo save save your money on that also.

D2 is a great steel and it is my favortie,as for the CPM D2 if I am going to buy high dollar steel would be 3V or CPM 154..

D2 has been around for a long time and there is a reason for it

 

[mete]

The carbides in D2 are large and it produces a rather coarse edge. The CPMD2 has finer carbides and thus is capable of taking a finer edge.

 

[Danbo]

I really like CPM D2. I find it easy to work with and it takes a finer edge than regular D2.

 

[James_Terrio]

How much finer of an edge? I'm not trying to be a smart-alec, honest But if we're talking a 10% increase in one factor of performance at a 100% increase in cost, I just can't see it. Maybe I am a cheapskate
The carbide thing makes sense to my rather fuzzy understanding of steel... does that help toughness too? For the kind of knives I have in mind, toughness is more important than a super-fine edge anyway. (I may be misusing the term toughness but bear with me. You know what I mean in a general sense.)

House Knives, I took a brief look at the Crucible Metals chart on 3V, it looks pretty cool, but I really need to stick to the basics. I was surprised how long D2 has been around. Anyone else have a comment on cryo for D2?

Thanks again for your help fellas.

 

[Dan Pierson]

The carbide thing makes sense to my rather fuzzy understanding of steel... does that help toughness too? For the kind of knives I have in mind, toughness is more important than a super-fine edge anyway.

Finer and more uniform carbides should improve toughness by reducing potential fracture points at the microscopic level. The question is by how much do they reduce toughness? I'll happily defer to the experts on this one.

 

[James_Terrio]

Finer and more uniform carbides should improve toughness by reducing potential fracture points at the microscopic level. The question is by how much do they (I think you meant improve) toughness? I'll happily defer to the experts on this one.

Right, exactly. One of the reasons I picked D2 for these knives is that's it's so well-known. So I bet some folks will be able to quantify that at least somewhat.

 

[mete]

It's the transverse impact strength that improves the most .That's good for a blade. But on a practcal level I couldn't say as it's difficult to exactly relate Charpy tests to actual use.
As for the finer edge that depends on what you will use the blade for.

 

[galadduin]

I often polish D2 to mirror finish, it is awkward for some but I really like the "peel" effect, when seen in an angle it is great to see those structures in steel, reminds me wootz...

 

[James_Terrio]

As for the finer edge that depends on what you will use the blade for.

And of course, it depends on what we mean by a fine edge. These will be field/bushcraft/survival/camp knives. Not scalpels, but not pry-bars either. I think it's reasonable to expect them to shave hair and not chip out in the brass rod test. Y'know, typical Wilderness & Survival Skills type stuff.

I thank you all for your help in this conundrum! As for the cryo question, I haven't yet found much info on it so I guess the thing to do is have a couple cryo'ed and a couple not, and compare 'em. But if any of you have more info, please pass it on

I often polish D2 to mirror finish, it is awkward for some but I really like the "peel" effect...

Weird how different steels look with the same exact finish, eh? For some reason tempered-back Nicholson files look really pretty to me when ground into blades and hand-rubbed to 1000-grit. There's a sparkle and color in there that some steels just don't have. As for the D2, I reckon I'll just have to polish some up and see if I like it.

 

[Nathan the Machinist]

I thank you all for your help in this conundrum! As for the cryo question, I haven't yet found much info on it so I guess the thing to do is have a couple cryo'ed and a couple not, and compare 'em. But if any of you have more info, please pass it on

With a good heat treat, regular D2 can be taken to an edge that will pop hairs in mid hair without much trouble. It can also retain a shaving edge after skinning several deer. Try that with most knives. And D2 continues to cut flesh well after it is dull because of those carbides. I have a smooth steak knife made of it that cuts well almost like a serrated steak knife, even though it has been dulled from many contacts with hard plates.

I think it helps fine edge stability to remove retained austenite. One way is to use high temperature tempers to decompose it. Another it to use a cold treatment. One advantage to using a cold treatment is you can stay in the lower temper ranges associated with better corrosion resistance and possibly finer or less precipitated grain boundary carbides. Does that sound right Mete?

I have found, with D2, that a snap temper is not necessary before a cold treatment and it may reduce the amount of austenite that converts. For that reason I use cold as a part of a continuous quench. Dry ice and acetone work well and may reduce brittleness issues one can get into with a dunk in LN.

I like the large carbides in D2 in my knives, but it is important to soak it a good long time or they'll be very large and your martensite will be carbon lean. Also, if you're using a cold treatment, don't be afraid of the higher austenitizing temperatures. D2 will never be a super fine grained steel, and a trip to 1850 or even 1900 isn't going to change it. I feel 1800 is not hot enough to free up enough carbon or chrome. My opinion, but I'm just a dumb machinist.

 

[Will Leavitt]

One of the guys that taught me to make knives (or at least tried to teach me ) has pictures of his D2 field knives with a jack stand under the but and the tip and his trucked jacked up on a bottle stand on the ricasso. A picture is worth 1000 words.

 

[mete]

Nathan, it still depends on the use.When I used to do woodworking and woodcarving I wanted a very fine edge.A field does not require a fine edge. That will depend on carbide size for the most part [CPM !].
The next part is to maximize performance of the matrix. Dissolve as much carbide as possible in HT. That may be by normalizing at high temperature ,1900 F,Followed by a lower hardening temperature. That lower hardening temperature lowers the RA and further reduction of RA can be made by cryo. Snap tempers should be 300 F, higher will stabilize some of the RA.For knives I don't see the need for high tempering temperatures, stick to 400 F for the complex steels.
Fine edge ?- small carbides [CPM], minimum RA, Martensite saturated with carbon,fully hardened [400F temper].

 

[Nathan the Machinist]

Snap tempers should be 300 F, higher will stabilize some of the RA.For knives I don't see the need for high tempering temperatures,.

That is a fact.

I have two identical D2 blades here, both measure HRC 62. Both had LN cryo. One had a "snap temper" first that went to 400F for an hour. They were both given the same acute edge and subjected to the same whittling cuts. The difference is hard to believe. One, the edge damage can be seen at an arms length, the other still shaves hair. The snap temper before cryo must have stabilized some austenite, because even though it Rockwells the same, it ain't.

Avoid retained austenite in your D2. One way to be sure you achieve this is to go directly into cryo without pause. This blade went from 1850 to room temp to -300 as one continuous quench. It then tested HRC 67. It was tempered twice at 450 to bring it down to HRC62. And it isn't brittle as a result of no snap temper. I just got up and went out into the shop and hammered it through a nail (try that with something like a Mnandi some time). The very acute edge does show some minor damage, but it didn't chip or crack or anything. It is tough and it holds a great edge.