D-2 Steel

[Nathan the Machinist]

From crucible:
http://www.crucibleservice.com/eselector/prodbyapp/tooldie/cpm3vt.html

Unfortunatly they won't give figures for plain carbons

. .
Steel; HRC Charpy C-notch Joules
----------------------------------------
CPM 3V @ 58 113
CPM 3V @ 60 95
CPM 3V @ 62 53
S7 @ 57 165
A2 @ 60 53
D2 @ 60 28
M2 @ 62 27
CPM M4 @ 62 43

from pages:
L6 @60-68 CC-notch (J): 58
L6 @58-60 CC-notch (J): 52

D2 @59 CC-notch (J): 30
D2 @58 CC-notch (J): 30
D2 @55 CC-notch (J): 26

So yes, compared to S7, A2 or L6, D2 is pretty brittle.

Except for "high impact knives" such as a throwing knife or an axe, these impact values don't tell the entire story. These are the notched impact values, they are not the unnotched values, the torsional values, and say nothing for the actually strength of the blade. With M2 having the lowest value here, it would seem a fairly fragile steel, yet it is the best material for taps and dies, even though those are not "hot" applications. It is amazing how much abuse an M2 tap will tolerate.

Yes, the value for A2 is twice that for D2, however in practice A2 will not tolerate much more abuse than D2. I've made dies out of both. Dies are a high impact application. A2 cracks too. I like A2 because it is way easier to machine and costs less, not because it is lots tougher.

Something I don't like about their website is the abrasion resistance values, they don't seem to correlate to real world usage. I imagine some kind of cardboard slicer apparatus? The values they come up with for some of their proprietary CPM steels are very impressive. These are great steels, but the values seem a little too great.

 

[zerogee]

Well, they *are* trying to sell their premium ($$$) steels, aren't they? Never forget, they are *advertising* here - and advertising is the art of turning half truths into full blown lies.

 

[Ravaillac]

Yeah those figures don't tell the whole story, but they still are hints. Dies are a particular application too.

As for the crucible figures, an independant source would be a lot better but unfortunatly there are not too many source available for free on the Internet.

 

[Nathan the Machinist]

Yeah those figures don't tell the whole story, but they still are hints. Dies are a particular application too..

"Dies are a particular application too"

Yeah, that's true. Very true.

I have made blades out of D2 and A2. Not many, but a few.

I have have never broken a D2 knife (except for once when I did it intentionally) I have broken A2.

I'm not saying D2 is tougher. I am saying that, in practice, A2 isn't twice as tough. I don't think those impact values tell the entire story.

 

[Ravaillac]

I don't think those impact values tell the entire story.

I guess we agree on that. Thanks to my training I have some (limited) knowledge about steel and as far as I know this stuff is still highly empirica for a large part.
Actually the fact that "middle-age-like" tests like Charpy pendulum hammer are still reference tests in our modern world is pretty funny.

 

[hotrodKelley]

Ya know, re-reading my last post, it occurs to me it gives the misimpression that D2 is a good steel for taking a very fine edge. It isn't.

The two reputations that D2 has are:

1: It takes a lousy edge and holds it forever
2: it is brittle

D2 is probably my favorite steel, so I'm quick to want to defend it against these partially earned, but mostly not true reputations. But with a poor heat treat and bad edge geometry, they are true. With a good heat treat and a fine edge geometry it combines high strength (not the same thing as toughness) and good abrasion resistance to make a blade that, for me and my common uses, has better edge retention and cutting ability than anything I have tried.

Also, to say that D2 is only 1% chromium point away from being a true stainless is missing the truth a little bit. Yes it has lots of chrome, but much of it is tied up in chromium carbides (due to the huge carbon content), meaning that it does not have the stain resistance you might assume from such a high chromium steel. It is pretty good, but it ain't stainless.

The large volume of chromium carbide is a major defining characteristic of D2. This is where a lot of the abrasion resistance comes from. It is also what makes it difficult to get a super fine edge. To over come the difficulty sharpening, it is best to start with a fairly thin edge. I like a thin hollow grind. This allows a minimum amount of steel to be removed between sharpenings.

Corrosion resistance and toughness go down with higher tempers. It retains austenite at lower tempers. So I think it works best with a deep freeze as part of the quench and a fairly hard temper.

This thin, hard, high strength steels shines with a fine edge angle. That makes a great cutter with good edge retention, which is why I love it.

Makes a lousy straight razor and a even lousier thick heavy knife, and there are way better steels for making a pry bar.

Makes a good skinner, box cutter, drywall scraper, fiberglass tape cutter etc. I use it around the shop to deburr plastic and metal parts and have even hammered through small nails (don't try that with S30V)

I've heard the new CPM D2 isn't much different.

So is it brittle? I'm trying to understand, if you have a D-2, 8-10 inch bladed knife 1/4 inch thick, stock can it be used for hard use without any problems? The maker is Brend, and I know his knives are well made, I'm trying to see about the steel. I've heard stories that it is a brittle steel with blades this long, but the steel is ideal for shorter blades 4 to 6 inches. Thanks for all the help.

 

[Ravaillac]

So is it brittle? I'm trying to understand, if you have a D-2, 8-10 inch bladed knife 1/4 inch thick, stock can it be used for hard use without any problems?

Steel is not the only factor, it is a lot about how the edge is done (angle/grind), how hard the steel is run... for example Fallkniven knives, made of stainless VG-10 which despite its qualities is still stainless/relatively brittle steel, are considered robust and perfectly serviceable thanks to their convex, relatively obtuse but still sharp, edge.

 

[Nathan the Machinist]

Steel is not the only factor, it is a lot about how the edge is done (angle/grind), how hard the steel is run... for example Fallkniven knives, made of stainless VG-10 which despite its qualities is still stainless/relatively brittle steel, are considered robust and perfectly serviceable thanks to their convex, relatively obtuse but still sharp, edge.

Yeah but...

A thick, convex obtuse blade will not take advantage of the good things that D2 does (a fine wicked slicer), unless it happens to be an application where a dull, yet abrasion resistant paddle is good (digging around in mud?)

You're not getting down to that thin sharp edge where D2 shines, and you'd have a lot of carbide rich material to try to remove every time you sharpen, so you have this trade off in sharpenability where you're not getting what you traded for.

Yes, D2 is brittle when heat treated to the softer (weaker) "tough" tempers that something like 1084 does well at. D2 at HRC 58 or below gives you:

A knife with lower toughness, the impact toughness value peaks above HRC 60 and goes down where other steels go up. And in general, all steel loses strength at lower hardness. You have to temper D2 really soft before the value comes back up.

A weak edge with these great carbides that are not supported by strong martensite, so they don't get to do much of their abrasion resistance thing before the edge rolls or breaks.

To answer the question, could it be subjected to hard use without problems? Yes, unless it is heat treated improperly. But, there are other steels that would perform better for a rough and tough type knife that are also easier to sharpen. And in your application may have the same or better edge retention.

In my opinion, it is the wrong steel for that kind of knife. But I see people do it all the time, so what do I know...