D2 vs. CPM-D2 vs. A2?

james terrio

james terrio

Sharpest Knife in the Light Socket
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Apr 15, 2010
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Does anyone have some experience or info (Charpy notch tests, etc.) on the relative toughness of regular D2 compared to the CPM version? I know a little about the CPM process and how it generally makes the alloy more consistant overall, but for the purpose of this thread I'm concerned specifically with toughness.

The reason I ask is, I'm looking to make some tool-steel knives in the 4-6" long, 3/16-1/4" thick blade range, intended for fairly heavy-duty survival/combat use. I have both D2 and CPM-D2 on hand, but after more study I'm beginning to think A2 might be a better choice... according to the charts I've found A2 has a lot higher toughness, comparable to O1 and CPM-154 (both of which I like very much). Not as much edge retention as D2 of course, but I'd rather offer a knife than can be sharpened in the field over one that might break if you pound on it.

Thanks in advance for your thoughts!
 
I haven't done any apples to apples comparisons of D2 vs cpm D2, but my general impression is that CPM D2 will stay sharp longer than regular D2 in abusive applications, but regular D2 holds an edge just as well in "regular duty" applications and also cuts things like hide better than the CPM version, probably due to the toothy nature of the larger carbides.

I like the big carbides if the heat treat address D2's issues with edge stability.

One has to keep in mind the context when discussing "better edge retention". While D2 (when it is done well) will outpace most other steels in many edge retention tests, a lower carbide steel like A2 or O1 will often beat D2 in edge retention when abrasion resistance isn't a factor, such as chopping and prying with the edge.

For your application, personally I would chose A2, unless corrosion resistance is a factor.
 
Nathan the Machinist said:
While D2 (when it is done well) will outpace most other steels in many edge retention tests, a lower carbide steel like A2 or O1 will often beat D2 in edge retention when abrasion resistance isn't a factor, such as chopping and prying with the edge.

For your application, personally I would chose A2, unless corrosion resistance is a factor.
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Thanks Nathan, that's about what I was thinking but I always like to ask folks with more experience than I have. I've read many of your posts about HT for D2 and have learned a lot.
Corrosion resistance isn't a factor at all for the purposes of this discussion.
 
I saw a chart from a steel company(Timkin I think) that put O1 just slightly above A2 for toughness at same hardness. To me it makes sense due to the fine carbides in O1 and fewer of them. A2 would have a longer lasting edge. Of course, D2 would have even a longer lasting edge. Big carbides will have a different quality to the edge. If there is a metalurgist on site let me know if I am wrong.

David
 
If there any metallurgists reading this thread, could you recommend a book that is the equivalent of "The Complete Idiot's Guide to Metallurgy"? I was a life science major, but find the discussions of steel characteristics in knives fascinating.

Regards,
Tim
 
Mr. Gregory - I feel like you're ignoring me :/

Also, that is a great suggestion, especially for folks who can't shell out the dollars for the heat treater's guide.
 
Matthew Gregory said:
Not a metallurgist, but this one helped me greatly:

Heat Treatment, Selection, and Application of Tool Steels
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My thoughts, exactly, Matt. Great introductory book.

As to the specific choice, I would add that the geometry of the knife blade probably has as much influence on steel choice as the actual type of steel. CPM D2 should be tougher than D2, A2 will be the toughest. But, in a 4-6" blade, at the thicknesses listed, it should be no problem to make a knife out of any of these steels that is tough enough to stand up to abuse.
 
Matthew, thanks for that link. I've heard many folks I respect recommend that book, but this is the first time I've read any of it. It looks intriguing and no-nonsense. :thumbup:

EDIT: the glossary alone is worth copy/pasting for reference!

RJ Martin said:
As to the specific choice, I would add that the geometry of the knife blade probably has as much influence on steel choice as the actual type of steel. CPM D2 should be tougher than D2, A2 will be the toughest. But, in a 4-6" blade, at the thicknesses listed, it should be no problem to make a knife out of any of these steels that is tough enough to stand up to abuse.
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I agree completely. I suspect that given the same geometry, the differences between the alloys we're discussing would be fairly small and any of them would serve pretty well. Most users might never notice the difference in toughness.

But I'm a cantankerous sort and I just plain enjoy sorting through this kind of thing, looking for that little "edge" that can make a knife better :)
 
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Oh, but I think it does matter. Whether is it 3/32" and 4" long, or 3/8" and 15" long, the toughness of the edge will effect edge retention depending on the use.

Excluding macro level toughness issues like breaking/chipping out the blade, the steel and heat treat are still important in any rough use blade. In a thin precision slicer like a skinning knife I'd use D2 because it will hold its edge longer in that application, but in a knife expected to hold an edge while hacking through wood and prying open nuts etc I'd go for A2 for better edge stability in rough use.

Of course, geometry is a very important factor as well.

...just my .02...
 
Of course it matters or I wouldn't have asked in the first place :) Heck if I didn't care about learning which steels are suited for different applications, I'd just buy pre-made blades, slap some handles on them and change my nickname to Monkey Boy :D

In all seriousness, I do appreciate all you guys' help and I feel we're coming to some pretty clear conclusions... A2 is better for this type of blade. D2 is better for thin precision slicers.
 
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