Cpm 3-v

G

ggoose

Joined
Apr 30, 2014
Messages
139
I have been fiddling around with CPM 3-V and, having made few knives, I thought I should test one to verify the heat treat procedure. I chopped a few 16p nails of varying diameters, and the damage to the blade may be seen in the images below. I used Crucible's procedure up to the quench, which I performed (air quench) with to very thick steel plates, and then an hour in an alcohol/dry ice bath. I tempered for two hours at 400F, which gave me Rockwells in the 64-ish range, which I thought a bit high. So I performed the second temper at 450F, resulting in Rc's in the low 60s, about 61-ish ( I had calibrated the tester and it showed accurate within the test block tolerances). My question is, for those of you who use this steel, does the damage to the edge seem excessive, or about what you would expect? I observe no chipping or cracking, just a dented rolled edge. Also, would you keep the second temper at 400F?

Thanks for any input.
gene

DSC_0850.JPG


DSC_0851.JPG


DSC_0853.JPG
 
It looks like the edge rolled/mushed. This leads me to believe that it's soft enough for hard use. IIRC 3v should be able to be a little harder than most steels and retain it's durability. The damage looks substantial but I don't have any point of reference. If the edge profile is thin enough, it doesn't matter how great the steel is, it's gonna be damaged by chopping nails. Can't really tell from the pics, is the edge pretty thin?

Nathan the Machinist works a lot with 3v and is very knowledgeable about it. His knives are very tough. If he doesn't post here I'd suggest maybe asking him about his HT process. You could also send one to Peter's and then compare it to your own HT.
 
Any steel at any hardness, ground to a thin keen sharp knife edge, will eventually "fail" one way or another when you chop/pound it through nails or pine knots or whatever. The question is not "if" it will fail, but "when" and "why" and "how".

For the sake of clarity, I will define "failure" as an edge that started out shaving sharp, and is no longer shaving sharp after doing some cutting or chopping.

The main thing to be concerned about is, how does it fail? Meaning, how radically does the edge change shape after the failure?

Dullness and flat, even bent-over spots are to be expected, and easy to fix. Minor chipping is also likely to happen when you try to cut steel or hard knots or concrete with a knife; that can be fixed by re-sharpening, too. Big chunks breaking out of the blade are totally unacceptable for a survival/camp/combat knife.

My experience abusing knives made of 3V at 58Rc and 60Rc is similar to what I'm seeing in your pics, and what I've seen in Nathan's videos. I'm pretty well convinced that you may as well go ahead and run 3V at 60Rc... the strength and edge-holding are better, and I can't see any loss of toughness.

When thin 3V edges are subjected to fairly extreme impacts against very hard materials, they often lay over/roll, but they very rarely chip out. And when they do chip/break, the fractures are quite small, and seem to be contained to a very small area. (not forming cracks that spread through the entire piece.)

The edge in your pics has clearly "failed" by rolling over/deforming, but that failure appears to only be on the specific parts of the edge that you put through a 16P nail. That's way, way better than missing a big chunk out of your edge. The rest of the blade did not fall apart or crack under that all that stress. I consider that to be a sign of a very durable knife.

I have yet to just plain break a 3V knife blade at either 58 or 60Rc, in anything resembling normal use, or in testing that I consider pretty goldang abusive. (like smacking the spine hard against a steel vise that's securely mounted to a sturdy bench.)
 
Last edited:
At that thickness (I read that as .030 directly above the edge), damage above the secondary edge bevel (in the primary grinds) shouldn't be happening. At least not with any 16 penny nails I've ever cut.

In my opinion, you're either not that hard, or you have a problem with your HT, or you got it hot while sharpening.

A temper at 400 won't normally give you HRC 64 in this steel. Are you certain about the accuracy of your hardness tester? You might be a few points softer than you think?
 
To be clear, how thick is the steel directly above the edge bevel? What was the sharpening angle? This may be perfectly normal if it's a thin knife. You haven't done a good job defining the geometry we're looking at here.
 
Nathan the Machinist said:
To be clear, how thick is the steel directly above the edge bevel? What was the sharpening angle? This may be perfectly normal if it's a thin knife. You haven't done a good job defining the geometry we're looking at here.
Click to expand...

I have re-measured the thickness where the two bevels meet and I get 0.0240 inches; that would be where the edge bevel ends and the primary bevel begins. Is that of sufficient thickness that deformation indicates a problem?
 
ggoose said:
I have re-measured the thickness where the two bevels meet and I get 0.0240 inches; that would be where the edge bevel ends and the primary bevel begins. Is that of sufficient thickness that deformation indicates a problem?
Click to expand...

I kind of think so, yeah. That's a nice thickness for a stout knife, and I've run 3V at that thickness through 16D nails without any damage reaching the grind. But, of course, that is not a scientific test. Perhaps your technique was skewed a little or your nails were harder etc.

So, yeah, I don't think that looks right, but there is only so much you can learn from chopping a nail. It's a useful test when done side by side with other controls, and it certainly makes a memorable demonstration, but in of itself it can't really determine if there is a problem unless you have another standard you can run through at the same time to compare it to.
 
Thanks Nathan. I'll keep trying. I'm familiar with your videos on the topic of comparative testing of CPM 3-V against other steels with your tweaks on the industry standard heat treat. They were my primary motivation for using this steel. If you wouldn't mind, does it sound as if this procedure is generally headed in the right direction:

Foil-wrap and heat to 1975º F; equalize for ~30 minutes.
Rapid plate quench in foil until cool to touch. Remove foil.
Sub-zero immediately. Temper twice at 400º F for 2 hours.

This was yielding mid-60s Rc, but I will recalibrate my tester.

Thanks again,

gene
 
I think that sounds good. Yes, recalibrate your tester. But, regardless of the hardness reading you get, try cutting a nail after that and see what happens?
 
You must log in or register to reply here.
Back
Top