D2 vs. M4 comparison at some typical harder use cutting tasks

drichardson67 said:
I think I get the arguments about comparing apples and oranges, blade geometries, etc... But the question to me remains: why would a blade, with only an hour of real, but not overly abusive, use, both blunt and deform...AND break.

If there were problems with the HT, maybe one could expect chipping and/or a break OR blunting and deformation--depending upon whether it was too hard or too soft. But both simultaneously??? This is the curiosity of the matter to my mind. And I can't imagine how to account for it. Even when prying against cast iron, when the fulcrum is a non-stationary plastic zip tie, the tip of a D2 Benchmade should not fail. Especially when the blade suffers deformation cutting the same plastic.

Probably I've oversimplified, and I don't want to downplay other variables, about which I understand little, but the information about this particular blade just doesn't stack up IMO. It both deforms and breaks, in an hour of, what would be for me, normal use.

This to me points to something peculiar to the blade: be it (uneven?) HT issues, problems with the steel at the forge, I don't know.. But these two information sets I don't think should so easily co-exist under the given circumstances. Why they do should be the first question.
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You're always going to find a mix of deformation and chipping in extended hard use like that. That is not surprising. They happen separately, and also one can lead to the other.
 
kreole said:
Damage is occurring at the edge, not above it. If the edge angles are the same, then they're the same 'geometry' (thickness and angle) until the top of the least high one--so past where the damage is. The only way geometries above the edge effect edge damage is in how it alters how the user cuts differently with the knives.
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Yes, everything in my post regarded the edge. No mention was made as to edge angle of either blade. By measuring height of the edge bevel and thickness at the shoulder, we can calculate edge angle and even produce a magnified diagram of the geometry of each. The damage seen is edge-flattening that appears due not to abrasion or chipping but 'squishing' i.e. a problem of strength. Strength is directly related to material hardness (Rc) and thickness. If I am right about the damage then the 710 is either thinner or softer than the GB, or BOTH.

Now, if they are the same geometry, or if the GB is actually thinner, we know that the issue is material hardness. CPM-M4 can be taken harder than D2 without losing as much toughness, something that makes it superior. IF the M4 were as soft as the D2, it would fail the same. But I agree with what was posted above, why would anyone leave it softer (i.e. weaker) than necessary? IF the D2 were as hard as the M4, it still might not have failed or it may have chipped-out - that is a good reason to leave it softer but also demonstrates its inferiority. However, all of this assumes that the blades are indeed the same geometry and that the D2 was as hard as it could be without suffering chips. Both of these assumptions may be false. Without further information, the comparison is NOT between the steels but between two knives that might as well be of the same steel. That's all.

And in response to another post above, "minor" changes in apex geometry and also in 'finish' (coarse vs fine grit, etc.) can have HUGE consequences in apex performance/failure, as can matrix hardness. A change in chemistry is the last consideration to make as its effect is easily masked/superseded by these others in "tests" as rough as described in this thread.
 
The Gayle Bradley has a very thin geometry in both the blade and and edge. I don't have a 710 anymore, but I would expect it to be more obtuse. And I would expect Benchmade's D2 to be considerably softer than Sypderco's M4.

However, M4 is much tougher than regular D2, but a little less tough than CPM D2. M4 also holds an edge much better than both types of D2.

There are a lot of factors that play a role, as has been pointed out, and we don't have enough information to attribute how each factor plays a role. Nonetheless CPM M4 is seriously good steel, and I'm sure that the differences in steel play a big role here.
 
Twindog said:
The Gayle Bradley has a very thin geometry in both the blade and and edge. I don't have a 710 anymore, but I would expect it to be more obtuse. And I would expect Benchmade's D2 to be considerably softer than Sypderco's M4.

However, M4 is much tougher than regular D2, but a little less tough than CPM D2. M4 also holds an edge much better than both types of D2.

There are a lot of factors that play a role, as has been pointed out, and we don't have enough information to attribute how each factor plays a role. Nonetheless CPM M4 is seriously good steel, and I'm sure that the differences in steel play a big role here.
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Where did you read that CPM D2 is tougher than CPM M4 and tougher than D2?
 
kreole said:
You're always going to find a mix of deformation and chipping in extended hard use like that. That is not surprising. They happen separately, and also one can lead to the other.
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I know I'm a relative newby, but it is curious to me that D2 would fail in both respects in only an hour of moderate, even hard, use. It wasn't extended use. So, yes, Cereal Killer, it should have held up better, and, to my mind, in respect to BOTH deformation and chipping. IMHO, that peculiar blade is sub-par.

I'm curious, of those cutting tasks, which do you think was hardest on the knife: the zip ties, the resin soaked paracord? I can see 18 gauge stranded copper wire dulling a knife, but not deforming it. To what do you attribute the deformation? Were you by any chance watching that at all while using it?
 
kreole said:
You're always going to find a mix of deformation and chipping in extended hard use like that. That is not surprising. They happen separately, and also one can lead to the other.
Click to expand...

I know I'm a relative newby, but it is curious to me that D2 would fail in both respects in only an hour of moderate, even hard, use. It wasn't extended use. So, yes, Cereal Killer, it should have held up better, and, to my mind, in respect to BOTH deformation and chipping. IMHO, that peculiar blade is sub-par.

I'm curious, of those cutting tasks, which do you think was hardest on the knife: the zip ties, the resin soaked paracord? I can see 18 gauge stranded copper wire dulling a knife, but not deforming it. To what do you attribute the deformation? Were you by any chance watching that at all while using it?
 
nccole said:
Where did you read that CPM D2 is tougher than CPM M4 and tougher than D2?
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I saved a graph to my computer for quick reference, but didn't save the source. Here's a screen shot of my computer.

DSC01993_zps57bd6351.jpg
 
Twindog said:
I saved a graph to my computer for quick reference, but didn't save the source. Here's a screen shot of my computer.

DSC01993_zps57bd6351.jpg
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I would like to know where that came from, and more in general about how that info was tabulated. I don't think I have ever seen a bigger jump in any category that high just from the PM process. That graph with its unit-less numbers is saying that CPM D2 is more than twice as tough as D2. I don't buy that. Not questioning you, but that looks like a very vague chart that I would not trust. It should give some units, and have some explanation as to what it means, and how and what method the results were obtained. There are very scientific tests that are done to get numbers and comparisons.

*Just noticed that the idiot (yes, I am now calling him an idiot, and not just questioning the accuracy) that made the chart has "CPM 154CM" listed as a steel. That is not a steel made, and the credibility, what little was there, is now gone. Plus it is shown as tougher than CPM M4 and CPM D2. I highly doubt that. I would't trust or use that chart to base any information off of moving forward.

I appreciate you backing up your claims, I was not trying to bash you, just legitimately curious as something sounded fishy.
 
Just wanted to update this, my contact at BM (Nolan Kidwell) has asked I send the knife in and the pictures of the damage, and a detailed description of the damage. I emailed over the weekend and received the reply 10 minutes after they opened this morning. They will be Rockwell testing it and just generally evaluating it. I will update here with what they do/say.

Thanks again and feel free to continue this conversation that is now above my level of understanding, I'm enjoying learning and reading what you gent's have to say.
 
drichardson67 said:
I know I'm a relative newby, but it is curious to me that D2 would fail in both respects in only an hour of moderate, even hard, use. It wasn't extended use. So, yes, Cereal Killer, it should have held up better, and, to my mind, in respect to BOTH deformation and chipping. IMHO, that peculiar blade is sub-par.

I'm curious, of those cutting tasks, which do you think was hardest on the knife: the zip ties, the resin soaked paracord? I can see 18 gauge stranded copper wire dulling a knife, but not deforming it. To what do you attribute the deformation? Were you by any chance watching that at all while using it?
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I didn't pay attention as it was happening but just by which of those tasks took the most effort I'd say either the copper wire or the resin soaked paracord, the zip ties were a relatively small part of the overall job.

I'm not discrediting any one else but your opinion makes the most sense to me (but it's also pretty much 100% agreeing with me). Again not discrediting anyone else, I don't personally know enough to know what's right and what's wrong. Thanks again everyone.
 
nccole said:
I would like to know where that came from, and more in general about how that info was tabulated. I don't think I have ever seen a bigger jump in any category that high just from the PM process. That graph with its unit-less numbers is saying that CPM D2 is more than twice as tough as D2. I don't buy that. Not questioning you, but that looks like a very vague chart that I would not trust. It should give some units, and have some explanation as to what it means, and how and what method the results were obtained. There are very scientific tests that are done to get numbers and comparisons.

*Just noticed that the idiot (yes, I am now calling him an idiot, and not just questioning the accuracy) that made the chart has "CPM 154CM" listed as a steel. That is not a steel made, and the credibility, what little was there, is now gone. Plus it is shown as tougher than CPM M4 and CPM D2. I highly doubt that. I would't trust or use that chart to base any information off of moving forward.

I appreciate you backing up your claims, I was not trying to bash you, just legitimately curious as something sounded fishy.
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Yes, you're making good points. Thanks for that. I wish I remembered where I got that chart.

Here's one directly from Crucible:
http://www.crucible.com/pdfs/SelectorKnifePocketRotatedCrucibleLLC.pdf

The scales are different than the chart I posted, but the basic information is roughly the same, but not entirely. Crucible shows that CPM M4 is much more wear resistant and tougher than D2, but CPM D2 is equally as tough as M4, though not as wear resistant.

154 Cm is less wear resistant and less tough than CPM 154.
 
To get back to Cereal's problem with his 710 D2 blade not performing as well as his GB M4 blade: The biggest issues seems to be deformation of the D2 edge and, probably, increased wear on the edge, not chipping.

Deformation is an issue with strength, not toughness.

Strength is a function of hardness and it shows up as resistance to deformation.

Toughness is a resistance to breakage, cracking and chipping.

So the issue here is with strength, not toughness.

D2 is almost as tough as M4 and powdered D2 (CPM D2) is equally as tough as M4. So we wouldn't expect a dramatic difference in toughness, which we don't see because we don't see an increase in chipping.

M4 is almost always run harder than D2, so there is likely to be a difference in strength, with M4 being stronger. That difference would show up as deformation, which it does here. I'd guess that the GB is run 2 or 3 points harder than the 710.

M4 also has a big advantage in wear resistance, which is hard to see in the photos, but probably present.

I'm not ignoring Chiral's point about geometry, but I believe that geometry differences between the 710 and the GB are not likely to support the problems we see. But differences in the steel do support the problems we see.
 
Cereal_killer said:
Just wanted to update this, my contact at BM (Nolan Kidwell) has asked I send the knife in and the pictures of the damage, and a detailed description of the damage. I emailed over the weekend and received the reply 10 minutes after they opened this morning. They will be Rockwell testing it and just generally evaluating it. I will update here with what they do/say.

Thanks again and feel free to continue this conversation that is now above my level of understanding, I'm enjoying learning and reading what you gent's have to say.
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That's good news. I'm sure BM will treat you well. And I'm very curious about what they'll find out.

I'm with you. I enjoy these types of threads most...it's where I learn the most. Thanks everyone.
 
The best part of this thread is that their are many different views and opinions but NO sarcasm and childishness.
Thank you all for that as I have always wanted to know more about steels, and this has been a very informative conversation.
Thank you all again and please keep us updated as to what Benchmade finds.
Frank.
 
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