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

[Cereal_killer]

This past week I was moving and I decided it was time to start using my 710, I used it hard, it cut alot of those huge HVAC zip-ties, it cut paracord that had gotten soaked in fiberglass resin, it cut ~18AWG [stranded] copper wire, rope, lots of stuff including so much cardboard than it wasn't fun anymore.

This is the outcome:





Sorry these are the best pic's I could get. I'm not good at close up photography. Also note the rust that formed in ~12 hours going from the warmth inside to the cold outside in my back pocket causing the sweat to condense and sit on the blade. To be clear the rust spots are there near the logo and run the length of the blade just above the scales when closed. (just mentioning it, not a concern).

Next up was the Spydrco GB that Fetzer85 lent me. It received the same treatment for approximately the same time. This wasn't much of a scientific test, I didn't count the number of each thing I cut and replicate it with the next, I simply used each knife for a out the same length of time doing the same tasks.

GB pictures, again sorry about quality, it's the best I can do.





You can see there is almost no edge deformation at all, it's no longer shaving but a quick strop will fix that, the 710 took an hour to fix on the SM. Also the GB was carried in the same pocket and the weather conditions were near the same, the blade was covered in condensation & sweat just the same but it doesn't have even the slightest patina.

 

[ryxlyx]

Well since the D2 is deforming rather than chipping a guy can't complain about D2 toughness here. But while according to Crucible's charts anyway M4 has an advantage over D2 regards toughness, the diff in edge retention is much greater, and is it possible that may simply be the issue here?

Can't say it couldn't have happened but if there were a HT problem, I would think that would apply to a whole batch of blade's, and not just yours.

I wonder if-- absent the cutting of copper wire-- the diff might not as great.

 

[richstag]

Dude, CPM-M4 is awesome. I don't care what anyone says. I have put mine through abuse that had really torn up previous knives.

Here is a note for D2. I gave my brother a D2 knife (quality one). We were at his place on the salt flats of the Keys and I climbed for some coconuts. His D2 got torn UP cutting one open. I have never been impressed with D2 toughness. My knife cut open another coconut with Zero damage. I believe it may just be D2 vs CPM-M4. I have not been able to chip my CPM-M4 Benchmades.

Kevin

 

[Cereal_killer]

Ok so pretty much that's just what to expect? I always had better experiences with D2, I knew M4 would be better than D2 but I guess I wasn't expecting THAT much of a difference. So just wondering, I love my 710, if I get me an M390 710 how would it compare to this GB's M4?

 

[kreole]

On those type of tasks? Won't fare as good as M4 for sure, maybe even not as good as d2 (but I wouldn't put money one way or another--that would be an interesting situation to see which is a better intersection of wear resistance (M390 wins) vs toughness (d2 wins) for those type of tasks)

 

[Cereal_killer]

Post updated & moved to general, pics added and info/pics of GB added

 

[drichardson67]

I think it would probably be worth emailing your original post to BM, and see what they have to say.

As far as steel comparison; can't say a whole lot about D2. Got bit by the powder steel bug early on in my knife obsession, so I don't have much experience with it. However, I would be quite surprised if m390 succumbed to the damage that your D2 blade did. And, of course, it has a relatively small risk of rust.

Also, when you ask about its HT, are you thinking it was too soft, and that's why it didn't hold up? Or, are you thinking it was too hard, and that's why the tip broke off? It seems as though the evidence is pointing in opposite directions. In any case, this would seem to warrant further investigation.

So, how did the tip break off?

 

[Jastab]

I carried a 710 for about a month doing hvac. The results were about the same as you posted. I havnt tried m4 yet AT WORK but I do have a Gayle bradley and m4 contego. I use a full serrated tenacious now and holy cow! The serrated edge cuts EVERYTHING!! And for being 8cr13mov it has held up amazingly good. D2 is no slouch tho, to me I like it more than s30v and vg10 for sure. I would expect the results you got given the 2 steels being compared.

 

[Cereal_killer]

Also, when you ask about its HT, are you thinking it was too soft, and that's why it didn't hold up? Or, are you thinking it was too hard, and that's why the tip broke off? It seems as though the evidence is pointing in opposite directions. In any case, this would seem to warrant further investigation.

So, how did the tip break off?

The tip broke off also cutting one of those large zip ties but it was totally my fault- I was prying it up and trying to cut at the same time, it was flush against a piece of cast iron equipment, pretty much any blade, regardless of steel, that had a fine point like the 710 would of broke. I was thinking the HT may have been too soft is why I mentioned it. The edge isn't chipped at all, all the damage is deformation and blunting. This coming week I have a few projects around the new place that should allow for some similar use with my new edge, I'll be interested to see if its any better.

I'll take your advice and email BM, I debated sending it in for lifesharpening with a note about what [I think was a small amount of] abuse caused that much damage to their factory edge but I carry the knife every day and don't really have another comparable knife so I just sharpened it myself, fixed the tip and put it back in my pocket. If I do get a chance to do any testing I'll update this thread with it. My wife said she's gonna teach me to take close up pics with our little PnS camera too so maybe I'll have better evidence next round.

 

[gooeytek]

Well-done CPM-M4 like Spyderco does is hard to beat, it's probably my favorite steel. For cutting and slicing, it's wonderful to use and touches up very easily. As for it's non-stainless designation, I haven't had any oxidation/patina issues on any of mine, and was tired of waiting for one to form on them that I just had it forced.

 

[chiral.grolim]

Y'all are talking about differences in the steel, but I haven't read any mention of blade geometry ... did I miss it?

Is the 710 blade-edge thinner than the GB? Measure the height of the edge bevel (from apex to shoulder) and thickness at the shoulder on each knife so that geometry can be compared. If the 710 is at all thinner, you are not comparing steels, only geometry. Is the Rc hardness of the 710 lower than the GB? Thinner steel is weaker, more pliable, and the same for softer steel. If the edge of the GB is more robust, you have your answer. Give the 710 the same geometry as the GB and try again. Or if the 710 steel is softer, again try giving it a more robust geometry and try again. The different chemical composition of the steels impacts corrosion resistance, abrasion resistance (i.e. dulling as material is torn away from the apex), and fracture resistance against impact. It looks like the 710 blade bent out of alignment - that is a strength issue, i.e. caused by geometry too thin or matrix hardness too low or the task. Neither of these issues suggests inferiority of steel composition, M4 at the same geometry and hardness might behave the same...

If the blades were the SAME hardness AND geometry, one wouldn't squish while the other remained straight. Rather, the more brittle steel would chip/fracture, or the less wear-resistant blade would simply wear-away at the apex... but not squish or bend out of alignment.

Until we know the geometry and hardness of each blade, this is NOT a comparison of D2 and M4. It's a comparison of a 710 and a GB.

 

[gooeytek]

I don't have a BM710, but I do have several folders in CPM-D2 and CPM-M4. I have some CPM-D2 folders that have convex edges, a hollow grind chisel, a full flat grind, etc. My convexed JYD2 with CPM-D2 is a very robust cutter/slicer but the GB with CPM-M4 just has an edge that lasts way longer despite the thin hollow grind. My GB Air with a very thin FFG CPM-M4 blade also outperforms my CB Leek which is thicker behind the edge. From my experience, CPM-M4 just outperforms CPM-D2.

 

[richstag]

Cpm-m4 would not behave the same as D2. Put the knives the same and geometry the same they would not perform the same. It's fine to try to isolate variables and remove them from this but come on.

Why would you lower hardness of CPM-M4 when the steel can handle higher? Isn't this the point?

I'm no steel junky as far as paper data but I've used D2 and CPM-M4. CPM-M4 has held up for me better with both higher hardness and thinner edge geometry.

I see a lot of more scientific testing show results that look great and I take the same steels and get chipping and damage.

When I tested Military Equipment for the DOD the point of ALSO having human testing in uncontrolled yet semi repeatable scenarios was because people happen

I get the foundation of your response and respect it but trying to say D2 and CPM-M4 are the same steel is odd to me.

Kevin

Y'all are talking about differences in the steel, but I haven't read any mention of blade geometry ... did I miss it?

Is the 710 blade-edge thinner than the GB? Measure the height of the edge bevel (from apex to shoulder) and thickness at the shoulder on each knife so that geometry can be compared. If the 710 is at all thinner, you are not comparing steels, only geometry. Is the Rc hardness of the 710 lower than the GB? Thinner steel is weaker, more pliable, and the same for softer steel. If the edge of the GB is more robust, you have your answer. Give the 710 the same geometry as the GB and try again. Or if the 710 steel is softer, again try giving it a more robust geometry and try again. The different chemical composition of the steels impacts corrosion resistance, abrasion resistance (i.e. dulling as material is torn away from the apex), and fracture resistance against impact. It looks like the 710 blade bent out of alignment - that is a strength issue, i.e. caused by geometry too thin or matrix hardness too low or the task. Neither of these issues suggests inferiority of steel composition, M4 at the same geometry and hardness might behave the same...

If the blades were the SAME hardness AND geometry, one wouldn't squish while the other remained straight. Rather, the more brittle steel would chip/fracture, or the less wear-resistant blade would simply wear-away at the apex... but not squish or bend out of alignment.

Until we know the geometry and hardness of each blade, this is NOT a comparison of D2 and M4. It's a comparison of a 710 and a GB.

 

[78LilRed]

Y'all are talking about differences in the steel, but I haven't read any mention of blade geometry ... did I miss it?

Is the 710 blade-edge thinner than the GB? Measure the height of the edge bevel (from apex to shoulder) and thickness at the shoulder on each knife so that geometry can be compared. If the 710 is at all thinner, you are not comparing steels, only geometry. Is the Rc hardness of the 710 lower than the GB? Thinner steel is weaker, more pliable, and the same for softer steel. If the edge of the GB is more robust, you have your answer. Give the 710 the same geometry as the GB and try again. Or if the 710 steel is softer, again try giving it a more robust geometry and try again. The different chemical composition of the steels impacts corrosion resistance, abrasion resistance (i.e. dulling as material is torn away from the apex), and fracture resistance against impact. It looks like the 710 blade bent out of alignment - that is a strength issue, i.e. caused by geometry too thin or matrix hardness too low or the task. Neither of these issues suggests inferiority of steel composition, M4 at the same geometry and hardness might behave the same...

If the blades were the SAME hardness AND geometry, one wouldn't squish while the other remained straight. Rather, the more brittle steel would chip/fracture, or the less wear-resistant blade would simply wear-away at the apex... but not squish or bend out of alignment.

Until we know the geometry and hardness of each blade, this is NOT a comparison of D2 and M4. It's a comparison of a 710 and a GB.

I'd be surprised if the 710 is thinner ground than the GB.

 

[richstag]

My experience too. And your comparing CPM-D2. I'm only comparing D2 for the record.

I don't have a BM710, but I do have several folders in CPM-D2 and CPM-M4. I have some CPM-D2 folders that have convex edges, a hollow grind chisel, a full flat grind, etc. My convexed JYD2 with CPM-D2 is a very robust cutter/slicer but the GB with CPM-M4 just has an edge that lasts way longer despite the thin hollow grind. My GB Air with a very thin FFG CPM-M4 blade also outperforms my CB Leek which is thicker behind the edge. From my experience, CPM-M4 just outperforms CPM-D2.

 

[chiral.grolim]

I didn't type that they were the same. I typed that this isn't a comparison of steel types if they are different hardness and geometry.

If the damage is edge flattening, i.e. a soft, thin edge deformed, and only one blade experienced it in the same use, then that blade was either thinner or softer or both, but it doesn't say anything about the composition. If blades were the same hardness, we could expect the more brittle blade (D2) to chip. It didn't. That makes me think tat the edge was softer, like the 710 is <58 Rc and the GB 63 Rc. M4 can reach higher hardness while retaining toughness. D2 can reach higher hardness as well, but toughness suffers, which is a good reason to leave it softer. If the 710 is both softer AND thinner than the GB, its relative performance is no surprise. But then it isn't comparing D2 and M4, just comparing different hardness and geometry. If the M4 were as soft and the same geometry, I'd expect them to suffer the same deformation.

 

[richstag]

WHY would you run CPM-M4 below it's peak target hardness? To me it is directly comparing steels. One outperforms the other. I get your logic it just does not agree with mine. Nice talking with you. We both said our piece. Thanks.

I didn't type that they were the same. I typed that this isn't a comparison of steel types if they are different hardness and geometry.

If the damage is edge flattening, i.e. a soft, thin edge deformed, and only one blade experienced it in the same use, then that blade was either thinner or softer or both, but it doesn't say anything about the composition. If blades were the same hardness, we could expect the more brittle blade (D2) to chip. It didn't. That makes me think tat the edge was softer, like the 710 is <58 Rc and the GB 63 Rc. M4 can reach higher hardness while retaining toughness. D2 can reach higher hardness as well, but toughness suffers, which is a good reason to leave it softer. If the 710 is both softer AND thinner than the GB, its relative performance is no surprise. But then it isn't comparing D2 and M4, just comparing different hardness and geometry. If the M4 were as soft and the same geometry, I'd expect them to suffer the same deformation.

 

[kreole]

Y'all are talking about differences in the steel, but I haven't read any mention of blade geometry ... did I miss it?

Is the 710 blade-edge thinner than the GB? Measure the height of the edge bevel (from apex to shoulder) and thickness at the shoulder on each knife so that geometry can be compared. If the 710 is at all thinner, you are not comparing steels, only geometry. Is the Rc hardness of the 710 lower than the GB? Thinner steel is weaker, more pliable, and the same for softer steel. If the edge of the GB is more robust, you have your answer. Give the 710 the same geometry as the GB and try again. Or if the 710 steel is softer, again try giving it a more robust geometry and try again. The different chemical composition of the steels impacts corrosion resistance, abrasion resistance (i.e. dulling as material is torn away from the apex), and fracture resistance against impact. It looks like the 710 blade bent out of alignment - that is a strength issue, i.e. caused by geometry too thin or matrix hardness too low or the task. Neither of these issues suggests inferiority of steel composition, M4 at the same geometry and hardness might behave the same...

If the blades were the SAME hardness AND geometry, one wouldn't squish while the other remained straight. Rather, the more brittle steel would chip/fracture, or the less wear-resistant blade would simply wear-away at the apex... but not squish or bend out of alignment.

Until we know the geometry and hardness of each blade, this is NOT a comparison of D2 and M4. It's a comparison of a 710 and a GB.

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.

 

[fetzer85]

Good stuff.

M4 and D2 will always react differently to the same type of abuse. Although both blades were subject to high force cutting, it sounds like neither blade faced high force impacts - which is where M4 could have possibly shown a sign of weakness by chipping. I think most of us expose our blades to low impact as opposed to high, in which case M4 will likely beat out D2 regardless of minor differences in blade geometry.

 

[drichardson67]

The tip broke off also cutting one of those large zip ties but it was totally my fault- I was prying it up and trying to cut at the same time, it was flush against a piece of cast iron equipment, pretty much any blade, regardless of steel, that had a fine point like the 710 would of broke. I was thinking the HT may have been too soft is why I mentioned it. The edge isn't chipped at all, all the damage is deformation and blunting. This coming week I have a few projects around the new place that should allow for some similar use with my new edge, I'll be interested to see if its any better.

I'll take your advice and email BM, I debated sending it in for lifesharpening with a note about what [I think was a small amount of] abuse caused that much damage to their factory edge but I carry the knife every day and don't really have another comparable knife so I just sharpened it myself, fixed the tip and put it back in my pocket. If I do get a chance to do any testing I'll update this thread with it. My wife said she's gonna teach me to take close up pics with our little PnS camera too so maybe I'll have better evidence next round.

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.