AUS8 better edge retention than M4?! UPDATE: page 3

knarfeng said:
The most likely explanation is that you put a wire edge on the GB when you sharpened it.

CPM M4 will outcut AUS8 any day of the week and twice on Sundays.
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Ditto... Unless cutting is done in extremely corrosive environment 100% of the time, I can't imagine AUS8A out-cutting M4 at any edge thickness.
 
Ok so I resharpened the knife and started cutting again. The edge is 42 inclusive, by the way.

I made probably 60 cuts into cardboard, and many more cuts into various materials. I noticed that this time there was way less edge deformation, and it stayed sharper also.

I did notice that the edge felt toothy after the first few cuts though, and looking at the edge at 60x confirmed that. The edge looks like tiny little chips were taken out all along the edge. They are barely big enough to feel with your fingernail, but they are definitely there.

I noticed that as I kept cutting, the toothiness almost smoothed out to a point, and even after doing a lot more cutting that toothy edge didn't seem to get much duller. So pretty much what I think I'm seeing now is a very fast degradation of the hair whittling edge, but after that initial super sharp edge is gone I'm left with a reasonably sharp edge that seems to last a very long time. By reasonably sharp I mean that it will slice phone book paper, but barely shave hair.

I hope this makes sense. As of right now I'm not going to send it back, unless y'all think I need to.
 
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spydusse said:
No,you should still send that back
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Agreed. Properly heat-treated CPM-M4 has shouldn't start feeling toothy after a few cuts through normal cardboard (assuming that the problems aren't due to a wire edge or some other sharpening issue).
 
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I had similar happen with S30V. It took six full-on rebevels before the edge stopped microchipping while cutting cardboard.
 
hardheart said:
I had similar happen with S30V. It took six full-on rebevels before the edge stopped microchipping while cutting cardboard.
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I had many experiences like that with production folders in S30V. Once with VG-10 but never with many other cheaper low-end steels... You think the factory sharpening may somehow weaken the outer edge on this type of steel? (too fast and hot?)
 
I'd definitely send it back. M4 is a great steel, and should hold a shaving sharp edge for longer than what you're dealing with. When I first tested out the steel, it simply amazed me. Outcut my S30V, D2, 440C, 154CM, VG-10 and 1095 knives by a very large margin (on wood and cardboard). I know that there are other steels that have better edge holding abilities, but CPM-M4 is definitely one of the best.
 
Thanks for the info guys. I'm a little disappointed but I'll call spyderco tomorrow and start the warranty process.

Will I get a new knife back or a refurb?
 
The edge wear you are seeing and the way its happening is how pretty much all PM steels work. The carbon type PM steels like CPM-M4 & CPMD2 are steels that will have the most liked edge characteristics because they hold a sharp feeling edge longer and are easily brought back to sharp with a ceramic rod or strop. Stainless CPM steels often get a bad rap because they loose their sharp edge even faster and are not as easily brought back to razor sharpness.

I don't see any problem with this type of edge wear and to me its the way it should work. Phil Wilson describes his experiences in the XHP thread and they seem identical to mine. I think its just because really good steels are not something everyone is accustomed to so some initial misunderstanding occurs.

Try changing your bevel geometry too, with over a 40 degree bevel your not really taking advantage of the steel. Its also causing you to use more force in your cut and create more pressure on the edge= more wear. Try a 13-15 degree main bevel and a 20 degree micro starting no lower than 1k grit. This will reduce the pressures on the apex of the edge and increase cutting performance without sacrificing durability.
 
Ok I can subscribe to the idea that this is normal wear, I just thought it should stay sharper than it was in relation to how much cutting I did. I mean don't get me wrong, it was sharp - just not really that sharp. It would in fact shave hair, barely, and it was not hair popping at all.

Again the micro chipping wasn't bad enough to be heard on the UF sharpmaker rods (like it was the first time, it sounded like ice cracking); but I could see it clearly at 60x.

I've heard before that these particle metallurgy steels will react differently when cutting, but this just took me by surprise.



knifenut1013 said:
The edge wear you are seeing and the way its happening is how pretty much all PM steels work. The carbon type PM steels like CPM-M4 & CPMD2 are steels that will have the most liked edge characteristics because they hold a sharp feeling edge longer and are easily brought back to sharp with a ceramic rod or strop. Stainless CPM steels often get a bad rap because they loose their sharp edge even faster and are not as easily brought back to razor sharpness.

I don't see any problem with this type of edge wear and to me its the way it should work. Phil Wilson describes his experiences in the XHP thread and they seem identical to mine. I think its just because really good steels are not something everyone is accustomed to so some initial misunderstanding occurs.

Try changing your bevel geometry too, with over a 40 degree bevel your not really taking advantage of the steel. Its also causing you to use more force in your cut and create more pressure on the edge= more wear. Try a 13-15 degree main bevel and a 20 degree micro starting no lower than 1k grit. This will reduce the pressures on the apex of the edge and increase cutting performance without sacrificing durability.
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I think calling them super steels tends to give the wrong impression of how they will work. It creates the thought that they will stay sharp for a longer amount of time and they do but not in the way expected.

Materials like cardboard can be really tough on a edge and if you made over 50 cuts and still had a "sharp" edge I'd say the edge was performing well. Once the edge reaches the plateau where not much seems to happen is the point I've never been able to get past. You'd probably need to make over 1000 cuts in cardboard to see what that knife could really do.
 
aus 8 is a decent working steel but not in same league as m4. chrominum carbides cannot start to compete with vanadium & tungsten carbides in edge durability. i'm certainly no metallurgist but to predicate aus8 as anywhere close to m4 would negate many basic tenants of atomic structure. maybe "Mete" will help clear the fog . he is a working metallurgist for over 20 years.---dennis
 
Yesterday I've been cutting thick electric cords with the GB for over an hour, and it still shaves the hair off my wrist. The edge feels totally smooth. There is no need to do anything to it.
This is my first CPM M4 blade, and it performs as I've come to expect after all the insane praise it got and still gets, in other words, it performs beyond any steel I've ever seen.
Yours must be a dud.
 
Dennis , '20 years' ? I've been a metallurgist so long I finally retired !!
I used a CS Master Hunter in AUS-8 for a number of years and it's an excellent knife steel. However CPM M4 is a different creature with much higher wear resistance due to the harder and more numerous carbides .One of the comments was the need in his blade to resharpen a few times to remove the problems. This is due to damage to the steel buy factory grinding [overheating] .More common than it should be !! Second possibility is improper HT. Third is the user sharpening . What are the sharpening angles from various makers ? I have a knife that had the tip ground to 40* and it made for poor dressing out and skinning a deer. I wouldn't like a knife with more tha a 30* angle !
Unfortunately I don't have a CPM M4 knife to compare to.
 
M4 shouldn't be rolling at 62.5 HRC at all so if it does then there is a problem.
 
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