CPM 20CV — rolling

Jay2021 said:
Hello everyone, happy holidays. I was cutting almond brittle last night (no joke) with a brand new folder made with CPM 20CV and the knife tip rolled…in a matter of seconds it went from a nice pointy tip to dull. Has anyone else ever had bad experiences with this steel and with it rolling so easily? I expected a lot more from it to be honest, especially since it's a made in the USA knife that cost me around $120. Otherwise, I have no complaints with this steel...this folder was easily one of the sharpest out of the box I've ever received and it cuts like a charm. Please let me know what you guys think and how you'd fix it--sharpening, stropping, etc. Thanks!
https://imgur.com/a/BYyuQAb

Revised: here's the infamous almond brittle, which is excellent and actually not at all that hard when you bite into it.
https://imgur.com/L6d5NUB
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Edge geometry is the most important aspect of tip strength, knife can be made out of the best steels with the best heat treat, but if its sharpened too thin, it'll chip/roll like pot metal.

You'll have to re-sharpen it to fix that tip, if you want it sturdier, put a bigger angle on the edge.
 
kreole said:
Looks almost exactly like the S110v Para 3 I got and accidentally bumped the tip on the countertop a day or two later (putting it down, not even cutting anything 😒)

C4n8VHR.jpg


I used ceramics to get it back in shape/remove the bent over part and continue to use it as is for now. It'll sharpen out fine first reprofile.
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S110/M390/20CV are all not great in toughness. I broke the tip off on my Borka M390 tanto when I dropped it on the floor, it had a beefy tanto tip too. Was not good times.
 
Better rolling than chipping. 😁
You can fix a rolled edge with a dry leather strop, or a butcher's steel that doesn't remove any metal.
A ceramic rod, bottom of a coffee cup, top of a car window or sharpening stone will ask take care of the roll, but at the cost of blade meta!.
 
Something else to consider, as it was touched on earlier, is the apex.

There is VERY little steel at the apex, which if ground with a power tool, can heat up extremely fast.

Belt grinders tend to create a bit of a convex, which can alleviate this issue a bit if worked slowly and with constant water drenching.
 
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Chronovore said:
The steel in your blade is heat-treated to have specific properties. Grinding dry with a power tool can sometimes create high heat right at the surface. It can be enough to diminish those properties right at the surface.

I don't know enough to say why this tends to happen at the factory grinder but not so much with home systems. I just know that it happens. This is why some people in this thread have reported issues with factory edges that tend to go away after sharpening past that surface layer. This is also part of why edge retention results tend to pick up with subsequent edges in controlled cut testing.
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Interesting. Thanks for your input. Hopefully once the factory edge is sharpened off the tip will have better edge retention.
 
Cassull said:
Edge geometry is the most important aspect of tip strength, knife can be made out of the best steels with the best heat treat, but if its sharpened too thin, it'll chip/roll like pot metal.

You'll have to re-sharpen it to fix that tip, if you want it sturdier, put a bigger angle on the edge.
Click to expand...
Good point. Thanks for your input. This knife was sharpened very thin, so it was probably doomed to being rolled sooner than later. When I sharpen it again I'll consider putting a bigger angle on the edge.
 
afishhunter said:
Better rolling than chipping. 😁
You can fix a rolled edge with a dry leather strop, or a butcher's steel that doesn't remove any metal.
A ceramic rod, bottom of a coffee cup, top of a car window or sharpening stone will ask take care of the roll, but at the cost of blade meta!.
Click to expand...
Thanks for your input. I agree, definitely better rolling than chipping!
 
Jay2021 said:
Good point. Thanks for your input. This knife was sharpened very thin, so it was probably doomed to being rolled sooner than later. When I sharpen it again I'll consider putting a bigger angle on the edge.
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Another option would be to keep the factory angle and then put a steeper micro-bevel on it.
 
Over heating typically leads to a softening but not always. Certain steels have a secondary hardening around 1000 degrees F and grinding of thin sections can get there very fast. This steel is probably one of the ones that do this but the rolling indicates softening instead.

It not unheard of to get the very edge to hardening temperature in simple low alloy steels though we’re certainly not dealing with that here. In those cases the edge may just break away or possibly show improved performance for a short time though that would just be luck.

Power sharpening without coolant can readily overheat edges but that doesn’t mean they’re useless. Power sharpening can also give a higher sharpness than hand sharpening leading to a very sharp slightly softer edge that will perform well. Due to the uncertain nature of the overheating I’ve stopped power sharpening my blades at least until I can figure out a cooling system, which I’m not actually working on.
 
At this point: I'm sure hoping that this is the exception to the rule.
I just ordered another 20CV knife.
(Hogue Deka)
 
By the 4th or 5th sharpening it should be gone even if it is overheated. If not, avoid granite counter tops or similar surfaces and it should be ok.
 
me2 said:
Over heating typically leads to a softening but not always. Certain steels have a secondary hardening around 1000 degrees F and grinding of thin sections can get there very fast. This steel is probably one of the ones that do this but the rolling indicates softening instead.

It not unheard of to get the very edge to hardening temperature in simple low alloy steels though we’re certainly not dealing with that here. In those cases the edge may just break away or possibly show improved performance for a short time though that would just be luck.

Power sharpening without coolant can readily overheat edges but that doesn’t mean they’re useless. Power sharpening can also give a higher sharpness than hand sharpening leading to a very sharp slightly softer edge that will perform well. Due to the uncertain nature of the overheating I’ve stopped power sharpening my blades at least until I can figure out a cooling system, which I’m not actually working on.
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Thanks for your great input and sharing your expertise. Chances are this rolling is because of overheating/softening.
 
me2 said:
By the 4th or 5th sharpening it should be gone even if it is overheated. If not, avoid granite counter tops or similar surfaces and it should be ok.
Click to expand...
Thanks. I’m definitely avoiding granite countertops from now on!
 
Jay2021 said:
Interesting. Thanks for your input. Hopefully once the factory edge is sharpened off the tip will have better edge retention.
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To add to the Chronovore Chronovore quote, i think the difference is the speed of the factory belts. Im sure they take it under account but generaly, all sharpening devices we use at home are working in slower speds and this gives us some advantage. It is common practice among knife enthusiasts to re sharpen factory edges, usually right after purchase. I like to leave it for a while, it gives me chance to see if the factory angle suits my needs and to figure it out should l put steeper angle or not.
 
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