Normal 20CV behavior?

F

ForgedMaple

Joined
Jan 11, 2017
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Hey guys, looking for some help and feedback here from people who have experience with CPM 20CV steel, particularly on Bark River knives.

Last Sunday I acquired my first BRKT piece; a mini-canadian in 20CV. I use my EDC blades for mostly light use, but I do enjoy doing some food prep here and there. So yesterday, I was having breakfast and decided to slice up a banana. I was a bit shocked, as immediately after cutting, I washed the blade with soap and saw dark streaks near the edge, typical of what I'd normally see on my 1095 stuff (it's a bit hard to catch on camera, so I'm putting up larger pictures)

2n0owfs.jpg



I figured perhaps bananas are a lot more corrosive than I previously thought and shrugged it off. This morning, however, I started thinking about how 20CV is claimed to be exceeded only by stuff like H1 when it comes to corrosion resistance, and how I've never, ever had any problems with any other stainless, be it in a folding or kitchen knife. So I decided to put the Barkie to the test again and sliced up an apple (an ambrosia, for those wondering). This is how it looked afterwards:

zjv3ao.jpg



As you can see, the forward half of the blade is clearly stained, with obvious blotches near the tip. So my question is, is this to be expected on 20CV? Again, I've never seen such discoloration on anything but basic carbon steels. Even 4V took MUCH longer to stain in kitchen use.

I normally don't make a big fuss of stains (I actually like patina), but I paid a clear premium on this knife expressly for the purpose of better corrosion resistance than A2, and right now I'm not really seeing it.

Anybody with similar experiences? Thank you for reading :)
 
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You know, maybe it's the camera angle, but I'm having a hard time seeing the banana marks after you sliced your apple. Could just be the camera angle/lighting, but do they appear gone now?

Also just as a curiosity question, what kind of soap did you use to wash these off and was it the same soap both times?
 
Amoo, the "banana marks" are still visible, they just seem to show off at a different angle than the "apple stains" so I can't capture both simultaneously. The discoloration is still quite faint to be honest, but I've just never seen something appear this fast with so little use on stainless stuff.

The soap is just regular dishwashing soap that I use on all my knives. Same soap both times.

Now I'm not assuming 20CV is bomb-proof in the corrosion resistance department just from the 20% Chromium (see ZDP-189), but most of what I've read seems to point to it being pretty damn good at staying shiny. The reason I'm raising the question here is that I found 20CV info to be somewhat scarce, with a lot of the feedback coming from M390 and being extrapolated to the former.
 
Banana stain is similar to dye(not oxidation) can easily remove with bar-keeper-friend/bleach/acetone.
 
Luong,

I recalled cutting banana with BCMW 52100 and immediately the stain is black. :eek:
Sorry for OT, but interested to understand since you mentioned like dye.
 
I don't have a banana handy, but I soaked my Adventurer2 in vinegar for five minutes, and couldn't see any staining at all. Any shade in the picture below is just reflection.

32226693266_ed40a81b4a_b.jpg
 
My grip in 20cv has a slight patina after some use. It doesn't show up in pics but in person you can tell, but only if you know what it looked like new if that makes sense. It has taken a slight and even patina much like my Cruwear Manix 2. This surprised me as I thought it was supposed to be very stainless. It doesn't bother me at all, but certainly not what I was expecting.
 
Banana sap (dull grey dye :)) is very persistence on any surface with open pores/groves/grind-line. I cut a stem of banana a few times and let it dry with my very rough grounded 20cv paring knife. Under 400x metallurgical microscope - saw nothing (no sign of rust nor pitting). Using atom count formula - I simulated scenario for below avg ht - free Cr is still above 13%, so corrosion resistant is above guide/label line consider as stainless (yeah, mean only trivial oxidation beyond Cr passivation layer).
 
I just stained a ceramic blade (with visible grind lines) with banana sap. It takes more than detergent to remove this stain - i.e. liquid hi/low Ph or solvent to dissolve this stain (and other stains/dyes in general). btw - elephant ear plant sap is a bluish turbo version of banana.

Chris "Anagarika";16820836 said:
Luong,

I recalled cutting banana with BCMW 52100 and immediately the stain is black. :eek:
Sorry for OT, but interested to understand since you mentioned like dye.
Click to expand...
 
Looks to me like the banana sap highlighted the scratches in the blade that are deeper than the satin finish. If you didnt put them there, then it is bark river's fault. They should have properly applied your satin finish so there werent grooves in it from the previous operations.
 
I think this is normal. I saw the same reaction with my XHP knives, when i forgot to wipe it off after cutting banana. It left purple-ish patina on the blade, probably from reacting with other elements in the steel.
 
If that is an actual stain (I will take your word for it!) then that is absolutely not normal for 20CV.

20CV has a fairly high Chromium content, and I have used it a lot.
It is a highly "stainless" steel.

You should put a few drops of lemon or vinegar on the blade, leave it for 5 minutes, then wash with soap.
See what happens.

If it leaves a Patina then there is an issue in terms of what the corrosion resistance of that steel should be...
 
Thank you for all the feedback guys, I appreciate it.

Andre, the knife cut nothing more than some tape and paper before getting to the banana, so if there are any scratches on the blade, I can guarantee they were already there. To be honest, the overall F&F is nothing to write home about, with asymmetrical plunge lines, uneven scales, small but deep scratches on the spine, etc. I understand Bark River still does a lot of the work by hand, so I figure it's normal. I wasn't expecting CRK-style tolerances.

JR88, I tried leaving the blade in some apple cider vinegar for a minute or two after seeing Dangerously's post. It may or may not have slightly darkened the blade. I'll give it the benefit of the doubt for now and try putting it in white vinegar for 5-10 mins when I get home later. I'll update if there's any significant changes to the finish.

Again, the stains are faint and only visible in certain lighting conditions. I really like the design of this knife and will keep on carrying and using it, but I just hope I won't have to start worrying about actual rust or pitting. I bought this knife kind of hoping for a change of pace from all of my GEC stuff :o

As for contacting BRKT, I don't feel the issue is with the manufacturer (unless it's related to heat treat?), I just wanted to hear people's experience with this specific steel. I find it a bit confusing, as it seems Duratech 20CV used to be made by Latrobe, which has been acquired by Carpenter, which apparently discontinued it in favor of 204p, so I'm not sure where the CPM version fits in all of this.
 
Crucible bought the formula from the Latrobe before Carpenter bought Latrobe, but that has nothing to do with what you are experiencing.

Just because a steel has a high amount of chromium doesn't directly translate to how stainless the blade is, it's the relationship between how much carbon and chromium is in the blade and what heat treatment that determines that, example, ZDP-189 also has 20% chromium but is not very stainless because a lot of that chromium is tied up with the 3% carbon to make it very "wear resistant" which means that there is not as much as one would think of "free chromium" for the passivization of rust. its the same reason on the opposite end that steels like h1 and 420j2 (very low carbon) make good dive/water knives especially h1"rust proof" but they wont touch the wear resistance of even a budget steel like chinese 8cr13mov and higher

also if you look at the spec sheet for heat treating cpm 20cv

https://www.alphaknifesupply.com/Pictures/Info/Steel/20CV-DS.pdf

you see the different temperatures ranges recommend by the steel mill, they show you that you have to make compromise between wear resistance and corrosion resistance. its not that cpm 20cv is special in this regard, all steels have these compromise that must be made with heat treating.
So maybe Bark River chose more wear resistance, who knows, if it bothers you just give them a call or choose a more balanced steel to meet your expectations.

Of course its always a compromise to have it all, just keep that in mind.

you cant have everything so choose what you like to enhance what you place the most emphasis on.


I am a steel nerd but honestly, with knives its geometry and heat treat that is the most important, steel is the always the biggest focus but its just the ingredients which only gets the performance from the right mix of geometry and heat treat.

but they don't have names for geometry ( thickness from spine to edge , not type of grind) and heat treatment( its more complex then just what HRC)
those are more complex to understand then what steel type.

So the steel name is the most identifiable feature for guys buying knives that haven't played with a few to see what works for them with how they are use them for certain tasks and what preferences are the most valued.



either way, just enjoy that knife.

cpm 20cv is awesome stuff.

cheeers
 
DeadboxHero said:
Crucible bought the formula from the Latrobe before Carpenter bought Latrobe, but that has nothing to do with what you are experiencing.

Just because a steel has a high amount of chromium doesn't directly translate to how stainless the blade is, it's the relationship between how much carbon and chromium is in the blade and what heat treatment that determines that, example, ZDP-189 also has 20% chromium but is not very stainless because a lot of that chromium is tied up with the 3% carbon to make it very "wear resistant" which means that there is not as much as one would think of "free chromium" for the passivization of rust. its the same reason on the opposite end that steels like h1 and 420j2 (very low carbon) make good dive/water knives especially h1"rust proof" but they wont touch the wear resistance of even a budget steel like chinese 8cr13mov and higher

also if you look at the spec sheet for heat treating cpm 20cv

https://www.alphaknifesupply.com/Pictures/Info/Steel/20CV-DS.pdf

you see the different temperatures ranges recommend by the steel mill, they show you that you have to make compromise between wear resistance and corrosion resistance. its not that cpm 20cv is special in this regard, all steels have these compromise that must be made with heat treating.
So maybe Bark River chose more wear resistance, who knows, if it bothers you just give them a call or choose a more balanced steel to meet your expectations.

Of course its always a compromise to have it all, just keep that in mind.

you cant have everything so choose what you like to enhance what you place the most emphasis on.


I am a steel nerd but honestly, with knives its geometry and heat treat that is the most important, steel is the always the biggest focus but its just the ingredients which only gets the performance from the right mix of geometry and heat treat.

but they don't have names for geometry ( thickness from spine to edge , not type of grind) and heat treatment( its more complex then just what HRC)
those are more complex to understand then what steel type.

So the steel name is the most identifiable feature for guys buying knives that haven't played with a few to see what works for them with how they are use them for certain tasks and what preferences are the most valued.



either way, just enjoy that knife.

cpm 20cv is awesome stuff.

cheeers
Click to expand...

Thats a great explanation, Thank you
 
DeadboxHero said:
Thanks brotha :)
Click to expand...

Hey Deadbox, thanks for taking the time to write a reply in so much detail, that's a lot of good info in a single post. I also had no idea that heat treatment protocols were easily accessible online, so thanks for sharing that as well.

So I guess this is all pretty normal stuff. I'll certainly be enjoying this knife, patina or no patina. It's a sweet design.
 
Do a Good, Bad &Ugly search on Bark River and its owner. I wouldn't be suprised by anything. I belive the Micocanadian has been made in many steels.
 
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