Fun with CPM-3V

james terrio

james terrio

Sharpest Knife in the Light Socket
Joined
Apr 15, 2010
Messages
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I made myself a new EDC a few weeks ago, in CPM-3V at 59Rc. To find out if/how badly this stuff really rusts, I left it with a very basic belt finish. It has not been etched or passivated at all. We've been using it daily in the kitchen for the last month, with strict instructions to NOT clean it after use, DO leave it lay around wet, etc.. Here's what happened:

SK3Vprotoabused.jpg


A bit rough, but not as bad as I thought. The orange spots could actually be mostly scraped off with my fingernail; a few passes on a clean A16 Trizact belt cleaned 'er right up. There is a tiny amount of tiny dark pits where some of the orange blossoming was.

SK3Vprotoreflection.jpg


All in all, I'm pretty pleased! For a steel with only 7.5% chromium, I expected a lot worse. I'm pretty sure that small of an amount is almost entirely tied up in carbides. I'll be carrying this one all summer with bare minimum cleaning and maintenance, to continue monitoring the corrosion-resistance and edge-holding (which so far has been outstanding).
SK3Vproto.jpg


Thanks for looking!
 
Have you had the chance to really test the edge retention of CPM 3V yet, I'm ordering some soon and so far am super excited to see how it performs. Did you do the HT, if so was it relatively simple or complicated?
 
Peters' did the HT. I will be doing the usual edge-retention tests as the summer progress; both shop tests and general in-the-woods goofing off. I have blades with almost the exact same geometry (as close to the same as I can grind 'em, anyway :D) in CTS-XHP, O1 and CPM-154 to compare it with.
 
3v is great steel i have made many neckers its gret hard use and since i have tested it in hottubs and pools its plenty rust resistant for me

i dont tho abuse them and leve then covered in crap all week
 
I carry a bead blasted 3v blade IWB every day, never seen a hint of rust on it. The only one I have had rust was one that I left in a wet sheath.
 
Yup, a wet sheath will do it every time, even with high-chromium steels.

I want to make it clear that I'm abusing this knife strictly for my own testing!* The point of this exercise is to give rust every chance, to see what happens in a worst-case scenario. Normally I take my blades to a much higher finish, keep them clean, and in some cases, passivate/blue/patina them. All of these steps make the most of any steel's corrosion-resistance.

*I don't think I'll purposely break this one, though. I like it too much :)
 
I wonder what B-B cuts in the hot tub ?

Jerry Hossom cuts things like steel pipe !!!
My chopper works fine on forsythia and other bush type things.
 
Actually, i think you can go even higher on the Rockwell than 59 with 3V. 61 probably isn't out of line. I love 3V.
 
your right danbo 61 is not a problem matter of fact im not sure what use i would even need to have it tempered down below that (its jsut that tuff)
 
mete said:
I wonder what B-B cuts in the hot tub ?

Jerry Hossom cuts things like steel pipe !!!
My chopper works fine on forsythia and other bush type things.
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jsut testing corrosion in hot bromine and pool chlorine
J and deker watched me take a mild steel can of caned Damascus billet with a 3v necker and ball peen hammer (had J diving for safty glasses adn cover behind the workbench as he was sure i was going to brake the 61RC knife )
 
If this one holds up like I think it will, I'll have the next batch done at 60 or 61 like you guys are saying. :thumbup:
 
James, what would you normally do to etch or passivate 3V?
 
Joe in the past I've just used plain white vinegar and let the blade soak overnight. The steel takes on a pleasant grey color with very little shine. FeCl would surely be quicker, and I think that's what most makers use, but I didn't have any on hand.
 
Thanks. I was wondering if you needed something stronger like muriatic acid. Does etching it increase the corrosion resistance substantially?
james terrio said:
Joe in the past I've just used plain white vinegar and let the blade soak overnight. The steel takes on a pleasant grey color with very little shine. FeCl would surely be quicker, and I think that's what most makers use, but I didn't have any on hand.
Click to expand...
 
jdm61 said:
Thanks. I was wondering if you needed something stronger like muriatic acid. Does etching it increase the corrosion resistance substantially?
Click to expand...

That's part of what I'm trying to find out. I'm sure etching helps in that regard, but I can't yet say how much. As I understand it, the main reason for passivating in that manner is to clean the finished part of tiny bits of steel, iron, grit etc that contribute to pitting. How well it improves overall corrosion-resistance would depend on the usual things like steel type, hardness, fineness of finish, etc. Passivating is a pretty interesting topic by itself and there's some good info on the web. Although not much of it relates directly to knifemakers, Jerry Hossom (a big proponent of 3V blades) has written about it and most of what I know comes from his threads. :thumbup:
 
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james terrio said:
For a steel with only 7.5% chromium, I expected a lot worse. I'm pretty sure that small of an amount is almost entirely tied up in carbides.
Click to expand...


Turns out, I was wrong about that.

3V only has about .8% carbon in it... that's enough to help it get good and hard (which includes forming ferric carbides) in HT, but there's not a whole lot of carbon left over to form other carbides.

3V has nearly 3% vanadium in it... that's where the name comes from. Vanadium in tiny amounts (1/2 % of total volume, or thereabouts) helps keep steel structures "tight" and "fine-grained" during HT... this is very good for toughness.

In larger amounts (2 or 3% and up) vanadium also forms small carbides very readily with whatever carbon is available. More readily than chrome does. < that's very important.

It also happens that vanadium carbides are much, much harder than plain steel or chromium carbides. Hence, better edge retention without sacrificing toughness.

So what happens to that 7 or 8% chrome in 3V? Nearly all of the carbon is tied up with iron and vanadium, so there's just not much carbon left for the chromium to bind with. It kinda just "floats" within the steel matrix and resists corrosion.
 
I like these kind of tests so thanks for posting James. Another reason I like to etch users is that, if you do happen to get a spot or two of rust on them is that you can rub off the surface rust with a dry rag, apply a little oil, & it blends in much better than it does on an un-etched blade.
 
I have a larger chopper from Survive knives in CPM-3V and HT'd by Peter's. I'm not sure of the hardness, but I have beat the living crap out of that knife and she still has a razor sharp edge.
 
stereo.pete said:
I have a larger chopper from Survive knives in CPM-3V and HT'd by Peter's. I'm not sure of the hardness, but I have beat the living crap out of that knife and she still has a razor sharp edge.
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I'm jealouse, I have wanted one of those survive choppers for a while now. From all the reviews I have read it sounds like CPM-3V is one of the best corrosion resistant carbon steel and it performs!!
 
stereo.pete said:
I have a larger chopper from Survive knives in CPM-3V and HT'd by Peter's. I'm not sure of the hardness, but I have beat the living crap out of that knife and she still has a razor sharp edge.
Click to expand...

I'm jealouse, I have wanted one of those survive choppers for a while now. From all the reviews I have read it sounds like CPM-3V is one of the best corrosion resistant carbon steel and it performs!!
 
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