What the hell CPM 154?

ERIK KNIVES

ERIK KNIVES

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Aug 17, 2010
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I made a CPM 154 chef for my friend and it came out great. I was at his house tonight enjoying home made salsa among other things and he mentioned that it had taken on some rust. I looked at the knife and it had some hard rust spots on the surface in a few areas, the kind that would come off easily with a mild abrasive, but not my fingernail. More troublesome, was a small pit on the spine, toward the tip. He stores his knives in a wood block. He takes great care of his knives and wipes them down after use, no sink time, etc.

I have an AEB-L knife that I let my mother-in law and wife use - also stored in a wood block. I would say that this knife gets abused, whereas, my buddy's does not. It has no signs of rust what-so-ever and I am sure it has sat in moisture at one point or another. It is also super thin.

The CPM 154 holds it's finish better, and may be a point harder, but I don't want my kitchen knives pitting ever under reasonable conditions. Anyone have any thoughts here?

Erik
 
Several possibilities:
1) How was it heat treated? The rust proof abilities do not develop until after a full HT.
2) If the blade was finished on belts that were used with regular steel, it may impact tiny bits into the coarse grit grooves, and literally weld them in place. Later, they show up as tiny dots of rust and pits. I have been told that using a grinding magnet can cause this,too. Forged blades often get tiny pieces of scale and trash pounded into the bevels.
3) Bad steel?????? Who did the steel come from? While most claims of bad steel are excuses for our own problems, some steel is cleaner than others.
 
I was going to mention the HT. If you torched or clayed it, perhaps the alloying didn't get into full solution. I have never heard of Stacy's second possibility... makes sense other than the magnet part... still can't wrap my head around that one. Are you refering to bits of steel dust on the magnet being pushed into the grit grooves?
 
I have been using CPM 154 in the kitchen and I have never seen a spot of discoloration, maybe not CPM 154 A2?? I have worried about if I am really getting the steel that is ordered,
 
I have assorted knives in both CPM 154 and plain old 154 CM. I use one of them to open bags of salt for an industrial water softener and have never seen any discoloration even after failing to clean them for a couple of days. Something isn't right unless its from a belt sander like the second post said.
 
If using a magnet to hold the blades when grinding, it can cause other steel filings to become attached to the blade, and become burnished into the steel.. The blade itself may become magnetized, and attract tiny steel filings. When put in the foil and heat treated, these filings can burn into the blade and cause pits and rust spots later.
 
Rick Marchand said:
Okay... I've gone through the thread several times... Where the heck you comin' from, bro?
Click to expand...

I think he is referring to the secondary temper range of the higher alloy steels. Crucible sometimes recommends a higher temp range for some of their steels and some believe that it makes the steel slightly less corrosion resistant.

Is it possible that there are slight pits/scales left on the steel when finish grinding? Perhaps even a slight decarb from HT left over on the blade? The slight decarb discoloration sometimes blends in with the finish and is usually prone to rust if not completely removed.
 
Ah..... wow.... Okay, now it makes sense. You know, I have never considered tempering above 600F. For some reason, I remember Crucible saying that certain applications benefit from higher tempering heat but NOT recomending it, generally. I guess I was brainwashed into forgeting that bit.
 
My first thought was Stacy's second answer. When using belts that have ground carbon steel, you may end up sintering some of the carbon steel powder left in the grit of the belt to the stainless steel, creating scattered spots of rust and occasional pits. Out of curiosity, was the knife machine finished? I wonder if machine-finished blades have a higher incidents of this occurring vs. hand-sanded blades....

--nathan
 
Another possibility, who did the heat-treating. Some knifemakers heat treat their own steel, don't get it right and then blame the steel.
I have always felt better sending CPm 154, Ats-34, etc. to Paul Bos for heat treating. That way I know it's done right.
 
CPM-154 shouldn't do that. It's an excellent steel for the kitchen (and many other uses as well).

silver_pilate said:
I wonder if machine-finished blades have a higher incidents of this occurring vs. hand-sanded blades...
Click to expand...

I don't know, but it's a reasonable question. I would guess "yes", because almost everyone who hand-sands goes through a fair amount of clean paper after using any belts that may be dirty. I'm certain every belt in my shop is dirty to some degree, because even the brand-new ones just hang on the wall near the grinder. (come to think of it... that's not a very good idea... I should change that! :eek:)

Erik, to remove any "leftover" low-alloy steel that's stuck on, or ground into the blade, you may be able to get rid of it by re-sanding with fresh clean belts or paper. Then etch it. (I just use white vinegar on my 3V blades, never tried it on CPM-154 but it shouldn't matter.)

Look up "passivation" for more info. The etching technique is widely used in industry to address exactly this sort of problem. The idea is to remove stray grit and allow the free chrome to provide a thin, self-repairing corrosive-resistant layer on the surface of high-alloy steels.
 
Thanks for the replies folks, here is some additional information:

1.Trusted Supplier - AKS
2.Trusted HT - Peters
3.Clean belts, then clean paper on the disc, then clean paper for hand sand.
4.He mentioned when I first gave him the knife a few months ago, that the steel did show signs that it could rust, but it always wiped off. I never saw any rust on it when I was over until last night.

I pressed him a little more on his care/storage today. It seems that he washed with soap, rinsed, and let drip dry overnight on the sink/counter. The spine may have been in contact with his stainless sink where the pit occurred. The location and size of the rust spots would be consistent with final drops of water drying on the blade. It appears that I may have overstated his care, because I thought he always dried the knife by hand after washing. May just be a care issue. But, some of you seem to have done worse to the same steel without any problems. He hasn't had the issue with his commercial knives that have received the same treatment. Makes me wonder if James is on to something, I will look up passivation.

The other thing that perplexes me is that I am sure the AEB-L knife I mentioned gets crap care. I just went and pulled it out of the block, it was wet and put away slightly dirty. Par for the course. (not by me. I'm dealing with at least one person in my house that still can't break the habit of using a fork in a non-stick pan, so I don't need to hear what many of you are thinking.) That knife shows no sign of rust.

Thanks again, guys.
 
I don't have a definitive answer for you, but I'm very interested in what you find out regarding this particular knife. Please keep us posted!

I say again, that sort of pitting/rusting is not normal for a properly HT'ed blade in CPM-154. There's something weird going on. :confused:
 
I've got a knife in CPM 154 (custom by Stag & Steel), and I've left it covered in fingerprints for weeks at a time with no worries. When I come back to the knife, I just have to wipe it off with my shirt, and it's the same perfect mirror finish. I've never even gotten a tiny hint of rust forming on it. It sounds something's wrong with that knife...
 
I was talking to my buddy about my post. He's going to leave the knife as-is so I can take good pictures. Maybe I have unrealistic expectations, or maybe there is an issue. I will update you guys and once again, thank you.
 
Weird...I've put folders made of cpm154 through the washer and drier without knowing it an they showed zero discoloration....
 
I have made quite a few kitchen knives out of this steel and have not seen any rust or had anyone tell me that they have had any on their knives.
 
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