CPM-M4 vs CTS-20CP/CPM-S90V

[CrimsonTideShooter]

Like spydusse and Ken44 said, it's technically considered a stainless steel since that designation is based purely on the chromium content. There are various numbers floating around for what, exactly, the required chromium percentage is, but since all are in the neighborhood of 12-13%, ZDP's 20% easily exceeds the threshold regardless of which particular standard one uses.

However, I do agree with your underlying point that, even though it meets the technical, chromium-percentage-based standard for "stainlessness", ZDP is very susceptible to rust/patina formation. Even if corrosion resistance were a major concern for me, there are a lot of technically non-stainless steels that I'd take in a heartbeat over ZDP for that purpose (e.g., 3V, M4, INFI, D2, etc.).

Exactly. Thanks for explaining it.

 

[Ankerson]

ZDP isn't stainless. Sure it has 20% chromium, but it is all tied up forming carbides.

I wouldn't say it's all tied up forming carbides, but likely around 8% or 9% maybe then taking into count the very high hardness it is usually run at (65-66 HRC) we lose some stain resistance due to the chemical changes in getting it that high.

With steels to get some things we must give up other things to get them, no free lunches with steels.

 

[Sal Glesser]

Actually ZDP is a stainless steel. It is less stain resistant than some, but , when compared to something like O1, much better. There is enough chrome to create an oxide barrier. Better than D2, not as good a AUS-8.

sal

 

[cziv]

Thanks for your input Sal!

 

[knarfeng]

I know that, anything above 13% is "considered" stainless.


Doesn't mean that it IS stainless.

Yes it does. It stains less than carbon steel.

It didn't say how much less it stains. Just that it stains less.

You may think I'm being a smart alec (and to a certain extent you would be correct), but in truth there is no real performance parameter associated with the term "stainless". It just means that it does not corrode as much, not that it does not corrode at all.

 

[knarfeng]

I've always been amused by the German term "Rostfrei", or rust free, vs. the English term "Stainless", or stains less. Germans are known for precision, but in this case the English/American idiom is more precise.

aerospace materials engineers call it "CRES" = Corrosion REistant Steel. There is a definite understanding that it "resists corrosion" and is not "corrosion proof".

 

[cziv]

I've always been amused by the German term "Rostfrei", or rust free, vs. the English term "Stainless", or stains less. Germans are known for precision, but in this case the English/American idiom is more precise.

aerospace materials engineers call it "CRES" = Corrosion REistant Steel. There is a definite understanding that it "resists corrosion" and is not "corrosion proof".

Leave it to NASA to get it right!

 

[CrimsonTideShooter]

Yes it does. It stains less than carbon steel.

It didn't say how much less it stains. Just that it stains less.

You may think I'm being a smart alec (and to a certain extent you would be correct), but in truth there is no real performance parameter associated with the term "stainless". It just means that it does not corrode as much, not that it does not corrode at all.

Smart alec! I won't tolerate this tom foolery!



Haha j/k, thanks for the education.

 

[db]

You want tom foolery? Ok then. I'm going to disagree with Sal. In my limited experience with ZDP it does corrode easier than D2. Now, hows that? Disagreeing with one of the most respected people in the cutlery biz with a hole lot of knowledge, and probably has tested both steels on this very subject. And then there is me just a goof on the net that just has 1 ZDP knife, and a couple of knives in D2.

 

[spydusse]

You want tom foolery? Ok then. I'm going to disagree with Sal. In my limited experience with ZDP it does corrode easier than D2. Now, hows that? Disagreeing with one of the most respected people in the cutlery biz with a hole lot of knowledge, and probably has tested both steels on this very subject. And then there is me just a goof on the net that just has 1 ZDP knife, and a couple of knives in D2.

have you treated one or the other with oil or flitz,were you maybe subconsciously more cautious with your d2 because it doesn't have the title stainless?I wouldn't know because I only own one blade in cpmd2 that I bought over the winter so when it was time to go back to work at the nursery in the spring it had already lost its flavor of the month title to a few other more recent purchases.I've only carried it a hand full of times this past year, it didn't hold and edge as long as my xhp but it cuts very similar. I guess that's why they call xhp a stainless d2

 

[db]

No to both questions. I pretty much never oil or treat my knives for corrosion as I'm just not concerened about them rusting at all.

 

[CrimsonTideShooter]

have you treated one or the other with oil or flitz,were you maybe subconsciously more cautious with your d2 because it doesn't have the title stainless?I wouldn't know because I only own one blade in cpmd2 that I bought over the winter so when it was time to go back to work at the nursery in the spring it had already lost its flavor of the month title to a few other more recent purchases.I've only carried it a hand full of times this past year, it didn't hold and edge as long as my xhp but it cuts very similar. I guess that's why they call xhp a stainless d2

D2 is close enough to the threshold of stainless that it pretty much IS stainless. It's not the rust monster that people make it out to be. It's literally 1 % away form making the "satinless club."

And as it was pointed out here, no one actually knows the TRUE threshold for stainlessness. So, I (ME, alone!! My opinion!!) consider D2 a stainless steel, and I treat it as such. Never had any problems. And I live in a VERY humid environment.

 

[sodak]

Oh, I'm always learning from my knives and edges. Somedays I learn I prefer a coarse edge and then there are the other days I learn I prefer a polished edge. Truth is my needs do change depending on what I'm doing and I really notice what type of an edge is needed moreso than any difference between most of the better steel types. I'm kind of a retired steel snob. I've tried many different steels and really haven't been blown away by any of them for very long. Like most here already know you give up one thing to gain in another and for a edc knife what ever is lacking in the steel is going to show up sooner or later.

I'm pretty much with you here db, I'm interested in learning, and love to read these threads. The sad fact of the matter is that my needs aren't that great unless I'm working in the yard, on the farm, or I'm in the woods. But since I work in an office, well, my interest is more academic than anything. I still appreciate the super steels, and enjoy using them, but I also enjoy other ones as well. All things being equal, I'm gravitating towards using a steel in some of Ankerson's tiers that are easy to sharpen - I'm getting lazy! Of course, ease of sharpening is as much a function of geometry as steel and heat treat.

I got into knives years ago thinking it would be cheaper than guns, and you could learn everything about them in a relatively short time - just a hunk of steel. Wrong and wrong.

 

[Ankerson]

I'm pretty much with you here db, I'm interested in learning, and love to read these threads. The sad fact of the matter is that my needs aren't that great unless I'm working in the yard, on the farm, or I'm in the woods. But since I work in an office, well, my interest is more academic than anything. I still appreciate the super steels, and enjoy using them, but I also enjoy other ones as well. All things being equal, I'm gravitating towards using a steel in some of Ankerson's tiers that are easy to sharpen - I'm getting lazy! Of course, ease of sharpening is as much a function of geometry as steel and heat treat.

I got into knives years ago thinking it would be cheaper than guns, and you could learn everything about them in a relatively short time - just a hunk of steel. Wrong and wrong.

AUS-8 is a great user steel if it's done right and it's very easy to sharpen, it's also fine grained so it will take a wicked sharp edge.

My garage knife (Beater knife) is in AUS-8, I just hit it with a ceramic rod every now and then and in seconds it's VERY sharp again.

 

[Sal Glesser]

Hi Db,

I've not tested them side by side (D2 & ZDP). I carry ZDP quite a bit, but D2 less, so my comparison was more of a guess from my own experience. Have you had much corrosion on your ZDP & which model do you have?

sal

 

[Neo]

I've always been amused by the German term "Rostfrei", or rust free, vs. the English term "Stainless", or stains less. Germans are known for precision, but in this case the English/American idiom is more precise.

aerospace materials engineers call it "CRES" = Corrosion REistant Steel. There is a definite understanding that it "resists corrosion" and is not "corrosion proof".

And the French call it inox (from inoxydable)

 

[cziv]

And the French call it inox (from inoxydable)

Ah hah! That's why my little Beretta 21A .22 pistol is called the 21A INOX model because it has a satin finish ss slide! Thanks.

 

[rustyrazor]

this forum has gotten soooo far off the rails, lol. what happened to the performance of the blades... we all know nobody cares what the french call anything "freedom fries" anyone??

 

[db]

No Sal, I haven't had much corrosion on my ZDP. The knife I have isn't one of yours. I haven't done a side by side either. It is just my opinion based on general carrying and use. Truth is I've carried my D2 knives alot more than the ZDP and haven't had any corrosion issues with D2 at all. With the ZDP I'd say it was very minor just alittle spotting not really anything that concerned me. I just remember being a little surprised by it. I haven't had or use the ZDP in about a year. However, I do think that the finish on both the ZDP and the D2 knives were pretty close to the same as I put on a very shallow convex edge on all my knives. At the time I did sharpen everything the same way and to the same finish. At that time my finished edge was the Spyderco white ceramic bench hone. Yes I do convex with bench hones, it is easier to do than people think.

 

[hardheart]

corrosion resistance is also affected by heat treat, not just alloying. How much chromium gets tied up is affected by austenizing and tempering temperatures. If a stainless blade is given a high temper for a secondary hardening response for more wear resistance, it loses some corrosion resistance.