How did ZDP189 go from a stainless steel to carbon steel?

[vivi]

If you read threads on this forum from five years ago, apparently everyone viewed ZDP189 as what it is - a stainless steel used on some Spyderco knives.

If you read threads from the past year, ZDP189 is now considered a carbon steel with no corrosion resistance.

Why has the perception of this stainless steel changed so much and what started this false rumor that ZDP189 is not a stainless steel?

Can anyone show me a ZDP189 knife with worse corrosion resistance than D2? Every single ZDP189 knife I've used has been magnitudes more corrosion resistant than D2, and in a completely sifferent dimension than stuff like O1, S7, 1095 etc.

Why is the corrosion resistance of these steels being equated, when they're so clearly on different levels?

[mrtodd777]

I have subjected my ZDP stretch to very corrosive environments that actually promote a patina (cleaning a deer-hot blood patinas carbon steels very quickly) and have not seen any corrosion whatsoever.

[vivi]

I have subjected my ZDP stretch to very corrosive environments that actually promote a patina (cleaning a deer-hot blood patinas carbon steels very quickly) and have not seen any corrosion whatsoever.

That's been my experience. I rust the majority of my knives to some degree, stainless or carbon, but ZDP189 has not been among them.

[fanglekai]

For the same reason that S30V went from premium to garbage steel that chips on everything. People repeat incorrect statements until it's the new normal.

[legOFwhat?]

I tried an acid etch on a zdp-manbug and kept the blade in the acid for well over an hour(10 minute intervals) and could only get a small tint change. I thought maybe the concentration was off so I threw in a cold steel aus-8 blade and a few minutes later the blade was a nice charcoal grey. ZDP is awesome!

[blues]

Maybe some folks wrongly came to the conclusion that it was laminated with 420 grade stainless steel because it was prone to corrosion when it was actually done to lend toughness. From there it's only a small step to erroneously deeming it a carbon steel.

Misinformation on the webz? Impossible!

[awa54]

By comparison to some of the ultra stain resistant steels it comes off second best, but none of my ZDP blades has suffered more than a hint of easily removed surface corrosion... Better than ATS-55 which pitted in my stainless scale D'fly.

I think corrosion resistance is a bit like edge retention now, expectations are so high that anything short of state of the art is considered poor performance...

[Rutger]

Too many bad stories about ZDP189 floating around the internet. People claim it rusts fast, hard to sharpen etc.

ZDP189 is pretty corrosion resistant. Since it is forming mainly chromium carbides in the steel it depends on the heat treatment how much chromium is left free in the solution. But based on Hitachi corrosion testing it is on par or better than 440C.
http://www.discipleofdesign.com/knives/ZDP189_eng.pdf

[Evil D]

Could be that expectations of what is good stain resistance have changed as we've started seeing steels that are far better at it than ZDP. Just in the time I've been on this forum there have been changes in a lot of standards and I've seen a lot of steels come into standard production that were once only obtainable through high end customs.


Thought I'd add, I used to carry a ZDP Ladybug on my keys, that was always clipped to my belt and tucked into my back pocket. That knife saw a lot of rain and body sweat and it did occasionally develop some spot rust (I'm pretty sure I have a thread here from years ago about it). Most of it would even wipe off but it does have some light pitting on the part of the blade that's exposed when closed.

[blues]

Carbon: 3.00%, Tungsten: 1.50%, Vanadium: .10%, Chromium: 20.00%, Molybdenum: 1.30%

[TomAiello]

In my experience it's very corrosion resistant.

The problem is the term "stainless" implies an all or nothing quality which is not accurate for the vast majority of blade materials. There needs to be a scale of "stainlessness" to really discuss this kind of thing.

[Bdubs808]

Very interesting thread. I started reading about super steels and ZDP189 less than 5 years ago; and from what I read about ZDP I came to the assumption that it was a carbon steel. And I was always confused because of the 20% chromium content. I have a Caly 3 with ZDP and I have always fretted about it getting it wet. The next time I carry it I'll worry a little less about keeping the blade oiled. Now it looks like a ZDP Delica or Endura is on my horizon...

[wrdwrght]

My ZDP189 (Stretch and Stretch2) has certainly been disinclined to develop a patina, but then it’s never been ridden hard and put away wet.

[JD Spydo]

Well VIVI I can inform you of one weakness that ZDP-189 is notorious for. If you do any food prep and/or food processing you better clean that bad boy as soon as you are done with it>> and I mean IMMEDIATELY!!! Because I learned the hard way twice with ZDP-189 that it does not have any resistance to many different food acids. First time was about 8 years ago when I had my vast tomato garden ( 21 varieties) and one evening I cut up one of my big Cherokee Purple tomatoes and I forgot to wash it off. The next morning it looked as though I had poured industrial strength acid on it and soaked it overnight .

On another occasion I used one of my ZDP-189 blades to help in cutting up a couple of deer during the season and it didn't take but about 4 hours and that blade had minor pits in it So with all that being said I personally can't regard ZDP-189 as a "stainless steel" because I can't see where it has hardly any better corrosion resistance than most high carbon blade steels have. I doubt if a 52100 blade would have done much worse to be honest about it >> I've sure never had my M390, XHP, S90V or any other stainless blade corrode that bad on me in such a short period of time. And this is coming from a guy who is still a fan of ZDP-189>> but I've learned the hard way that it doesn't have many of the desirable properties that most stainless blade steels do.

[ferider]

I have subjected my ZDP stretch to very corrosive environments that actually promote a patina (cleaning a deer-hot blood patinas carbon steels very quickly) and have not seen any corrosion whatsoever.

Same here. It's a great kitchen knife. For me, ZDP is stainless.

[SpyderEdgeForever]

Vivi, I was originally going to get a Spyderco ZDP Endura, and after exclusively reading threads on this forum, I was convinced that it is a very rustable steel, like 1095 carbon steel. I wish I had discussed this with you right away, my friend. I consider you, Surf Gringo, JD Spydo, and The Peacent, to be four of the best "Corrosion Resistant Knife Experts" on the forum, along with sal, ofcourse. One of my personal biggest fears when it comes to knives and corrosion, is for a knife blade to become pitted or lose integrity due to corrosion.

And so here is my question to the four of you: Do you think it is most likely better for me to stick with a steel that is definitely safe from rust, ie, H1, Lc200N, VG10, and AUS 8A, or, would it be worth it to try ZDP 189?

[SpyderEdgeForever]

I have subjected my ZDP stretch to very corrosive environments that actually promote a patina (cleaning a deer-hot blood patinas carbon steels very quickly) and have not seen any corrosion whatsoever.

Same here. It's a great kitchen knife. For me, ZDP is stainless.

I am a bit confused. How is this possible? My scientific mind says that like things are like and opposite things are opposite. If a steel blade is placed in one enviroment, and if that same blade is placed in an identical enviroment, then identical results should come about.

[ejames13]

Does anyone have a copy of the "Thanx Much" letter that comes with ZDP knives? I thought I remembered it saying ZDP was either not stainless or was semi-stainless.

I've had it develop speckled rust from wearing inside the waistband, which has never happened to me with my VG-10 knives.

[supracor]

Carbon: 3.00%, Tungsten: 1.50%, Vanadium: .10%, Chromium: 20.00%, Molybdenum: 1.30%

Obviously you don't know how much carbides can create 3%C.

I repeat that another time.

Zdp189 with the proper temper have all the Chromium in Chromium carbides; moreover it contains CR23C6 carbides, like all the steels that contains more than 12% Cr. CR23C6 is weaker than CR7C3 and eat a lot more Chromium but it's still a carbide and therefore harder than martensite.

http://webmineral.com/data/Tongbaite.shtml#.W7execvOM0M

Now do whatever you want; it will not change a fact.

[TomAiello]

It sounds like you're saying that the stain resistance of ZDP is just like the stain resistance of almost any knife steel--it depends on the heat treat. Is that right?