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

[supracor]

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?

This and obviously the Chromium content.

There are many high-hardness high wear-resistant Chromium-Vanadium steel nowadays, and many are designed specifically to have a relatively high corrosion resistance (20CV, S90V, S110V, S125V, etc ...), but as it is well known they have a strict HT which leads to a high HRC but certainly not to the maximum attainable.

This is not the case of Zdp189.
Zdp189 is created to have a superhigh hardness (i've seen it at 69 HRc), a S90V-class wear resistance and still maintaining an ease of sharpening way higher than S90V.
How it achieve this wear resistance? By Chromium carbides, that is the only motive why Chromium is here.
Mr. Kitano, the developer never cared of corrosion resistance, he wanted ease of sharpening and superhigh hardness/wear resistance.

This is the same motive why D2 has 12% Cr.

[Rutger]

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?

Yes.

ZDP189 at high hardness will have used more of the chromium to form carbides. Same with other steels like M390 etc. Except ZDP189 only has chromium to consume whereas other steels also got vanadium and other elements to form carbides. The final corrosion resistance of any steel depends on the heat treatment. You could probably heat treat M390 to such a hardness that it is much more rust prone. So when one guy has a ZDP189 knife with rust issues it doesn't mean all ZDP189 will behave the same way cause of different heat treatment.

440C which ZDP189 is similar to in corrosion resistance is with normal heat treatment at around 12% free chromium in solution. So i guess we can assume ZDP189 is around that level too (not the 20% it starts with). Something is considered a stainless steel when above ~11% Cr. But maybe when they run ZDP189 very hard it will drop below 11% Cr. And even steels with 11-12%Cr can corrode, that's why it is called stainless.

Larrin from Knifesteelnerds had a great article about this concept for D2 steel.
https://knifesteelnerds.com/2018/06/11/ ... stainless/

[vivi]

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.

If it makes you feel better, I've done that to VG10, BD1, AUS8 and S30V :)

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?

It depends on your priorities.

For my uses, nothing has held an edge longer than PE ZDP189 when it comes to small folders. It is also surprisingly easy to sharpen for how pong it holds an edge. I noticed the corrosion resistance is a little worse than VG10, roughly on par with my 8Cr13MoV Byrd knives. That's good enough for most folks.

[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.

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.

I'm sure this is true, but also that we all have a different environment. So here is "Roland's stainless test :)":

In the evening, I cook (use the Stretch for veggie and fruit cutting, and use a Police 4 to cut meet); knives are dirty for maybe an hour or two. All this in a dry Californian kitchen. Then I wash up (no towels), and let the knives dry overnight, open. Next morning, I look at the two knives: the P4 is pitted, the ZDP Stretch is sparkling clean.

Cheers,

Roland.

[vivi]

oops, double post.

[ZMW]

I bought my ZDP stretch second hand. What a great knife and steel. I have had no chipping issues (everyone complains how chippy it is too). I have not beaten it up too bad, but it has gone through metal staples and other tough materials

The blade came with a slight patina or light staining over certain areas of the blade. I am not sure what i was put through before, but it is has been a stainless knife for me. But, I treat it a little more gently then my vg10 or other stainless knifes when it comes to drying it off.

Great knife, bang for the buck one of the best on the market

[ZMW]

Here is a pick, not sure what caused this very specific patina. And only on one side of the blade.

[Evil D]

Here is a pick, not sure what caused this very specific patina. And only on one side of the blade.

Will that polish off or is it a deeper stain?

[ZMW]

Here is a pick, not sure what caused this very specific patina. And only on one side of the blade.

Will that polish off or is it a deeper stain?

I have hit it with flitz a couple times and nothing, but that’s all I have tried. I don’t mind it, so no big deal.

The pic

[ZMW]

As I look at my knife now, the grey patina is a little exaggerated in that pic. But, it’s still noticeable.

[ZrowsN1s]

I've seen ZDP get a few specks of rust. But my buddy who carries ZDP exclusively is the kind of guy who doesn't do much knife maintenance, he'll cut food with it and give it a paper towel wipe off and put it back in his pocket (if he wipes it off at all). With absolute minimal (to no) maintenance even after 2 years his knives look pretty good. They look used, but not rusted, and not patina'd like a tool steel would be.

[Evil D]

As I look at my knife now, the grey patina is a little exaggerated in that pic. But, it’s still noticeable.

What really is the difference between a patina and a stain? I think of a patina as a layer that forms on the surface, while a stain is deeper embedded into the steel which is why it won't easily polish off. I may be completely wrong, that's just how it seems in my mind. I had a similar issue with S30V and my first Paramilitary, it had a price sticker on the blade for who knows how long and the glue stained a rectangle into the steel that never went away.

[Jazz]

I really like the look that ZDP gets after a while. Just dark and “steely”. :cool:

[harronek]

I would really like to know if there is a difference between the ZDP used on Caly 3 and 3.5 knives and the Delica - Endura line ?
I have an old Caly 3.5 that I bought secondhand and it arrived with a slight patina to the ZDP .
Over a period of time the patina escalated to a heavy patina which helped me make the decision to alter and customise the knife ( it wasn’t pristine anymore )
I have a Delica ZDP that has never really changed much and has been exposed to a heavier workload and hard life .
Does the clading process of the Caly blade change the ZDP properties somehow ?



Ken

[zhyla]

Interesting discussion. I guess you could say that ZDP-189 started out with the reputation of a stainless steel but over time it tarnished :)

I'll show myself out...

[The Deacon]

Can't speak for anyone else, but I've considered it semi-stainless for over ten years. Ever since the first rust spots appeared on the CF Stretch I'd been carrying for less than a month.

[Daveho]

Interesting discussion. I guess you could say that ZDP-189 started out with the reputation of a stainless steel but over time it tarnished :)

I'll show myself out...

Well done sir :)
*clap* *clap*

[Daveho]

I've seen ZDP get a few specks of rust. But my buddy who carries ZDP exclusively is the kind of guy who doesn't do much knife maintenance, he'll cut food with it and give it a paper towel wipe off and put it back in his pocket (if he wipes it off at all). With absolute minimal (to no) maintenance even after 2 years his knives look pretty good. They look used, but not rusted, and not patina'd like a tool steel would be.

He’s like me and here’s a tip when using knives for lunch time food prep you can give your knife a sneaky wipe on your sock to remove the yuck
Perfect

[JimP]

Does the clading process of the Caly blade change the ZDP properties somehow ?

Ken

That's an interesting question! Like galvanic corrosion and the ZDP acts as a sacrificial steel. Would be very interested in hearing from someone that is knowledgeable about such things.

[SpyderEdgeForever]

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.

Tom, I have been desiring just such a measurement scale for some time. Thank you for posting this! Some form of scientifically accurate and objective chart that can be regularly updated with the introduction of new blade steel alloys; that show a scale of stainlessness, perhaps starting with your very basic core carbon steel such as 1055 and 1095 and others, and then going on to such alloys as 440 series, AUS series, and peaking with the nitrogen alloys such as H1 and Lc200N, and N690, that sort of thing. This would be very helpful with knife selection.