ZDP-189 and Cowry-X: Overrated or Super Steel?

Lodd said:
This isn't the first time I've been annoyed by all the marketing around steels, especially the so called 'super-steels' and how liberal they can be with the truth, but selling carbon steel as stainless steel really takes the cake.

I've read the article, but I can't say I understand all the nitty-gritty details. In practice, how would this compare to D2 in terms of corrosion resistance?
Click to expand...
https://knifesteelnerds.com/2019/10/14/corrosion-resistance-testing/
 
Lodd said:
This isn't the first time I've been annoyed by all the marketing around steels, especially the so called 'super-steels' and how liberal they can be with the truth, but selling carbon steel as stainless steel really takes the cake.

I've read the article, but I can't say I understand all the nitty-gritty details. In practice, how would this compare to D2 in terms of corrosion resistance?
Click to expand...
.

The exposed ZDP on my William Henry Blade is a lot more stainless than D2.
 
I don't have any chipping issues with Spyderco ZDP. I also do nothing to the blade to prevent corrosion (besides maybe a wipe of oil every once in a while, usually after I've oiled the pivot) and have been perfectly fine.
 
I appreciate all the people providing feedback; both positive and negative examples of this steel, it helps make a point:
that zdp189, given a decent heat treatment (likely around 59-60 hrc, which is quite low for it's range), can perform well

The lower hardness likely helps both toughness and rust resistance, which are usually pain points for this steel.
My gut feeling is it's still not an optimal choice... it's like putting a speed limiter on a high end sports car to deal with traffic tickets

(older zdp delica's were supposed to be around 64 ... but I honestly don't know if that's still the case)
 
Last edited:
My ZDP at 67HRC does not have chipping or rust issues. This is based on 20 years of actual use rather than gut feelings. I have a plethora of high end knives with premium blades, and I lean toward ZDP because it is optimal in my experience.
 
tiguy7 said:
My ZDP at 67HRC does not have chipping or rust issues. This is based on 20 years of actual use rather than gut feelings. I have a plethora of high end knives with premium blades, and I lean toward ZDP because it is optimal in my experience.
Click to expand...

Must be the unicorn blood that W/H uses to quench their San Mai blades in. It imparts 420j2 stain resistance and toughness to ZDP core, while the core stays hard and wear resistant.

On a slightly more serious note, have you tested the hardness of your core? Just because a maker says the blade is of a certain hardness, doesn't mean it is. You are clearly seeing and experiencing what you say, but you have to agree that this is a very bizarre behavior to see very stainless clading rust and a semistainless steel not. The clading had to be screwed up pretty badly for 420j2 to rust, it has very high stain resistance usually.
 
dirc said:
I appreciate all the people providing feedback; both positive and negative examples of this steel, it helps make a point:
that zdp189, given a decent heat treatment (likely around 59-60 hrc, which is quite low for it's range), can perform well

The lower hardness likely helps both toughness and rust resistance, which are usually pain points for this steel.
My gut feeling is it's still not an optimal choice... it's like putting a speed limiter on a high end sports car to deal with traffic tickets

(older zdp delica's were supposed to be around 64 ... but I honestly don't know if that's still the case)
Click to expand...
ZDP-189 doesn't really go down to 59-60 Rc unless using extreme heat treatments. And with high carbide steels they tend to not see much improvement in toughness when reducing hardness. See the following diagram as an example:
toughness-vs-hardness.jpg

Going lower in hardness would also not help its corrosion resistance. It would require "underaustenitizing" which would reduce corrosion resistance.
 
ace said:
Must be the unicorn blood that W/H uses to quench their San Mai blades in. It imparts 420j2 stain resistance and toughness to ZDP core, while the core stays hard and wear resistant.

On a slightly more serious note, have you tested the hardness of your core? Just because a maker says the blade is of a certain hardness, doesn't mean it is. You are clearly seeing and experiencing what you say, but you have to agree that this is a very bizarre behavior to see very stainless clading rust and a semistainless steel not. The clading had to be screwed up pretty badly for 420j2 to rust, it has very high stain resistance usually.
Click to expand...

The stainless cladding may not be for rust. In the early years of ZDP, it was stated by some companies it was to lower the cost of the blade and increase the blade's (not edge) toughness.

I get William Henry e-mails, and the one for today features a knife with a blade made from "William Henry's patent pending Wave Damascus features a ZDP-189 core (HRC 67) clad with alternating layers of stainless steel and nickel silver. The billet, 45 layers in all, is patterned with a custom die to create the undulating waves that emerge across the bevels of the blade. This material can be dark-etched for contrast, or etched and re-polished for a more subtle pattern." They have claimed a ZDP hardness of about 67 for at least 15 years and based upon performance of my knife, I'd say it's greater than every steel in my stable, hardest being O1, L6 and M390 at 60-62.
 
ace said:
Must be the unicorn blood that W/H uses to quench their San Mai blades in. It imparts 420j2 stain resistance and toughness to ZDP core, while the core stays hard and wear resistant.

On a slightly more serious note, have you tested the hardness of your core? Just because a maker says the blade is of a certain hardness, doesn't mean it is. You are clearly seeing and experiencing what you say, but you have to agree that this is a very bizarre behavior to see very stainless clading rust and a semistainless steel not. The clading had to be screwed up pretty badly for 420j2 to rust, it has very high stain resistance usually.
Click to expand...
I haven’t tested the ZDP for hardness, but given the edge holding, I don’t suspect that it is lower than advertised. I have experienced some spotting (surface rust) on both the 420 and the ZDP, but it was surprising that there was more spotting on the 420 than the ZDP. There was no pitting, and the spots wiped right off.
 
dirc said:
thanks Larrin Larrin - I thought I understood (from your earlier article) that with steel with chrome, that as you lower the hardness you also improve the chrome % in solution, which helps prevent rust

from your article: https://knifesteelnerds.com/2019/01/14/which-knife-steels-have-the-best-corrosion-resistance/

"First of all, ZDP-189 achieves very high hardness levels, which usually means that less chromium is in solution"

...nuance is a b*tch ; )
Click to expand...
Yes that is when comparing different steels. A steel with high chromium in solution (more stain resistance) can only get so hard because of higher retained austenite. For a given steel to get more corrosion resistance you want to austenitize higher so that more chromium carbide is dissolved. More carbide dissolved means more carbon in solution for more hardness. In either case the limit is often retained austenite. Too much carbon/chromium in solution will mean too much retained austenite, even with cryo. At that point hardness and strength goes down, RA can convert during use leading to poor toughness, the steel is less magnetic which can be a problem depending on production method, etc. You definitely don't want a bunch of RA.
 
tiguy7 said:
I haven’t tested the ZDP for hardness, but given the edge holding, I don’t suspect that it is lower than advertised. I have experienced some spotting (surface rust) on both the 420 and the ZDP, but it was surprising that there was more spotting on the 420 than the ZDP. There was no pitting, and the spots wiped right off.
Click to expand...
arm-chairing it here, my experience with 420J2-clad ZDP189 was a CalyIII, and the cladding surface is a lot wider for exposure to the elements than the ZDP core. I never experienced any corrosion on either but the ZDP inside the spydie-hole did take on a darker hue indicating passivation from the air, this was not evident on the exposed section at the edge.

You can kinda see the darker line in the hole in this image, and the next shows the entire blade - had to tilt the knife properly to visualize the core, there was no sign of it darkening, never did I attempt to corrode it however:

592JFrO.jpg
1KPYkLQ.jpg
 
brownshoe said:
The stainless cladding may not be for rust. In the early years of ZDP, it was stated by some companies it was to lower the cost of the blade and increase the blade's (not edge) toughness.

I get William Henry e-mails, and the one for today features a knife with a blade made from "William Henry's patent pending Wave Damascus features a ZDP-189 core (HRC 67) clad with alternating layers of stainless steel and nickel silver. The billet, 45 layers in all, is patterned with a custom die to create the undulating waves that emerge across the bevels of the blade. This material can be dark-etched for contrast, or etched and re-polished for a more subtle pattern." They have claimed a ZDP hardness of about 67 for at least 15 years and based upon performance of my knife, I'd say it's greater than every steel in my stable, hardest being O1, L6 and M390 at 60-62.
Click to expand...

tiguy7 said:
I haven’t tested the ZDP for hardness, but given the edge holding, I don’t suspect that it is lower than advertised. I have experienced some spotting (surface rust) on both the 420 and the ZDP, but it was surprising that there was more spotting on the 420 than the ZDP. There was no pitting, and the spots wiped right off.
Click to expand...

I am not questioning what you guys are seeing in your use. You experience what you experience, but you can't generalize it to the steel or really question the testing done in the article. Every steel grade/type has a performance window and the heat treat plays within that performance envelop. You can't make one steel into another with heat treat, this is why we have different steels. ZDP-189 can't be very tough, relatively speaking. Geometry can rectify this a lot, but then you'd get an edge that cuts poorly, again relatively speaking. You also can't make it into a steel that is more corrosion resistant, than a steel that is known to be very corrosion resistant. I am assuming that nothing weird was done to 420J2. The cladding could be for other reasons than corrosion resistance, but 420j2 is very stainless in general.
 
I don’t think that the 420 as used by W/H is either 420j2 or 420HC. A relatively ductile cladding like 420 could prevent a harder blade from snapping off.
When comparing the effects of corrosion on different materials, I evaluate based on spots per unit area of each material not per blade.
 
I've bought and sold lots of knives made from ZDP. I think the issue is how the alloy is hardened. If it's in the 60 to 62 Rc range it might begin to get brittle. If it's near 68 Rc you can bet it will chip. Not all alloys need the same manufacturing processes.
 
tiguy7 said:
I don’t think that the 420 as used by W/H is either 420j2 or 420HC. A relatively ductile cladding like 420 could prevent a harder blade from snapping off.
When comparing the effects of corrosion on different materials, I evaluate based on spots per unit area of each material not per blade.
Click to expand...

Current san mai ZDP-189 core blades have 420J2 as cladding. I don't know if this has always been the case, but it is very likely. From W/H website

"William Henry worked closely with partners in Japan to develop a laminate that captures a 'core' center layer of ZDP-189 (HRC 67) within softer layers of 420J2 stainless steel for our blades. The ZDP creates the razor sharp edge, while the softer layers offer tensile strength and support."

Doesn't this acknowledge that ZDP-189 at HRC 67 is brittle, relatively speaking? Or are you claiming that the blade made out of hard ZDP acts differently from an edge made out of the same material? When using a knife, the edge is subjected to all sorts of forces including lateral, a thin edge of a tough steel would bend or deform, a less tough steel might instead break, crack, chip. This is a simplification to make a point. ZDP-189 at 67 HRC is brittle relatively speaking, compared to many other steels used in knives, just because you haven't seen chipping in your use, doesn't prove that the steel is not what it is or that W/H found some magic heat treat to change ZDPs parameters.
 
ace said:
Current san mai ZDP-189 core blades have 420J2 as cladding. I don't know if this has always been the case, but it is very likely. From W/H website

"William Henry worked closely with partners in Japan to develop a laminate that captures a 'core' center layer of ZDP-189 (HRC 67) within softer layers of 420J2 stainless steel for our blades. The ZDP creates the razor sharp edge, while the softer layers offer tensile strength and support."

Doesn't this acknowledge that ZDP-189 at HRC 67 is brittle, relatively speaking? Or are you claiming that the blade made out of hard ZDP acts differently from an edge made out of the same material? When using a knife, the edge is subjected to all sorts of forces including lateral, a thin edge of a tough steel would bend or deform, a less tough steel might instead break, crack, chip. This is a simplification to make a point. ZDP-189 at 67 HRC is brittle relatively speaking, compared to many other steels used in knives, just because you haven't seen chipping in your use, doesn't prove that the steel is not what it is or that W/H found some magic heat treat to change ZDPs parameters.
Click to expand...
ZDP at 65+Rc is a LOT harder than blades at only 62 Rc. What makes a material brittle vs ductile is its behavior once it reaches failure - based on the added hardness of the ZDP edge, failure is further off for it than for softer steels unless you subject it to impact trauma. Again, failure occurs when you bend/stretch/compress the edge out of alignment and this is a lot harder to do with a higher rockwell edge - that added apex strength covers for lack of toughness in impact tests.

I never experienced any chipping in my ZDP CalyIII. For most of us, the Charpy toughness values are basically irrelevant until you get into "heavy use" i.e. significant amounts of force or impacts ("heavy"). If you follow the trend-line of AEB-L on Larrin's charts, ZDP looks to be exactly where you'd expect AEB-L to end up if it could reach that hardness. Is it brittle for a knife steel with 30% carbide volume at 65+Rc? Is it brittle for a knife steel with 2% carbide volume at 65 Rc? Finally, does it deform in use compared to other blade steels commonly used? In my experience, no it does not. What I liked about ZDP was the high hardness - that ability to take and maintain a fine edge without deformation (yes, it can take a very keen edge). Chipping has rarely been an issue in my smaller knives. If someone would like to show us some cutting with ZDP that induces edge-damage in it but not in, for example, S30V at 60+Rc - cutting wire and cans, as an example, please do so. "Brittle" has a connotation of "weakness", but ZDP at 65 Rc is anything but weak. But in a thin sheet that might bend under leverage (like a knife blade) cladding it in a tougher material to increase the thickness (and so stiffness) of the blade will prevent it from bending and ever reaching failure under normal use - that's what the cladding is for.

I don't doubt the charpy tests nor the corrosion tests, I always understood that ZDP wasn't really "stainless" but have been surprised that it resists corrosion so well - better than my INFI and some others, but surface finish makes such a big difference in resistance that it requires a controlled test like Larrin's to declare a comparison. If Larrin had used well-polished surfaces, no doubt the results would have been tighter, i.e. the ZDP and many even less resistant steels would demonstrate prolonged resistance to corrosion compared to themselves with a rougher finish, but that was not his point.

I don't find ZDP "over-rated", but perhaps that is because I wasn't aware of any hype about it being 'stainless'. *shrug* I liked using it, I have no issue encouraging others to try it as well. Good stuff, takes a keen edge, holds it well, is very hard, don't mistreat it. :thumbsup: I'd like to see it compared to CPM-M4 or even just basic M2 tool steels at high hardness.
 
ace said:
Current san mai ZDP-189 core blades have 420J2 as cladding. I don't know if this has always been the case, but it is very likely. From W/H website

"William Henry worked closely with partners in Japan to develop a laminate that captures a 'core' center layer of ZDP-189 (HRC 67) within softer layers of 420J2 stainless steel for our blades. The ZDP creates the razor sharp edge, while the softer layers offer tensile strength and support."

Doesn't this acknowledge that ZDP-189 at HRC 67 is brittle, relatively speaking? Or are you claiming that the blade made out of hard ZDP acts differently from an edge made out of the same material? When using a knife, the edge is subjected to all sorts of forces including lateral, a thin edge of a tough steel would bend or deform, a less tough steel might instead break, crack, chip. This is a simplification to make a point. ZDP-189 at 67 HRC is brittle relatively speaking, compared to many other steels used in knives, just because you haven't seen chipping in your use, doesn't prove that the steel is not what it is or that W/H found some magic heat treat to change ZDPs parameters.
Click to expand...

Thinner sections of hardened metal are drastically more flexible than thick ones. So having a thinner core of high hardness steel supported by softer cladding means that the core steel is able to flex more without cracking. This used to be done with American, English, and Nordic scythe blades, which had a high carbon steel layer of edge steel laid next to a medium carbon spring steel to support the back, clad between layers of iron for toughness. Laminated scythe blades were run at very high hardness, some of them verging on the glassy side, and with very low edge angles of only about 7-9° per side. But when laminated in this manner they were more than tough enough to survive after being horribly abused by unskilled mowers. Thanks to the edge steel layer being very thin in them, such blades are often able to be badly twisted and bent without cracking, and can be straightened back out without the need for heating and re-treating the blades, all while enjoying the edge stability and increased wear resistance of the high hardness edge. :)
 
You must log in or register to reply here.
Back
Top