Digging sprinkle out with Yuna Hard II ZDP-189 (video)

nozh2002

nozh2002

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http://www.youtube.com/watch?v=O0PHxVP6WSo

I was replacing sprinkler and use Yuna Hard II with ZDP-189 blade (actually clay ATS-34+ZDP-189+ATS-34). I was doing this for different reasons - at first there are many roots in this ground and so with shovel I had to use some force, which I rather avoid, because I afraid to cut sprinklers pipes. So it need to be delicate digging and root cutting - knife is only solution I know.

I pick Yuna Hard because it is my most expensive folder and I still need an excuse for this - this is one reason and another one - I heard some complain about ZDP-189 being brittle. On my experience this is not a case and to prove it I cut aluminum corners, drywall, hardwood, computer paper (500 sheets) etc...

Here is roots in dirt and no signs of chipping. Edge of course got dull, but it take me 5-10 minutes to fix it, and make it back hair whittling sharp.

Thanks, Vassili
 
Nice video. ZDP doesn't seem that chip prone, although it's not a tough steel. The task you did wasn't very demanding, though. Chopping twigs would be a more suitable task to test for chipping.
 
cotdt said:
Nice video. ZDP doesn't seem that chip prone, although it's not a tough steel. The task you did wasn't very demanding, though. Chopping twigs would be a more suitable task to test for chipping.
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It is probably not as tough as S7, but among stainless steels for knives at 65HRC it is very tough. Of course toughness is not as important for knives as edge holding, after all knives suppose to cut and ability to be used as a prybar important only if it can cut at first place. So far tough steel knives does not cut very well.

I guess at some point some turn attention to steel toughness - which is important property for knife, but then it take full attention. So we have knives which are very tough - can be used as prybars, as choppers... etc, but not too good at cutting.

But what is you source of information? What does mean - ZDP-189 is not tough steel? I consider it pretty tough, again based on cutting roots, aluminum, drywall etc - what is your statement based on? I hope it is not only reading for books and forums.

Thanks, Vassili.
 
nozh2002 said:
It is probably not as tough as S7, but among stainless steels for knives at 65HRC it is very tough. Of course toughness is not as important for knives as edge holding, after all knives suppose to cut and ability to be used as a prybar important only if it can cut at first place. So far tough steel knives does not cut very well.

I guess at some point some turn attention to steel toughness - which is important property for knife, but then it take full attention. So we have knives which are very tough - can be used as prybars, as choppers... etc, but not too good at cutting.

But what is you source of information? What does mean - ZDP-189 is not tough steel? I consider it pretty tough, again based on cutting roots, aluminum, drywall etc - what is your statement based on? I hope it is not only reading for books and forums.

Thanks, Vassili.
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Based on Hitachi's steel brochure, Hitachi doesn't seem to think it's very tough:

hitachisteels2.gif


Now there is a difference between toughness and chip resistance. The ZDP-189 being very hard actually makes it more chip resistant because it doesn't "yield" as easily. The blades that do chip do so because of internal stresses making it very brittle, so they can actually chip even if they are soft. ZDP-189 properly heat treated does not have this issue.

I should mention that my own knives in ZDP-189 stood up well, even though I put acute edges on them.
 
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Well, this kind of tables or datasheets are good reference, however they are based on common metallurgical practice. This may not be directly applicable to how knife does behave during use. This table is good to pick new steel, and may let you set expectation, but after practical use - and this steel in wide use (thanks to Sal Glesser) from Aug 2005.

So now we can really say that yes, this steel does or does not behave as it was predicted by metallurgical data provided by Hitachi.

And based on more then a year and half hard use, I can tell you that this steel is tougher then many other steel widely used in knife industry, and though to stand against anything I throw at it so far.

Thanks, Vassili.
 
Toughness is a tecnical term that describes the energy absorbed by the material at fracture. (The area under the stress strain curve.) Toughness is usually measured with a static tensile test and the toughest metals are those that can be drawn into wire (copper is one of the toughest metals.)

Notch toughness is measured with a notched specimen in an impact test (Charpy V-notch). This is the test most applicable to knives breaking and chipping.

Toughness will vary with heat treatment of the material and the ambient temperature of the test specimen.

Any knife steel will probably have low toughness compared with low carbon and low alloy structural steels. And the performance of a knife under abusive conditions will depend on more than the toughness of its materials. Strength, hardness, geometry, etc. all enter into the picture.

Steels with a low yield strength (relative to their ultimate strength) generally will undergo considerable plastic flow before fracture and will roll or dent rather than chip. (They will also usually be very poor choices as a blade material.)
 
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guyfalks said:
Toughness is a tecnical term that describes the energy absorbed by the material at fracture. (The area under the stress strain curve.) Toughness is usually measured with a static tensile test and the toughest metals are those that can be drawn into wire (copper is one of the toughest metals.)

Notch toughness is measured with a notched specimen in an impact test (Charpy V-notch). This is the test most applicable to knives breaking and chipping.

Toughness will vary with heat treatment of the material and the ambient temperature of the test specimen.

Any knife steel will probably have low toughness compared with low carbon and low alloy structural steels. And the performance of a knife under abusive conditions will depend on more than the toughness of its materials. Strength, hardness, geometry, etc. all enter into the picture.

Steels with a low yield strength (relative to their ultimate strength) generally will undergo considerable plastic flow before fracture and will roll or dent rather than chip. (They will also usually be very poor choices as a blade material.)
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Good info. How would you determine what is the optimal hardness for chip/dent resistance? The blade must be hard enough to not be easily dented, yet not so hard that it becomes brittle.
 
cotdt said:
Good info. How would you determine what is the optimal hardness for chip/dent resistance? The blade must be hard enough to not be easily dented, yet not so hard that it becomes brittle.
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That is hard question; and I don't know the answer. While a knife is not a complicated machine, there are a lot of variables in size, material, etc.

I also doubt there agreement as to what is optimal because there are so many different uses a knife may be put to and a lot of opinions about what aspect of performance is the most important.
 
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guyfalks said:
That is hard question; and I don't know the answer. While a knife is not a complicated machine, there are a lot of variables in size, material, etc.

I also doubt there agreement as to what is optimal because there are so many different uses a knife may be put to and a lot of opinions about what aspect of performance is the most important.
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...And this is why practical use is final answer. So far ZDP-189 proven to be tough against dry wall, aluminum, paper, hardwood and roots in the dirt. I also have very negative experience with "toughest" steel...

So all those tables and datasheets are good as a reference, but final word is always real world use. I do not care too much about results of static tensile test if again I can throw anything to this steel and it ask for more.

Thanks, Vassili.
 
guyfalks said:
...Strength, hardness, geometry, etc. all enter into the picture.
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Can you please tell as more about this term - strength. I thought this is same as toughness. What other properties of steel should be considered as important for knife steel.

Thanks, Vassili.
 
Vassili, Further to Guyfalks post, strength is measured by UTS (ultimate tensile strength). Usually, this has an effect in bending where one edge reaches UTS (the side in tension not the side in compression). Toughness is an energy related measure as explained in Guyfalks post. I would add that there are two levels of energy. One to initiate the crack and the other to propogate the crack. Usually in materials as hard as knife blade these are so close that the crack, once initiated, continues till it reach a crack stopper such as the other side of the blade.

I have only seen two blades where the crack did not continue through to the other side. One was in a laminated blade. The lamination join was a the crack stopper. In the other, the crack started in the sharpened edge but did not continue through the thicker section as it did not have the energy to continue in the thick part of the blade.

But there is no simple answer as most failures have some element of strength and toughness involved. Therefore it can be difficult to interpret some failures. I hope this helps. I don't want to cloud the issue for you.

Mike
 
nozh2002 said:
Can you please tell as more about this term - strength. I thought this is same as toughness. What other properties of steel should be considered as important for knife steel.
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Listing and describing all the properties and how they apply is beyond my ability. But let me try to explain the difference between ultimate tensile strength, toughness, and notch toughness in a simplified manner.

Imagine having superhuman strength and pulling apart a steel bar. The maximum force you would have to exert while pulling it completely apart is its ultimate tensile strength. Now suppose you are also a human computer capable of measuring the force you exert as you pull the bar apart (in pounds) and recording it every .01" or so of stretch. After the bar breaks you plot force, on the vertical axis, versus the amount stretch (on the horizontal axis). That area under that curve is the toughness in inch-pounds. You could have one material with a very high strength that doesn't stretch much and another that has less strength but stretches like taffy and is tougher.

Notch toughness. Imagine a glass bar. You pull it apart and find it has a high strength. But now you take a hammer and smack the bar (a new one) on the side with the minimum speed needed to break the bar. Determine the kinetic energy of the hammer (0.5*M*V**2) and you have notch toughness (and it is probably quite low since normal glass shatters easily, so a material can have relatively high strength and low notch toughness). The steel specimens are notched to get them to break consistently and readily.

The actual requirements for how to conduct the tests are much more complex and detailed than my description. But I hope this gives an idea of the basic meanings of the terms.
 
So seems like non of those properties directly applicable to knife performance. One more important for pry bar, another for axe or sword, but for cutting ability hardness and wear resistance is more important.

So best so far is hardest - ZDP-189 and most wear resistant CPM-S90V.

I guess there is some connection between toughness and strength and ability to stay sharp for long time, but it is not direct relation.

Steel microstructure of steel way more important and so Dozier D2 with his multiple tempering is the best of the best.

Thanks, Vassili.
 
nozh2002 said:
So best so far is hardest - ZDP-189 and most wear resistant CPM-S90V.
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CPM S110V is even more wear resistant. Other steels can be equally hard to ZDP-189, but Hitachi (like their other steels) recommend use of the steel to near its maximum hardness. CPM-M4 could reach up to 66-67 hrc as well but Crucible always recommends something far below max hardness for whatever reason. In my use, so long as the blade is not brittle, harder knives are actually more chip resistant because the edges don't "yield" as easily.
 
nozh2002 said:
So seems like non of those properties directly applicable to knife performance. One more important for pry bar, another for axe or sword, but for cutting ability hardness and wear resistance is more important.

...
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And where exactly does "digging out a sprinkle" enter into your scheme of applicability?
 
markksr said:
And where exactly does "digging out a sprinkle" enter into your scheme of applicability?
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I think nozh2002 is trying to demonstrate thet the knife is resistant to edge chipping. Many have complained about edge brittleness in ZDP-189 in normal EDC situations
 
Even if the edge did have small chipping you would never see it without looking a lot closer than what that video showed. Without closer inspection that video shows nothing of ZDP's performance.
 
It is clearly has not chips you may expect from brittle steel. Sorry, but this is obvious. Of course under microscope it should be some chips, but this can not justify saying that this steel is brittle.

Thanks, Vassili.
 
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