The on-going Stretch 2 review thread: Rust Review!

[Ben_1323]

Well, you've convinced me to get a Stretch as my next knife.

[spoonrobot]

Stain Testing!

Hey guys! Let's see if we can get some staining going on!

To mimic a quick lunch break I applied various substances to the blades and then let them sit for 4 hours. This is a situation I have experienced before. I get a lunch break and have to hurry and eat with no time to really clean my knife. After the 4 hours I removed the substances with soapy water and checked for staining. The three substances were pineapple juice from fresh cut pineapple, Yellow Mustard and Tomato Sauce.



The three knives are a VG-10 Delica 4, a ZDP189 Endura 4* and a ZDP189 FRN Stretch. The knives were cleaned to remove any oil from the blade before application of the substances.



Here are some pH levels I've found using Google, not sure of the accuracy so if anyone knows of a better source, please chime in.
Pineapple: pH of 3.20-4.00
Tomato Sauce: pH of @4.00
Yellow Mustard: pH of 3.55

Cutting the pineapple:


The knives at the beginning of the test:


Here's what I found:

1: Delica 4 VG-10 (control steel)
Pineapple? No
Tomato? No
Mustard? Yes, the stain is much fainter than the other two blades and has very little coloration. Staining was easily removed with Mother's Mag & Aluminum polish rubbed on the spot with a Q-tip for 30 seconds or so.



2: Endura 4 ZDP189
Pineapple? No
Tomato? Yes, the tomato caused no discoloration but the portion it covered can be seen when the knife is held at certain angles to the light.
Mustard? Yes, The staining occurred both on the edge and the saber portion of the blade. The edge was significantly darker than the saber, with the darkest portion corresponding to a rough area from the medium stones that was missed by the fine stones during sharpening. I do not feel this darker area is rust, application of steel wool did not remove it. This may lend credence to the idea that staining can be dependent, to some degree, on the blade polish




3: FRN Stretch ZDP 189
Pineapple? No
Tomato? Yes, the same as with the E4.
Mustard? Yes, this knife exhibited moderate staining and some rust spotting on the flat grind of the blade. The staining was darker and more obvious on the edge.



Here we can see the discoloration from both the mustard and tomato. Note the staining only occurs where the tomato contacted the blade and not from the sauce.


Tomorrow I'll see if I can remove the staining with either ACV of polishing with various chemicals.

:)


*Note that the Endura 4 was given an Apple Cider Vinegar patina several months ago, this may or may not have contributed to staining resistance. Recalling that I did a mustard test prior to the ACV I feel the staining is almost exactly the same as it was before the ACV patina process. So the ACV made no difference in respect to the Mustard, and I suspect the other substances.

[Fred Sanford]

Awesome thread spoonrobot! Perfect testing and stuff. I know from personal experience it's not easy to do all this stuff and also take pictures all the time too.....so thanks for doing that.

[JNewell]

Excellent real world test! :D We want to see pickles next.

[bdbender]

Thanks for all the hard work regarding stains. My question, with no disrespect whatever intended, is does it matter? Does the staining affect the function, sharpness, or life expectancy of the various steels in any way that you can see?

One of my chinese mules is working for a living in the kitchen knife rack, and it has a few stains now, but no other seeming consequences. Same deal with my laminated Caly3 - a stained area in the ZDP189, but no effect on function that I can see.

[spoonrobot]

Other than aesthetics I didn't think it mattered very much. I did the test because I was curious and it is always mentioned when the subject comes up with no real references.

However, after dunking the SFRN blade in apple cider vinegar for 4 hours to remove the staining (which it did quite nicely) I resharpened the blade on my Sharpmaker and then cut up some cardboard.

After only a few cuts I noticed that the edge was chipping extremely badly, worse than anything I've ever seen. This appears to have been caused by corrosion during the ACV bath. So, what did I learn? Corrosion from acidic liquids, dependent on time, may cause significant weakening of the edge structure that won't show up until the knife is used. Now, I'm unsure if this would manifest itself in "real-time" (similar to the much maligned Cliff Stamp D2 wet carpet testing) during use.

It's just another data point for my use of the steel.

[dc50]

spoonrobot Thanks for all the testing/sacrificing of your knives.
You've done a service for us, who are afraid or not willing, to test our knives as you have. good stuff! MOST

[SmoothOne25]

i noticed my stretch frn se is rattling a little? you have to really shake it but i dont see any loose parts or anything to suggest something is wrong. im a little worried. i am gonna make a thread cause its been a while and may not be able to return it weeks and weeks later.

[Donut]

Hello everyone, first post here. I've been lurking for weeks, maybe months.

My question: I read a very long review a few weeks ago, it was of either the Delica ZDP or Endura ZDP. I tried to find the review a few days ago to post this question then, but I couldn't find it and I gave up instead.

The reviewer did a really good job and there was a LOT of cutting done for the review, it seemed like they cut until it needed sharpening, then sharpened at least a few times. They did a head to head of the same model versus the VG-10 version of the same knife.

The review came to the conclusion that the ZDP held its edge slightly longer than the VG-10 did, but shortly after the edge was lost the ZDP ended up performing identical to the VG-10. They came to the conclusion that there was an inconsistency of hardness in the ZDP blade steel because it is made from a powder. They thought that the blade ended up having duller and sharper sections because of this inconsistency.

I just wanted to know if you saw the same behavior?

Thanks.

[npueppke]

Hello everyone, first post here. I've been lurking for weeks, maybe months.

My question: I read a very long review a few weeks ago, it was of either the Delica ZDP or Endura ZDP. I tried to find the review a few days ago to post this question then, but I couldn't find it and I gave up instead.

The reviewer did a really good job and there was a LOT of cutting done for the review, it seemed like they cut until it needed sharpening, then sharpened at least a few times. They did a head to head of the same model versus the VG-10 version of the same knife.

The review came to the conclusion that the ZDP held its edge slightly longer than the VG-10 did, but shortly after the edge was lost the ZDP ended up performing identical to the VG-10. They came to the conclusion that there was an inconsistency of hardness in the ZDP blade steel because it is made from a powder. They thought that the blade ended up having duller and sharper sections because of this inconsistency.

I just wanted to know if you saw the same behavior?

Thanks.

Welcome to the Forum!

Never had a ZDP blade, but I've heard lots and lots of conflicting opinions about that steel. Most people seem to agree that ZDP excels at staying sharp when it is reground to a very acute angle, but aside from that some people say that it is a very brittle steel, some say that it performs the same as VG10, some love it, some hate it-it is a very controversial steel.

Here is a review though that seems to touch on your question:

http://www.youtube.com/user/BLUNTRUTH4U ... xKl97uCaGg

Part 2 is a cutting test where the reviewer cuts a lot of wood and cardboard until the edge gets dull. If I remember right, this reviewer came to the conclusion that ZDP is a very very tough steel which can take a beating (not brittle), but doesn't hold an edge very well.

As far as powdered steels go, if I understand it correctly the whole point of them is to eliminate inconsistencies within the metal. Instead of being melted and cast, which would allow heavier elements to settle out as the metal cools, they are 'powdered' while still liquid. I'm not sure what the exact process is, but from my understanding the molten metal is literally blown apart using some kind of compressed gas, and the resulting globlets are dropped down a shot tower, similar to the way ball bearings are produced. The results is a whole bunch of uniform little balls of steel because the balls cool in free fall. Not really sure where the terminology "powdered" came from so if this is an incorrect explanation please correct me.

In order to retain uniformity within the metal this 'powder' can't be melted again, so presumably it is then rolled into slabs and cut into bars. I'm not really clear on this part either because it seems to me that this would result in an extremely non-uniform metal, but for sure the goal of powdered steel is uniformity.

[gunmike1]

If someone is losing their sharper edge really fast and basically having identical performance to VG-10 with ZDP-189 they probably had a burr. On identical blades ZDP 189 will have a very large and noticeable difference cutting EDC things like cardboard, rope, ect. It will also take a much more acute edge without a problem. VG-10 is excellent steel, but when sharpened correctly ZDP-189 has much better edge retention in my experience.

Mike

[Bill1170]

Welcome to the Forum!
As far as powdered steels go, if I understand it correctly the whole point of them is to eliminate inconsistencies within the metal. Instead of being melted and cast, which would allow heavier elements to settle out as the metal cools, they are 'powdered' while still liquid. I'm not sure what the exact process is, but from my understanding the molten metal is literally blown apart using some kind of compressed gas, and the resulting globlets are dropped down a shot tower, similar to the way ball bearings are produced. The results is a whole bunch of uniform little balls of steel because the balls cool in free fall. Not really sure where the terminology "powdered" came from so if this is an incorrect explanation please correct me.

In order to retain uniformity within the metal this 'powder' can't be melted again, so presumably it is then rolled into slabs and cut into bars. I'm not really clear on this part either because it seems to me that this would result in an extremely non-uniform metal, but for sure the goal of powdered steel is uniformity.

The manufacturing of powdered steels involves creating an aerosol of microscopic droplets of the molten steel which are then frozen into a fine dust, or "powder." This steel powder is then gathered up and pressed under high heat and pressure to make bars of steel. Sintered, if you will. The heat is less than the heat needed to fully melt the steel, so the component elements stay evenly distributed throughout the bar.

Bill

[npueppke]

The manufacturing of powdered steels involves creating an aerosol of microscopic droplets of the molten steel which are then frozen into a fine dust, or "powder." This steel powder is then gathered up and pressed under high heat and pressure to make bars of steel. Sintered, if you will. The heat is less than the heat needed to fully melt the steel, so the component elements stay evenly distributed throughout the bar.

Bill

Thanks for the explanation, that makes sense. I didn't really understand how you would end up with a solid metal after you ended up with a powder, but that (plus reading up on sintering) makes sense. I guess I also didn't realize that you could disperse molten steel into droplets that small because I imagined it to be too sticky and viscous. Pretty ingenious process, really.

[JaM]

I'm not too scared about staining though, I have an E4 in ZDP (SE) who serves me well.
However, I'm not too sure about the sharpening of said steel.
I can handle VG-10 quite well with the sharpmaker, just as I can sharpen S30V and the "byrd" steel. AUS 8 isnt a problem either.

I do like the handle colour (blue) of the ZDP-version, and I probably like the feel of the knife. Having one in a CE would be nice, as a "come-along-on-this-small-hike/camping knife".
It would also be used in the kitchen, competing with the E3 in CE I have there (probably replacing it..?).

So the big question for me would be: ZDP-189 or VG10 ?
What would YOU advise ? :)

JaM


Oh, and thanks for this thread, and the testing. Interesting stuff ! It probably convinced me to get the Stretch instead of the Manix 2. Apart from the weight-factor.

[spoonrobot]

Little update: :)

Back at the end of March I took a trip to the white, sandy beaches of Pensacola, Florida.

While I was there I spent most of a day in and out of the seawater with the ZDP S2 clipped to my trunks. After several hours I was able to rinse the knife with fresh water but was not able to fully clean or lubricate the knife until several hours after that. The knife was not treated in any way, there was some residual motor oil (used for lubrication of the pivot) in the pivot area but no other lubricants were present on the knife. The only rust was observed on the liners and a very small amount on the tang of the knife. Overall I was amazed at the lack of corrosion on the actual blade. The edge was completely rust free and did not appear to have lost any sharpness. I did not notice the massive chipping during use after exposure that came from the ACV bath either, it appears that salt-water based corrosion (or the lack thereof) does not affect the edge in that manner.

The corrosion present after exposure.


So, the susceptibility to corrosion is overstated in the very least that seawater appears to have little effect on the blade steel and actually causes more issues with the liners. In this same vein and somewhat anticlimactically, my FRN S2 ended up clipped to my trunks while I went on a swimming trip to a freshwater lake. After an entire day of in and out water activity it was found that there was no corrosion any where on the knife. No as impressive as the beach trip but still quite interesting to see.

[Splice]

that's pretty crazy that the blade didn't rust whatsoever in salt water but that the liners did.

This information is really cool- I really appreciate what you're doing here!

[Fred Sanford]

Excellent info Spoonrobot!

I have to agree with you. I've been carrying a Caly 3 in ZDP-189 laminate and it's 88 degrees and humid here. It was in my pocket mowing the lawn and doing outside stuff and the exposed ZDP steel never gets any spots of rust or anything. It patinas a little bit but that's about it.

Great stuff.

Thanks for your valuable opinions.

[Blerv]

Thanks for the update :) .

[spoonrobot]

Since my technique has changed a little here's the current sharpening technique I'm using.

If I'm going to rebevel the edge I begin with the 11" Norton medium crystolon stone. I use light pressure and make sure that I'm as consistent as possible with the angle so sharpening time is as efficient as possible.

Once I raise a burr on both sides and am satisfied with the angle I will move to the 11" Norton fine india stone. Same technique as above; light pressure and as consistent with the angle as possible. It's important to spend time and attention on the edge area closest to the pivot. This area is very easy to ignore and you may find the rest of the knife is at the correct angle but the first 1/2" is not sharpened correctly. The abrasion resistance allows you to go back and correct this without messing up the rest of the bevel. You can move the knife down the stone without moving it along the edge and fix it but it's generally easier to be aware of this and accommodate it beforehand.

Once I've gotten a burr on both sides I'll remove it with the Sharpmaker, generally with the white flats are 30 degrees. After the burr is removed as much as possible I'll use the some of the chromium oxide on a short section of leather belt to remove the micro-burr left by the Sharpmaker. I prefer my edge to be on the coarse side of a fine polish so I generally make less than a dozen strokes total, checking for progress with a flashlight or microscope and will stop as soon as the micro-burr is gone.

I'll generally check the edge by shaving or push cutting newsprint. It's good to go when shaving requires no pressure and push cutting can be done without moving the edge at all.


If the edge requires maintenance I'll use the Sharpmaker, 30 degrees with the white flats, it only takes a few strokes per side until the edge gets it's bite back and then I strop as above.

This seems to be working the best for my uses. Edge retention is very good, I can generally go a week and a half to two weeks before I need to touch up. This is with moderate use and cutting things like cardboard, food prep and general use EDC chores. Durability seems good as well, I've accidentally hit staples or other metal/steel items when cutting and the edge has suffered no damage. All in all, I've very satisfied with the steel!

[A.P.F.]

Thanks for the great pics and ongoing reporting, Spoonrobot!