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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 4:45 am 
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"Is it possible for a german knife like wustof to be as sharp or sharper than a similar priced japanese knife of similar type?

Will it retain its edge better over a period of time? Just curious of your thoughts? Are all german and japanese created of equal sharpness?"

It's probably not wise to completely generalize German vs Japanese. There is enough variance in each group to treat this on a case by case basis. Many German knives are not as hard as many Japanese knives. This softness is certainly related to steel types, but tempering, etc are relevant here. There is also a difference between HRC values and abrasion resistance. You do have knives that are of a lower hardness than other knives, yet the presence of vanadium carbides will still produce an edge that takes more effort to sharpen.

Chromium carbides aren't a sole determinant. Take zdp-189 steel for example. This is a steel with 20% chromium - quite high, but it also has high carbon content (3%). It can take a very acute edge - I have a pocket knife of zdp-189 sharpened to 7.0 degrees per side. With very good edge retention. It can also be hardened to very high HRC values, sometimes as high as 67 HRC.

It's a bit much to summarize all of knife metallurgy in a single post :)

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Ken


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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 2:20 pm 
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Thanks Ken,

Absolutely right about the fact that ZDP will take a steep edge, but if you saw in my first post, it was stated that chromium has nothing to do with edge steepness, that's all hardness. Chromium makes big, hard, corrosion resistant carbides that don't take a "refined" edge, but can take a "steep" one (10 degrees or less) if hardened past 60, and depending on alloys... but the reason ZDP takes a fine edge with all that chromium is because of the fact that it's a powdered metal, and literally the most expensive one on the market, due to a special manufacturing technique. :ugeek:



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 3:38 pm 
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I'm not going to go into the deep metallurgy like Ken and Shaun seem to have :o but I'll add my $0.02:

I think there are two things to discuss here....edge refinement and edge profile.

I can grind the edge on a Wusthof as thin as you reasonably want a kitchen knife. But, you can't refine the edge as highly as you can with something like well HT'd AEB-L no matter how hard you try because the grain structure in that stainless Wusthof uses is not as fine as well HT'd AEB-L. So, no, you can't make a Wusthof as sharp.

Add to that the Wusthof would fail almost immediately at the thickness you can take a well HT'd AEB-L blade.

So, no, not all German and Japanese knives are made of equal sharpness.

A German knife is typically made of softer stainless steels. For the masses looking for a "high end" kitchen knife. They can be steeled like a bucking bronco, thrown in the sink without chipping, and ran through a can opener sharpener without completing destroying themselves. They can be steeled back to life reasonably with a good sharpening once or twice a year by the average home cook.



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 5:39 pm 

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Adam,

I understand edge profile and why that can make a Japanese Knife sharper than a German.. If a German knife is ground to a 15 degree edge then it will either turn into a wire edge or dull very quickly... However, can you talk about edge refinement.... Do you mean that if taken past a 2000 grit stone then it will not loose its teeth.. Would you mind explaining this further?


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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 6:22 pm 
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http://www.knifeforums.com/forums/showt ... id/809833/

At the bottom of that post on KF is a bunch of microscope pictures of the grain structure of various steels.

Not all of the pictures are to the same scale, but let's look at two distinctly different steels:

154CM:
Image

and 13C26 (I used 13C26 as it's a clone of AEB-L and it uses the same magnification rate as 154CM, while the picture of AEB-L does not):
Image

Using the graphical representation of scale, the carbides in 13C26 (AEB-L clone) are tremendously smaller and more uniform than in a steel like 154CM.

Some of the carbides in 154CM appear to be 15 micron's wide. Whereas the average carbide in AEB-L/13C26 is like 1 micron.

A more uniformly dispersed carbide structure of much, much smaller carbides results in an edge capable of higher refinement that lasts.



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 6:28 pm 
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Basically what happens in heat treat, the chromium carbides grow so large in those "lesser steels" :ugeek: that the carbides will actually be larger than the grit you are currently sharpening with. A ot of the time there will be chromiums carbides in excess of 60 microns in cheap steel, not that ALL of the carbides are that size, but the average still tends to be much bigger than better steel. The result is what we call "carbide fallout" where the big chunky carbides actually fall out of the edge and cause it to loose that "off-the-stones" feeling very fast, but then will hold a semi-refined edge for a long time after. This is the case with most cheaper stainlesses and some of the 1st generation powdered metals, but the difference is that the cheaper stainless tends to not even hold the semi-refined edge for very long either.

So, the smaller the carbides, generally the tougher the steel, it will take a higher refinement and hold it longer, generally speaking, and should come back with stropping easier. An exception to "fine carbide" to "edge holding" argument, there's another sweet-spot IMO. Instead of having the smallest carbides, you can have a sweet-spot of nice sized carbides and better alloys. SKD11 tool steel might not have the finest carbides in the world, but it still takes a good refinement, and holds very well because the Chromium content is still below 13% (keeping in mind this is NOT a powdered metal). I love tool steels because they tend to have decent sized carbides, medium chromium content, but other alloys to make them awesome.

Don't get me wrong, I'm not knocking chromium, for without it we wouldn't have stainless, and it can help make a knife harder to take a steeper edge.. given the right circumstances. :)

And I see Adam beat me to the punch. Get a life!!! :mrgreen:



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 6:41 pm 
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Just some first hand experience to share real fast with ya'll:

In my experiences, using a poly-board, 2k refinement lasts longer on most steels, but especially VG-10, then does a 4k or 8k edge. Time and time again, a poly board kills a refined edge on most steels. Not to say that 2k isn't refined in its own right, just not what some of us are used to.

Now, an end-grain board, the game completely changes. Also, using a non-stainless steel, or fine-grained stainless will give you the ability to bring the edge back more times with honing, increasing time between actual stone sharpenings.

Almost all of the knives on the site now have really good steel, or at least "mediocre" at worst (Global, Shun).. so, really, at the end of the day, the knives we recommend on this forum will generally have wicked good steel.. the only differences we look for are:

How good are your sharpening skills, and how will you be using the knife?



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 7:02 pm 
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"Get a life"?....I'll kick your your internet ass cajun youngin!! That took me about 30 minutes to write damnit!!

My sharpening skills are pretty damn good.....just so we're clear!! :o



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 8:34 pm 
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LOL, yeah, well it took me about 30 minutes to post as well, I was posting my response at the same time you were. I love hopping all over steel debates, since I'm such a steel snob and all :mrgreen:



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 Post subject: Re: Is it possible
PostPosted: Tue Apr 02, 2013 8:50 pm 
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I never said you were a steel snob....publicly anyhow!! :)



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