Observations on edge retention of some stainless alloys using a visual inspection tec

dextersp1 said:
Any insights available?

Basically, I'm trying to understand how much better is a 10.5 vs a 7?

Can I get 50% more use (before requiring sharpening) with a 10.5 vs a 7 or 5% (that type of info)?
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Sorry, the technique is qualitative only. It is not quantitative.
The most I can say is that the difference between any two adjacent alloys in the chart are noticeable to me in my everyday use. For instance, I actually do notice the difference between 9Cr13CoMoV and 8Cr13MoV in every day use.

Phil Wilson uses a quantitative test technique. Since you are a registered user and cannot search, you might want to do a Google site search for posts by Phil Wilson. I know he has commented about his results before.
 
Thanks for posting your results -- and for taking such care in producing them. I am surprised that you limit your examination of the edge to 3x magnification. You'd see so much more with 10x or 12x, and that level of magnification is not expensive.
 
There are many things that I like about your test. For one thing you pick some of the same knives as I have purchased in my efforts to compare steels. I would suggest that you try the same measurement techniques using a more abrasive wear medium. I would use cardboard in place of the manila rope. Since you are not measuring cutting effort I don't think that the drag effects of the cardboard would make your wear sensitive to blade profiles. I would try and find some convenient material similar to the backing for pads of legal paper. I personally cut a lot more cardboard than rope and it seems useful.
 
Twindog said:
Thanks for posting your results -- and for taking such care in producing them. I am surprised that you limit your examination of the edge to 3x magnification. You'd see so much more with 10x or 12x, and that level of magnification is not expensive.
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I have tried higher magnification. At higher magnification, I just see a little part of the blade at a time and it becomes hard to get an overall sense of how it performed. At 3 to 5 I see more of the blade at a time. This is helpful because I am going back and forth between blades to compare them.



Jeff Clark said:
There are many things that I like about your test. For one thing you pick some of the same knives as I have purchased in my efforts to compare steels. I would suggest that you try the same measurement techniques using a more abrasive wear medium. I would use cardboard in place of the manila rope. Since you are not measuring cutting effort I don't think that the drag effects of the cardboard would make your wear sensitive to blade profiles. I would try and find some convenient material similar to the backing for pads of legal paper. I personally cut a lot more cardboard than rope and it seems useful.
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Hello Jeff,
That is a good point that I am not measuring force so I could worry less about the blade profile and use cardboard. I'll have to think about that.

We both like user knives. I admit that I bought some of them just to try that particular alloy, but at the end of the day they are all good users. They pretty much all get pocket time.

Warm regards from a fellow former Devil's Gate denizen,
Frank
 
The "super steels" are more marketing than anything, that being said, EVERYTHING is marketed to make us buy, buy, buy.

Why would anyone spend $5,000 for a diamond, when it would take a jewelers loop to see the difference between it and CZ? Because we know it's a diamond, it's perceived value to us is much higher.

Based on your chart, it would probably be possible to create value chart based on the average price for a knife using that particular steel. It would take a lot more research of different brands and models, but it could be done.

Thanks, now I feel better about 440C. It's old and cheap, but still gets the job done. Somewhat like myself:)
 
Off topic, but I was just exchanging emails with a guy who went to LaCanada HS about his garage band fellows from the latter 1960's. He lives in San Diego these days.
 
Thanks for your excellent work, knarfeng, and thanks for sharing it. It is a pleasure to see someone that knows the difference between 'qualitative' and 'quantitative'. I found your evaluation to be both simple and intuitive, with results that I am sure most experienced users would agree with.
 
You might make your test more quantitative if you vary the number of cuts and use each blade up to a fixed level of visible wear. If you select a level of visible wear that correlates with when you would consider it to need touch up (some minor sharpening intervention) your number of strokes would represent edge retention directly. You could keep a reference "dull" blade to visually compare edge wear status. Since you would be going for a match rather than relative appearance you could probably be more accurate.
 
Jeff Clark said:
You might make your test more quantitative if you vary the number of cuts and use each blade up to a fixed level of visible wear. If you select a level of visible wear that correlates with when you would consider it to need touch up (some minor sharpening intervention) your number of strokes would represent edge retention directly. You could keep a reference "dull" blade to visually compare edge wear status. Since you would be going for a match rather than relative appearance you could probably be more accurate.
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great idea!!!
 
A tangential point re. a test with equal edge angles, but this test got me thinking (oh oh). If you did this test on two identical knves, one edge at 50 degrees and one at 25 degrees, which one would exhibit less edge deformation or wear after XX cuts? Or which edge will deform first with a given cut, a 0.5 micron diameter edge, or a 5 micron diameter edge? In my mind the correct answers are intuitive.

Does this contradict the oft stated mantra that the thinnest and/or sharpest knife will have the best edge retention? Some of you will remember some brouhaha's over this exact point.

I think both can be true depending on how you define edge retention. How you measure sharpness, blunting, or cutting ability and whether you are testing with equal or unequal geometry will make the difference. Just an illustration of how ill-defined yet commonly used knife parameters can make a common technical understanding difficult.
 
Broos said:
A tangential point re. a test with equal edge angles, but this test got me thinking (oh oh). If you did this test on two identical knves, one edge at 50 degrees and one at 25 degrees, which one would exhibit less edge deformation or wear after XX cuts? Or which edge will deform first with a given cut, a 0.5 micron diameter edge, or a 5 micron diameter edge? In my mind the correct answers are intuitive.

Does this contradict the oft stated mantra that the thinnest and/or sharpest knife will have the best edge retention? Some of you will remember some brouhaha's over this exact point.

I think both can be true depending on how you define edge retention. How you measure sharpness, blunting, or cutting ability and whether you are testing with equal or unequal geometry will make the difference. Just an illustration of how ill-defined yet commonly used knife parameters can make a common technical understanding difficult.
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That's one of the reasons I set all my knives at exactly the same angle when I test them.

I think that the results you get with different angles are going to vary depending on the cutting job as well. When I use my knives for odd jobs out in the yard cutting hard substances, I often find that what works best for me is a broader edge angle. Whereas, if all I am doing is something like slicing cardboard, then thinner is better.



I have a couple of things in mind to try in the future. One of them is to compare two knives of the same alloy at the same hardness but with different edge angles get a feel for the differences you mention.

Another is to get different blades of the same alloy at different hardnesses. This will likely be AUS8 because I have seen different producers publish fairly different hardness specs for this alloy. I think it will be possible to compare a 56HRC to a 60HRC. I'd like to get a feel for variations in carbon content vs. variations in hardness.
 
Jeff Clark said:
You might make your test more quantitative if you vary the number of cuts and use each blade up to a fixed level of visible wear. If you select a level of visible wear that correlates with when you would consider it to need touch up (some minor sharpening intervention) your number of strokes would represent edge retention directly. You could keep a reference "dull" blade to visually compare edge wear status. Since you would be going for a match rather than relative appearance you could probably be more accurate.
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I maybe could do that, but hitting exactly the same amount of deformation exhibited by the standard would be an iffy proposition. Almost impossible not to go over or under. You should pardon the expression, but, repeatability would be a cast iron B. I don't think I'd have the patience for it.

As it is, just comparing a set of blades after a given number of cuts takes several runs at it until I am sure I get the sequence of damage correct between them.
 
A.P.F. said:
Thanks for your excellent work, knarfeng, and thanks for sharing it. It is a pleasure to see someone that knows the difference between 'qualitative' and 'quantitative'. I found your evaluation to be both simple and intuitive, with results that I am sure most experienced users would agree with.
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Thank you sir.
 
Are you slicing or push-cutting? Different steels respond differently to different types of cutting. The higher carbide steels have better abrasion resistance so they have excellent edge retention when it comes to slicing, but are outperformed by simpler (less carbides) steels when it comes to push cutting.

High carbide steels with lots of carbon also have poor edge stability. I reprofile them to 4° degrees per side and the edges don't hold up as well as the simpler steels. These are special straight razors that I use for shaving, where extreme acute angles are useful. For this application, steels with less carbides tend to be finer grained and simply work better.

I have a simpler test for slice-cutting edge retention: by how difficult the steel is to sharpen, and how soon the edge becomes polished as I move up the grits. But since cutting is a combination of slicing and push-cutting, and blade profile, it doesn't tell the whole story obviously.
 
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Great tests, thanks for posting them! Knife testing is a whole lot more work than most realize until they try it!
 
cotdt said:
Are you slicing or push-cutting? Different steels respond differently to different types of cutting. The higher carbide steels have better abrasion resistance so they have excellent edge retention when it comes to slicing, but are outperformed by simpler (less carbides) steels when it comes to push cutting.

High carbide steels with lots of carbon also have poor edge stability. I reprofile them to 4° degrees per side and the edges don't hold up as well as the simpler steels. These are special straight razors that I use for shaving, where extreme acute angles are useful. For this application, steels with less carbides tend to be finer grained and simply work better.

I have a simpler test for slice-cutting edge retention: by how difficult the steel is to sharpen, and how soon the edge becomes polished as I move up the grits. But since cutting is a combination of slicing and push-cutting, and blade profile, it doesn't tell the whole story obviously.
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The answer to your question was in my first post in the thread.

knarfeng said:
...
Before I cut, I mark off a 2” length of blade. I use that 2” length to make a slicing motion through the rope. So, it is 2” of steel that is the same hardness, the same edge angle, and the same sharpness that is cutting the rope. I make 20 such cuts with each blade.

I do this with anywhere from 3 to 5 alloys at a time.

After I make 20 cuts using each blade that is in a test run, I ...
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I tend to agree with your comments on carbides and edge bevel angle, although I have not encountered the phenomenon at the coarser angles that I use on the alloys I have tested. There is an engineer from Sandvik who posts here (razorsharp244). He has stated that most Sandvik alloys eschew carbides because of edge stability reasons. IIRC, he said there is no absolute proof of it happening, but it is a theory that successfully explains observed results. Here is a great read on the topic.
http://www.bladeforums.com/forums/showthread.php?t=561622

However, it is not clear to me that blades made from high carbide alloys are automatically outperformed in push cutting by blades made from alloys with no carbides. I have blades in low or zero carbide steels that I EDC and I do not notice them outlasting my higher carbide steels in my everyday usage. I think that zero carbide steels are better for some applications. But you have to define the application.

It is well that you defined what you use a 4° beveled blade for cutting. Most folks don't use a 4° bevel because the resulting blade is so thin that the steel deforms when performing most common cutting tasks. I feel the same way about edge angles that I do about alloys: There isn't a single one that does everything perfectly well. Most folks sharpen to an angle between 15°-25° and those angles work for most applications. I'm not certain that you would really observe the carbide tearing out phenomenon at those angles, so for most folks, the issue does not exist.

I agree you can get a feel for the wear resistance of an alloy by how it responds to a sharpening stone. But then you also have to consider the thickness of the blade. The thicker the blade, the more area has to be beveled and the more resistance to sharpening the blade will have. This can lead to incorrect assessments.
 
Great post, knarfeng! Your visual inspection technique is very useful. I will continue doing research on knife steels that perform well with acute angles.
 
Great tests, Knarfang. As Sodak said it is a ton of work to do knife testing, much more work than people think, and I think we have all learned some good info from your tests. AUS-8 at different harnesses would be a good test, as my CRKT's were 56-57 and burred very bad, while properly heat treated AUS-8 can be good stuff from what I have heard. I have a couple knives in higher carbide steels (CPM D2 and S30V) if you want totry those. The S30V is 59 RC, but my CPM D2 Millie hasn't been tested yet.

Mike
 
Very nice test!

Perhaps the reason I never really "took" to my ATS34 Gerber AF Covert was because since I can't sharpen very well it was never sharp because it's tougher TO sharp....
 
Maybe the reason I never much liked my ATS-34 Gerber AF Covert was because I couldn't sharp it as it was so much tougher TO sharpen...

Thanks for the testing!!!
 
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