what steels and why

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ajhuff said:
Hmmm.... kind of casually mentions it in passing. In the context of polishing a flat surface, not really the same as a knife edge.

Also, the context I have always read is the "large" carbides pulling out of the knife edge is the pull out is noticeable. How big is a "large" carbide? I still have my doubts.

What I'd like to see is some photomicrographs of a knife edge showing the missing carbides. Actually, I would love to see ANY photomicrographs of some knife edges, especially a transverse view. Are you aware of any Larrin?

Thanks,

-AJ
Click to expand...
Since edges are two flat surfaces that meet, I don't see it as being unrelated. Obviously it is a phenomena that is observed.

A large carbide is of course as difficult to define as any other "large" thing. 20 micron+ carbides could probably be classified as large carbides. You're unlikely to notice individual missing carbides, the effect is noticed because carbides tend to cluster, and steels with large carbides tend to also have lots of carbides. You of course wouldn't be likely to observe carbide pullout without going to a fairly polished sharpening.

Here's the first micrograph I could find in my collection. I'll let you come up with your own analysis:

Uploaded with ImageShack.us
 
More micrographs! I hope everyone can't get enough of them. Here is showing how carbides effect the radius of an edge with cutting:

 
ajhuff said:
Hmmm.... kind of casually mentions it in passing. In the context of polishing a flat surface, not really the same as a knife edge.

Also, the context I have always read is the "large" carbides pulling out of the knife edge is the pull out is noticeable. How big is a "large" carbide? I still have my doubts.

What I'd like to see is some photomicrographs of a knife edge showing the missing carbides. Actually, I would love to see ANY photomicrographs of some knife edges, especially a transverse view. Are you aware of any Larrin?

Thanks,

-AJ
Click to expand...

If you are an avid knife user, you will notice after some use a knife will have some micro chipping which is carbide pull out, at the very least micro cracking that propagates from the carbides at the edge.

This is something that John Verhoeven ( former head of metalurgy at Iowa state) talks about.

Run your knife off the end of your thumbnail and you will get some feed back. Lastly, it's not wise to argue with Larrin.

Look at an edge under magnification and see what you learn.

Hoss
 
I was only asking questions not arguing. I greatly appreciate the feedback from Larrin.

-Aj
 
Larrin said:
More micrographs! I hope everyone can't get enough of them. Here is showing how carbides effect the radius of an edge with cutting:

Click to expand...

This top photo is of 12c27 and the bottom photo is of 440-C. Ofcourse the 12c27 has better edge stablility.

Hoss
 
I'm loving this stuff! Great images of what is actually going on.
 
Classic example of a picture speaks a thousand words! Those pics made it much easier to understand!
 
Larrin said:
Since edges are two flat surfaces that meet, I don't see it as being unrelated. Obviously it is a phenomena that is observed.

A large carbide is of course as difficult to define as any other "large" thing. 20 micron+ carbides could probably be classified as large carbides. You're unlikely to notice individual missing carbides, the effect is noticed because carbides tend to cluster, and steels with large carbides tend to also have lots of carbides. You of course wouldn't be likely to observe carbide pullout without going to a fairly polished sharpening.

Here's the first micrograph I could find in my collection. I'll let you come up with your own analysis:

Uploaded with ImageShack.us
Click to expand...

I assume that's a cross section of an edge. If so, it sucks to have that vein of rocks right down the middle. Also is that a lefty?
 
That's probably symmetrically sharpened and the photo is cut off at the bottom. The carbides down the middle is a good thing on a hunting knife, but you're right, not on a kitchen knife.

Hoss
 
Sharpenability

The relative ease or difficulty in sharpening a knife.

Several things affect sharpenability. The first is the thickness at the edge, the thinner the edge, the easier it will be to sharpen. There is simply less material to remove.

The size, volume, distribution, and hardness of carbides will affect how easy it is to sharpen. Some carbides, like vanadium carbides, are harder than some abrasives, like aluminum oxide. In such cases it would be necessary to use a harder abrassive to sharpen on to get the keenest edge. The smaller the carbides the easier it is to sharpen. The lower the volume of carbide, the easier it is to sharpen. The more even the distribution of the carbides, the easier it is to sharpen.

The manufacture of the steel has more affect on the carbides than does the forging or heat treating. Grain size to a lesser extent will affect sharpenability. Grain size can be controled by correct forging and heat treating. The smaller the grain the greater ease of sharpening.

Optimal hardness will increase sharpenability. Too hard and the edge will chip out in sharpening, too soft and the edge will roll, even in sharpening.

Burr formation and removal will affect sharpenability. This is controled by hardness and the amount of retained austenite. The elimination of retained austenite will greatly reduce the formation of a burr and will make it easier to remove on sharpening.

More to come.

Hoss
 
Stain resistance

the ability for a steel to resist staining, discoloring, rusting, or developing a patina.

Steel composition is the most important for this one. Chrome, nickel, and moly are the main alloying elements when added in sufficient quantities will make steels stainless. To make a steel that is considered stainless it needs to have at least 12% chrome and about 10 1/2% chrome in solution after heat treatment. Nickel in smaller amounts will help stain resistance. Moly actually helps steels against etching.

Heat treating is necessary in making martensitic stainless steels (the ones we make knives out of) fully stainless. In the annealed condition, steels have twice the carbide volume as in the heat treated condition. This is what happens to the carbon and chrome along with other elements in the matrix, it is put into the carbides so that there is very little in the matrix to make it hard. When the steel is heated a certain volume of carbide is desolved and it puts carbon and alloy into the matrix, and then frozen there allowing it to become hard and with enough chrome in the matrix it becomes stainless.

In general, the softer the stainless steel the less stain resistant it is.

The surface finish will also affect the stain resistance of a steel. The finer the finish, or the higher the polish, the more stain resistant it is.

Next we will rate some more popular steels on edge holding, toughness, sharpenability, edge stability, and stain resistance.

More to come.

Hoss
 
Thanks, Hoss. I was wondering about the stainlessness. This clears it up a lot for me.
 
Rating some stainless steels.

Steel type Edge holding Toughness Edge stability Sharpenability Stain resistance Overall rating
AEB-L...........6.................4..............10................10..................8.....................7.6
Stainless PM.8..................4..............7.5...............8...................8.5...................7.2
CPM 154.......7.5...............3..............6.5...............7...................8......................6.4
440-C...........7.5...............2..............4.5...............7...................8.5...................5.9
VG-10..........6..................3..............6..................7...................8.5...................6.1
19C27..........6.5...............3.5............6.5...............7...................7.5...................6.2

Some categeries may not be equaly important making the overall rating inaccurate. These numbers are based on our experiance in use and from charts from other researchers. I ran these steels by Larrin and averaged the numbers between us. Others may come up with slightly different numbers, but we feel that these should be close.

More to come.

Hoss
 
chart.jpg
 
Devin, can you name reference points for some of the categories? For example, it seems you have rated AEB-L as a 10 out of 10 for edge stability with others trailing so it is easy to see what the standard for comparison is. But for toughness it appears that all perform poorly? What is a knife material you would rate as a 10 to put these numbers in perspective? Same for edge holding? Or am I misunderstanding your rating system?

Thanks,

-AJ
 
Rating some carbon steels and tool steels

Steel type Edge holding Toughness Edge stabililty Sharpenability Stain resistance Overall rating
mystery
carbon.......8................4..............8.5.................8...................1.....................5.9
super wear
resistant....10..............3..............7....................6...................5.....................6.2
white.........5...............3..............8.5..................9...................1.....................5.3
blue super..8...............2..............5.....................7.5................2.....................4.9
O-1...........6...............3.5............8....................8.5.................1.5..................5.5
52100........7..............4.5.............9....................9...................2.....................6.3

Hoss
 
ajhuff said:
Devin, can you name reference points for some of the categories? For example, it seems you have rated AEB-L as a 10 out of 10 for edge stability with others trailing so it is easy to see what the standard for comparison is. But for toughness it appears that all perform poorly? What is a knife material you would rate as a 10 to put these numbers in perspective? Same for edge holding? Or am I misunderstanding your rating system?

Thanks,

-AJ
Click to expand...

Steels with a 10 rating in toughness would be ones with low hardness like austenitic stainless steels. Tool steels with high toughness would be like S-2 at an 8 and L-6 at a 6. Most tough tool steels have lower carbon levels along with low hardenability.

Edge holding is based on wear resistance. Steels like M-4 are a 9, most knife steels correctly heat treated rate at least a 5. Some of it is based on usable hardness.

Hoss
 
I have to say the pm and the mystery carbon are pretty nice to sharpen. I didn't think they were much different than 52100, to be honest. I think 440-C is too high, as well. That should be a 6. :)
 
Some of the numbers are theoretical and will be different in practice depending on skill level, equipment etc.

Thanks

Hoss
 
Thanks AJ for fixing my graphs

Hoss
 
It's fun and difficult coming up with the numbers. I've seen similar attempts on bladeforums and Blade Magazine and I always disagreed with the numbers. They're usually by knifemakers who don't know much about steel. At least when I disagree with my own numbers it's not off by 5 points.
 
Larrin said:
It's fun and difficult coming up with the numbers. I've seen similar attempts on bladeforums and Blade Magazine and I always disagreed with the numbers. They're usually by knifemakers who don't know much about steel. At least when I disagree with my own numbers it's not off by 5 points.
Click to expand...
I really like these ratings and I like the fact that stainless is separate, since the stain resistance gives stainless steels such a big edge (It looks like 440C is "better" than most carbon steels.).
 
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