Is Grain size of metal a BOGUS concept?

N

NeedItCheaper

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Jun 17, 2012
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So I have read many times that the smaller the grain structure of a metal determines how sharp it can get. Now every time I make a post about say VG10 or 154CM getting sharper than s30V or any other steel, people pop up saying "Oh no, I get it to cut air, yadda, yadda". It gets me thinking of this grain size argument. Is it a legit argument? Does a larger grain size actually stop a knife user from getting their knife sharper? Or is grain size so small for every metal out there, that no human being can actually utilize the sharpness?


Lots of questions, can anyone shed light on this issue? And if grain size is a legit comment to make, why don't knife manufactures list the grain size of the metal their knife is made of? Would seem to be a detail knife users would want to know, especially with proprietary steel.
 
to answer the second question first it is because they don't know the only way to tell would be to break it or a very skilled craftsman who watched it from start to Finnish they could guess but i dont know how many times they thermo cycle it.
and yes it is a very real concept that helps the steel hold an edge and bend better.
 
NO!

I am a material engineer and I will explain.

A metal as you know has an electron cloud, the main atom of iron is made into steel by carbon. The carbon is what diamond is. Carbides are ceramic molecules that are very hard in many cases such sappire cryrstal which is just aluminum oxide in clear state.

Grain size is the size of the carbides, they stick out like little teeth and also contribute too the properties of the steel.
Metal alloys like chrome are different they are part of metal matrix while vandium crystal or carbon crystals sit inbetween. Grain size refers too size, and time and temp determine the size.

A smaller size would wear faster in general but cut better while larger one might break or last longer or cut better.

it is very complex and science stops at testing, comes down too what you see as toughness, hardness or edge holding. Cooling or heat treat modifies both the metal and ceramic part. ceramic is an oxide or nitride in most cases. Born nitride is very hard.

By controlling impurties you can can contol seeding of crystals in the alloy, and the grain size of the metal. now there is size of the metal grains, what is around those grains.

Good knife blade is like soup, metal is the main broth, the small harding alloys are the little things in the soup! Well i tried too explain a complex subject and i been out of school for 30 years = also i am not a metalurgist - I am ceramic designer.

Under scope you see blobs not single piece of metal with things around the blobs - that is the grain. size is also important too the edge since if tip of the edge is one grain it is very difficult too break. The small the grain the sharper the edge in theory but it is very complex and I am not a metalurgist.

here is crystal of iron and photos of grains:

http://www.cashenblades.com/metallurgy.html
 
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Are you talking about grain size or carbide size? Some of the "super" steels have big ol fat carbides that are hard and increase edge holding but make it hard to get down to a super fine edge.
I can't remember who, but another member put it an interesting way. Imagine you are trying to form a triangle with as thin an edge as possible using modeling clay. One block of clay has BBs in it (small carbides), the other has marbles in it (large carbides), The third has ping pong balls in it (big ol carbides). Ever hear D2 referred to as having a toothy edge that won't get super sharp? ping pong balls.
 
per the above link:

"Martensite is the hardened phase of steel that is obtained by cooling Austenite fast enough to trap carbon atoms within the cubic iron matrix distorting it into a body centered tetragonal structure."

from about.com chemistry: "Vanadium is used in nuclear applications, for producing rust-resistant spring and high-speed tool steels, and as a carbide stabilizer in making steels. Approximately 80% of the vanadium that is produced is used as a steel additive or ferrovanadium"

as in Crucibles powder metal prosses - such as 30v which is very pouplar and new variants see crucibles site.

stainless: "Volume and Grain Boundary Diffusion of Chromium in Ni-Base Ni–Cr–Fe Alloys"

http://www.jim.or.jp/journal/e/pdf3/44/01/40.pdf

per the above article: "The incorporation ofchromium in iron- and nickel-base
alloys gives rise to two main advantages. It contributes
significantly to the solid solution strengthening and at the
same time, enhances the oxidation resistance. These alloys
usually contain some amount ofcarb on as well to further
enhance their load-bearing capacity. The advantages accruing
from the combined presence of chromium and carbon are
severely compromised ifthey react to form M23C6-type of
carbides. These carbides are mainly formed at the grain
boundaries and lead to the depletion ofthe chromium from
the matrix which decreases the strength as well as the heat
resistance capacity. Grain boundary precipitation also causes
the embrittlement ofthe alloy."

i hope that starts your journey too understand "the secret of steel" conan
 
oic0 said:
Are you talking about grain size or carbide size? Some of the "super" steels have big ol fat carbides that are hard and increase edge holding but make it hard to get down to a super fine edge.
I can't remember who, but another member put it an interesting way. Imagine you are trying to form a triangle with as thin an edge as possible using modeling clay. One block of clay has BBs in it (small carbides), the other has marbles in it (large carbides), The third has ping pong balls in it (big ol carbides). Ever hear D2 referred to as having a toothy edge that won't get super sharp? ping pong balls.
Click to expand...



best too look at photos of alloys that describe the structure of the metal and read general information above. grain is boundry is where the carbides and nitrides reside, the metal grain is surround by the electron cloud and unfied structure. The shape of the crystals and what is between or in is very complex in alloys.

clay anology is excellent. if the bb's are hard and they sit on the edge you have a great edge but it will break if there is too many bb's the clay woud crumble.

samuri swords, are different - they have two sturctures, grain size and/or crystal type one too bend and hold the sharper more brittle crystal. two different structures from the same metal alloy from straw and iron. remember the history steel is the inpurties in the iron make the steel - famous woot steel - research it.
 
Forging - all steel is forged. this is how grain is made, this is steel is mixed and impurties are driven out and boundries unified.

rolling is forging, with out forging you have inconsitent matrix which would not doubt fail where the metal has not been formed into proper grain. research this too. but this is why the samuri swords where folded, work in carbon too work out impurties and develope consistent grain.
powder steel is reduce = forging.

do not confused a single forging for a steel blank, forging is large worked peice of metal.

i just want too add that - good luck
 
I'm no engineer but I can sharpen and will agree that grain size has no translation to sharpness.

Material hardness and the angle you sharpen at will determine sharpness.
 
It is not a bogus concept. The finer the structure of a knife steel the finer edge one can achieve.

Knife Edge Diagram PDF

Click Here

Done by R. Landes, a metallurgist and knife maker.

Experiments on knife sharpening:

Click here

Done by metallurgist J.D Verhoeven.

Note the edges are 0.5 Micron. If any structure of a knife steel is bigger then that and one cannot sharpen it or it chips out then you wont be able to get a quality razor edge. That is why razors still use steels that are fine in structure. Bohler developed AEB-L for Gillette to my knowledge. Similar steel is 13C26.

Click to download pdf of Bohler

Sandvik:

Razor edge sharpness

Sandvik 13C26 knife steel is developed for razor blade applications which means a strong focus on hardness, sharpness and edge stability.

Sandvik 13C26 is the Sandvik knife steel grade with the highest achievable hardness while still maintaining the fine carbide structure which is characteristic for Sandvik's knife steels.

With exceptional edge performance and good toughness this grade is an excellent choice for demanding cutting applications where the moderate corrosion resistance of Sandvik 13C26 knife steel is not a key issue, or if the blade is coated for corrosion protection.

With a recommended hardness range of 55-62 HRC, exceptional edge performace with scary sharpness and good toughness, Sandvik 13C26 knife steel is recommended for surgical blades, razor applications, whittling or as a surface coated EDC (Every Day Carry) knife.

Like most of Sandvik's knife steels this grade is fineblankable enabling efficient production.

SANDVIK source link

Unfortunately, many of these steels have had some bad rep due to improper heat treat resulting in poor performance.

Here is a test of AEB-L edge retention and how easy it can be restored to shaving sharpness:

[video=youtube;6B4QH7DJvVE]http://www.youtube.com/watch?v=6B4QH7DJvVE[/video]

These steels however are not as wear resistant as others and currently, most people like their high wear resistant steels like M390, S90V, 10V etc.

Here are initial tests done by Phil Wilson.

http://www.bladeforums.com/forums/showthread.php/424485-AEB-L-Cutting-tests-and-first-impressions

and Jim Ankerson

http://www.bladeforums.com/forums/s...based-on-Edge-Retention-cutting-5-8-quot-rope

Showing the performance of higher wear resistant steels in rope cutting.
 
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i TRY AGAIN:

grain size and grain boundry are important to all aspect of a metal for any use that requires, extreme properties of such metal.

impurties in japaneese steel made them rust in the 70's it was sulfer that is why the desulfer iron.
grain size would affect the edge, the strenght, the flex, the fatigue., toughness, corrosion... o heck i give up!


lets take crossion fine grain would be more prone to corrosion since there is more surface area.

surface area is very important iin relation too the grain size. remember if something is one tenth the its volume is is cubed too or 1/1000 but if it is 1/100 it surface are its volume is 1/1,000,000

THE RATIO

the 1/100 grain has massive surface area compared too the 1/10 size grain. This is where physics gets weird, remember the metal is an electron cloud, if the boundry is ceramic ... nitride or cribide then the cloud on the surface is much greater in proportion too the grain volume. ceramics on the boundry do not have an electron cloud. electons are locked in the atoms, molecules or crystals.

now are you confused!

the cloud protects the metal since elctrons can move around, large cloud and small grain would have much different properties due too the volume to surface area alone.
 
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