Carbide size in knife steels

N

NjMS

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Feb 8, 2016
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Where can I find information or learn to interpret a steel data sheet regarding the carbide size in steel.*

For example I've noticed comment on say ZDP-189 / CPM M4 that it will sharpen well with a high grit edge as it has fine carbides.*

Yet say CPM S90V / S110V is better with a course edge due to the large carbides. (excuse my examples of they are incorrect but I hope you get the drift of what I mean) *

Is this carbide size directly related in some way to the steels composition on a chart etc.*
I'm always curious to understand these things better.

Sent from my D6503 using Tapatalk
 
Way too many variables as everything will and can change due to soo many different things one can do with the HT.

All the PM steels are fine grained... ;)
 
I have little knowledge on this subject but from what I've gathered, carbide size is a result of steel composition (alloy) and heat treat method.
For more information, I'll refer you to member Bluntcut.
Prepare for the rabbit hole/bottomless pit...
 
steel with carbides is similar to concrete, with the carbides being the aggregate, and the iron and carbon being the cement. The aggregate improves wear resistance.

Smaller carbides are usually better than large carbides for knife blades. Smaller carbides allow you to form a finer edge without the aggregate protruding. That's why PM alloys usually perform better as knife steels than non-PM steels. The PM process produces smaller carbides.

But, all carbides are not created equal. Some are harder than others.
For instance, iron carbide, such as cementite, is not that much harder than just steel. But Vanadium carbide is VERY much harder than steel.

Here is a chart of carbide hardnesses:
Carbidehardnesses.jpg


But there are more factors as well. When you start fooling with solid particles in a matrix, you have to worry about packing density of the particles. If all the particles are exactly the same size, they don't pack well and you don't get as good properties, compared to if you have multiple sizes.

I said all that to say, just looking at composition and carbide size isn't actually going to get you very far. The steel companies have teams of experts that fuss with these things and test out their theories. You and I aren't ever going to have as much knowledge about steel composition as they have.

What is a heck of a lot better is to look at something like Ankerson's cutting tests, or look at the wear resistance charts in the alloy tech data sheets. Far more useful.
 
NjMS said:
Where can I find information or learn to interpret a steel data sheet regarding the carbide size in steel.*

For example I've noticed comment on say ZDP-189 / CPM M4 that it will sharpen well with a high grit edge as it has fine carbides.*

Yet say CPM S90V / S110V is better with a course edge due to the large carbides. (excuse my examples of they are incorrect but I hope you get the drift of what I mean) *

Is this carbide size directly related in some way to the steels composition on a chart etc.*
I'm always curious to understand these things better.

Sent from my D6503 using Tapatalk
Click to expand...

Its not the size, Its the raw carbide volume

look up the steel chemistry here

http://www.zknives.com/knives/steels/steelchart.php


also sharpening understanding and abrasive selection

as Jim illustrates here

[youtube]K_R1yxULRuQ[/youtube]

and with some very in depth information here

https://scienceofsharp.wordpress.com/

BUT

This is what your looking for :D

"The carbides formed during the extremely rapid solidification are fine in size (2 to 4 microns), and are uniformly distributed throughout the microstructure. Compare this to the larger carbides (up to 50 microns or more in size),"


from here

http://www.crucible.com/eselector/general/generalpart1.html

heres more

Hardness of Carbides

Alloy elements (Cr, V, W, Mo) form hard carbide particles in tool steel microstructures.
The amount and type present influence the wear resistance.


• HARDENED STEEL • 60/65 HRC
• CHROMIUM CARBIDES • 66/68 HRC
• MOLYBDENUM CARBIDES • 72/77 HRC
• TUNGSTEN CARBIDES • 72/77 HRC
• VANADIUM CARBIDES • 82/84 HRC


Tool steels contain the element carbon, in levels from about 0.5% up to over 2%. The minimum level of about 0.5% is required to allow the steels to harden to the 60 HRC level during heat treating. The excess carbon above 0.5% plays little role in the hardening of the steels. Instead, it is intended to combine with other elements in the steel to form hard particles called carbides. Tool steels contain elements such as chromium, molybdenum, tungsten, and vanadium. These elements combine with the excess carbon to form chromium carbides, tungsten carbides, vanadium carbides, etc. These carbide particles are microscopic in size, and constitute from less than 5% to over 20% of the total volume of the microstructure of the steel. The actual hardness of individual carbide particles depends on their chemical composition. Chromium carbides are about 65/70 HRC, molybdenum and tungsten carbides are about 75 HRC, and vanadium carbides are 80/85 HRC.

These embedded carbide particles function like the cobblestones in a cobblestone street. They are harder than the steel matrix around them, and can help prevent the matrix from being worn away in service. The amount and type of carbide present in a particular grade of steel is largely responsible for differences in wear resistance. At similar hardnesses, steels with greater amounts of carbides or carbides of a higher hardness, will show better resistance to wear. This factor accounts for differences in wear resistance among, say, O1, A2, D2, and M4. Ideally, tool steels would contain as much carbide volume as needed for the desired wear performance. In fact “solid carbide” tooling is typically 85% or 90% tungsten carbide particles, in a matrix of 10% or 15% cobalt to hold them together. Chemically, the microscopic carbide particles in tool steels are similar to the carbide particles in solid carbide tools. However, very high amounts of carbide particles can lead to problems in grinding, or lower toughness. More comments on the effect of carbides on toughness and grindability are discussed in the following section: Effect of Steel Manufacturing on Properties.

Because of their high hardness, vanadium carbides are particularly beneficial for wear resistance. When present in significant amounts, vanadium carbides tend to dominate other types in affecting wear properties. For instance, M4 high speed steel’s chemical content is nearly identical to M2 high speed steel, except M4 contains 4% vanadium instead of 2%. Despite the high levels of molybdenum and tungsten carbides (about 6% tungsten, 5% molybdenum) in each grade, the small difference in vanadium content gives M4 nearly twice the wear life of M2 in many environments. In cold work tool steels, the carbide content in general, and to a limited extent the vanadium content in particular, may sometimes be used as a rough predictor of potential wear life.



great resource for understanding PM steel straight from the source




there is a ton of great information here on Bladeforums for you to absorb :D



Im forever in debt to this place for everything I've learned

:)
 
Thanks for the responses. I've more reading /learning and that's what is about.

Sent from my D6503 using Tapatalk
 
Do not confuse Grain size with Carbide size !!!

When Ht'ing take care of Carbide size first [get it small ] only then deal with Grain size [smaller is better here also ].

CPM steels [ PM steels ] are better .If you buy M4 make sure it CPM M4 !!

Vanadium = you'll see Niobium used in some steels now .The difference is that V likes grain boundaries [reduces grain growth ] while Nb likes a more uniform distribution.

Nitrogen - Acts somewhat like carbon but without the tendency of brittleness in higher amounts .
That's today's metallurgy lesson !!
 
There is a lot of info out there. CPM steels were developed in part to deal with relatively large amounts of carbides, that is to say a high volume percent. Many steels don't benefit from CPM processing/powder processing because they don't have enough carbide volume to need it. These tend to be simpler steels like 10xx, O1, A2, etc. Alloy content determines how much carbide there could be. Heat treatment and processing determine how much there is and how big they are.

Just as a teaser, it's rarely discussed in knife circles, but steel in the annealed condition has significantly more carbide volume than after it has been heat treated. The steel is generally too weak take advantage of that volume when annealed though.
 
Oh, and special thanks to mete for pointing out grain size and carbide size are distinctly different things and are dealt with separately in terms of processing.
 
Just to give some rough numbers, CPM steels have carbides in the 3 to 8 micron range, non-CPM steels with similar carbide volume, like D2 and 440C, have carbides in the 10 to 50 micron range, and the lower alloy steels like AEB-L, 52100, 1095, etc have carbides that are 1 - 2 microns and smaller. Steels like 5160, 1075, and some others don't have appreciable carbide volume normally.
 
How big are the carbides? Regardless of the steel, you'd need an electron microscope to see them.
 
The 50 micron (0.002") carbides are big enough to see with the naked eye, but on a polished surface they are difficult to see and difficult to tell what you're seeing.
 
In the steel making process you can sometimes get "massive carbides " in large sections which have always been a problem and were one of the driving forces to develop the CPM system These carbides are VERY large and easy to see.
For knives the sharpness [ minimum radius of the edge for that material] is better with smaller carbides . That means the large carbides of a D2 will never have a sharper edge than a powder steel!
 
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