Carbide Volume, edge stability, edge angles, and performance

[PocketZen]

Hello All,
I have never started a thread on this forum but have just gotten very interested in the concept of carbide volume and how it effects performance. Really just love the :spyder: Forum because it is packed full of info with a great internal culture; a mutual desire to learn and share knowledge.
Personally I have grown to enjoy acute, low inclusive angle edges. Previously I understood hardness was a major factor in a steels ability to tolerate and hold such edges. However after reading the discussions here, Cliff frequently cites carbide volume as a significant factor in edge stability as well. Now I have several question:
1) How do I calculate or obtain the carbide volume of a steel?
2) Can we can categorize steels on a continuum from low carbide, medium, high, considering the number of steels available today?
3) AEB-L is frequently cited as having low carbide volume what are other examples of low carbide steels?

Thank you all in advanced for sharing your knowledge and experience.

[Clip]

You'll have to look at microstructures to know for sure. This involves mounting and polishing samples as close or closer than the .3 micron level, then etching the surface with an acid solution containing nitric, hydrochloric or picric acid. After that, take a look at it on a microscope and you'll be able to see individual carbides.

I suppose you could categorize steels from low to high carbide content, but you'll also have to categorize according to which carbides are present.

Usually low carbide steels have a low carbon content. Without the carbon, other elements like vanadium, tungsten, niobium and chromium can't form carbides.

If someone can get some of the blade hole cutouts I might be able to take a look at them and get pictures of the carbides.

[Cliff Stamp]

1) How do I calculate or obtain the carbide volume of a steel?

It can be calculated through Thermo-Calc and similar or obtained from the manufacturer directly, or calculated from the equations which correlate carbide volume to alloy content (these are often in the patent data).

2) Can we can categorize steels on a continuum from low carbide, medium, high, considering the number of steels available today?

Yes, this is done by the way for all steels, you just have to look up the materials data, see ASM for example.

3) AEB-L is frequently cited as having low carbide volume what are other examples of low carbide steels?

All the plain carbon steels and low alloy steels like 52100, 5160. All of the stainless similar to AEB-L (carbon/chromium ratio). If you look at the isothermals you can estimate carbide fraction from the distance from the carbon saturation line. AEB-L for example is on it when austenized at 1100 C so would have no primary carbides upon full soak/solution.

[PocketZen]

Thanks Chris. I really am enjoying your Pics!

[PocketZen]

It can be calculated through Thermo-Calc and similar or obtained from the manufacturer directly, or calculated from the equations which correlate carbide volume to alloy content (these are often in the patent data).



Yes, this is done by the way for all steels, you just have to look up the materials data, see ASM for example.




All the plain carbon steels and low alloy steels like 52100, 5160. All of the stainless similar to AEB-L (carbon/chromium ratio). If you look at the isothermals you can estimate carbide fraction from the distance from the carbon saturation line. AEB-L for example is on it when austenized at 1100 C so would have no primary carbides upon full soak/solution.

Thank you Cliff. I really appreciate you helping me understand this concept. So I don't have access to Thermo-Cal, and the ASM website seems to also require a subscription. You mentioned a formula, can you share it?
Typically I only am able to access a steels composition through the manufactures website. For example: http://www.crucible.com/eselector/prodb ... pm3vt.html

Now forgive me here if I am totally misunderstanding the concept. From what I am understanding CPM 3V would have less carbide volume than A2, O1, Cru-Wear, D2, M4 etc, however a greater number of carbides than 8670, 15n20, 1084...

[Cliff Stamp]

You mentioned a formula, can you share it?

They are typically in the patent files, though I have seen them in ASM and other standard references. It usually can be estimate just grossly from the wear resistance, though different carbide types can skew this, vanadium and tungsten for example can provide high wear at low volumes due to hardness.

From what I am understanding CPM 3V would have less carbide volume than A2, O1, Cru-Wear, D2, M4 etc, however a greater number of carbides than 8670, 15n20, 1084...

The carbide content of O1 is high yes, but typically you can ignore pure cementite as it is sub-micron in size and will not impact edge stability in a negative manner, in fact if anything it slightly increases it.

[PocketZen]

Code: Select all

Ok found that Patent data you were talking about.
[ATTACH]19963[/ATTACH]
Very interesting!

[Cliff Stamp]

Very interesting!

Note that the metal/metal wear tests are nonlinear in response and thus you can generate any data you want showing the extent of benefit of high wear steels by picking the appropriate stopping point (and adjusting the grinding speed). It isn't as if in use you would notice 10V having that kind of extreme benefit over D2 in a knife unless you used it to the point where the edge was essentially no different than the spine. But, it is useful to note the influence of both carbide volume and in particular high hardness carbide content on wear resistance, just on a qualitative level.