Oil stones and diamond vs vanadium carbides

thanks for the input everyone... if it's not the size of the carbides or carbides being stripped away during sharpening, what factors cause s30v (or others like s90v) to lose the initial sharpness quickly?
 
Sandvik does not use PM. Their steels have sub-micron carbides due to the balance of alloying. 19C27 is a different animal that they created specifically to create larger carbides.
The carbides are the white areas in those images. The grains are larger than the carbides in the PM steel. Fine-grained steel still has grains 10 microns in diameter, grain size does not influence the radius of a sharpened edge.
All steels lose initial sharpness quickly. The abrasive wear and plastic deformation against the edge where the pressure is immense will cause a very rapid increase in the radius of the cutting edge. As the edge radius increases, the pressure and rate of wear decreases relative to the force applied.
 
hardheart said:
Sandvik does not use PM. Their steels have sub-micron carbides due to the balance of alloying. 19C27 is a different animal that they created specifically to create larger carbides.
The carbides are the white areas in those images. The grains are larger than the carbides in the PM steel. Fine-grained steel still has grains 10 microns in diameter, grain size does not influence the radius of a sharpened edge.
All steels lose initial sharpness quickly. The abrasive wear and plastic deformation against the edge where the pressure is immense will cause a very rapid increase in the radius of the cutting edge. As the edge radius increases, the pressure and rate of wear decreases relative to the force applied.
Click to expand...

i'm looking for the reason these higher vanadium content steels lose the initial sharpness faster than others like 154cm or even 440c. i was under the impression the black spots were the carbides? it looks like the micrographs of 154cm and d2 etc at the same magnification have large quantities of the white areas. considering the small size of all the particles of cpm steels it's hard to say anything definitive about volume by eyeballing it, but it seems like more than .4-1.0 by content on 154cm or d2.
 
154CM and D2 have lots of chromium carbides. S30V is 14.5% carbide, 154CM is 17.5%, and D2 is 15% (though this can change based on heat treat). I do not have specific numbers on how quickly each steel loses initial sharpness, it is highly dependent on edge geometry and heat treat. But the edges would first have to be in the same condition before an assessment of sharpness decrease could be compared.
 
You are posing a misunderstood question.

The best answer one could give to your question is: That's just how the steel performs. High vanadium steels don't rely on the starting sharpness for the majority of its edge retention.
 
knifenut1013 said:
You are posing a misunderstood question.

The best answer one could give to your question is: That's just how the steel performs. High vanadium steels don't rely on the starting sharpness for the majority of its edge retention.
Click to expand...


People can prove that to themselves very quickly and easy also buy taking a steels like 1095 and say S30V, Polish both edges the same then start cutting abrasive materials like rope or cardboard.

I say polished edges because that will speed up the process of dulling so one won't have to do as much work to see the results.

They will find that the lower alloy steel (1095) will be dull as a butter knife while the higher alloy steel (S30V) will still be cutting long after.

That is if they really want to be honest with themselves and find the truth, it can be a simple test using the same media for both knives.

Comparing those two steels one doesn't really need to be super accurate because of the large difference in those two steels edge retention wise as long as they are close to the same thickness and the edge geometry and thickness is close.

Rope is the better test medium because it will show dullness faster as in the blades will start to slice instead of bite when making slicing cuts so it will really show up.
 
hardheart said:
Sandvik does not use PM. Their steels have sub-micron carbides due to the balance of alloying. 19C27 is a different animal that they created specifically to create larger carbides.
The carbides are the white areas in those images. The grains are larger than the carbides in the PM steel. Fine-grained steel still has grains 10 microns in diameter, grain size does not influence the radius of a sharpened edge.
All steels lose initial sharpness quickly. The abrasive wear and plastic deformation against the edge where the pressure is immense will cause a very rapid increase in the radius of the cutting edge. As the edge radius increases, the pressure and rate of wear decreases relative to the force applied.
Click to expand...
On the one hand, I seem to have really stepped into something messy here. On the other hand, I'm still learning something new in all this.

Sandvik does have a powder metals operation (links below). But, until you mentioned it, I hadn't realized they (apparently) aren't using it for their knife steels, at least not yet. They do produce powders for 'tool steels' and others like D2 and 440C, however. Looking a little more into this, Sandvik's process for their blade steels is regarded as extremely clean (minimal impurities), which seems to account for the reputation for edge fineness in their blade steels.

http://www.smt.sandvik.com/en/products/metal-powder/list-of-materials/

http://www.smt.sandvik.com/en/products/metal-powder/list-of-materials/tool-steels/

http://www.smt.sandvik.com/en/products/metal-powder/list-of-materials/martensitic-stainless-steels/
 
They probably won't be using those powders for PM alloys. Producing the powder is part of the PM process, but it goes into hot isostatic pressing. That would be a substantial investment, and their cutlery steel alloys would gain nothing from the process. Good links though for anyone into laser sintering (wish I could afford the equipment)
 
i would know that relative or even absolute hardness does not form an inflexible heirarchy when it comes to blade steel and sharpening medium. the best example is diamond used to cut or polish diamond. one plays on the pecentage of diamond grains in the abrasive medium that's oriented so that their strongest points are bearing down on the work's points of weaknesses (dictated by the mineral's crystal structure and cleavage pattern.)

similarly, a somewhat softer medium like corundum or moissanite can be used to polish vanadium carbide. and this, assuming whole crystals. if the carbide bits are fine and embedded in a softer matrix, even easier.
 
knifenut1013 said:
You are posing a misunderstood question.

The best answer one could give to your question is: That's just how the steel performs. High vanadium steels don't rely on the starting sharpness for the majority of its edge retention.
Click to expand...

so basically the why of it is something people either just don't know or care about? my whole thing was noticing that's the way they perform, and hoping to find out it was due to some variable i could adjust rather than an unknown inherent quality.

anyway, i think i've about milked this dry, thanks for the responses everyone.
 
You must log in or register to reply here.
Back
Top