What makes a steel easy to sharpen?

DeadboxHero

DeadboxHero

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If all things are equal ( thickness, grind, hardness, sharpening techniques and abrasives used) what allows a steel to take an edge better then others?
 
Grain structure and carbide size me thinks
 
What's a simple way to explain grain structure and carbides that won't blow my mind? I bought a material science book but its not specific or simple enough for me to understand.
 
Heat treat plays an important part along with carbides/grain structure. Given the same steel, a higher HT will be more difficult to sharpen.
 
Your skill level at how to sharpen steel.

That, above all else, will determine whether it's easy or hard to sharpen any steel used on a knife....

All steels can take a very fine edge with the proper technique and stones.
 
DeadboxHero said:
What's a simple way to explain grain structure and carbides that won't blow my mind? I bought a material science book but its not specific or simple enough for me to understand.
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Grain structure is the key, if material hardness and sharpening technique are held equal. Here is a site that explains it pretty simply: http://www.the-warren.org/ALevelRevision/engineering/grainstructure.htm

Metals have a crystalline structure ... When a metal solidifies from the molten state, millions of tiny crystals start to grow ... These crystals form the grains in the solid metal ... Each grain is a distinct crystal with its own orientation.
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When you heat steel above 723 C, it forms a crystalline structure known as austenite that is quite tough but not particularly strong. When you cool the steel, you alter this crystalline structure in different ways depending on the rate of cooling. The final crystalline structure may be very hard but very brittle, very tough but relatively soft, or a mixture of the two. The harder and more brittle the structure, the harder and sharper your abrasives need to be to shape it appropriately, but the finer the edge. The softer the material, the easier it is to shape, but it may not hold that shape very well. If the structure is very brittle in some large areas, and very soft in others, then it will be frustrating to work with. A uniform distribution of very fine, strong, interlocking grains (martensite) will maximize toughness and hardness, allowing for a finer edge (though not the finest) to be more easily achieved.

After that, it is a matter of carbide content - size and distribution and total volume. Carbides are crystals embedded in the steel matrix, and the same rules apply - harder, larger carbide aggregates take a finer edge but are more difficult to shape and tend to fracture out of the matrix; softer carbides are easier to shape but more prone to wear; smaller carbide aggregates are less prone to fracture out of the matrix (having more matrix to hold them in) so are much easier to work with (tougher, less brittle steel) but produce a less fine edge than what larger carbide-aggregates are capable of.

You balance brittle hardness with ductile toughness through altering grain structure via steel composition and HT protocol to achieve the best edge for the task at hand. That edge may not be the finest achievable, but that might be too weak and brittle; it might not be the toughest, but tougher might not be strong enough.
 
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DeadboxHero said:
Great info, so its grain size?
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Grain size is only part of it, the crystalline structure of those grains is key. Large carbide aggregates can be difficult to sharpen even though they'll take a finer edge, most users accidentally fracture them out of the matrix instead. Smaller carbide aggregates are less prone to fracture out and do less damage to the edge when they do, but they do not allow for as fine of an edge. Most of the time, that doesn't matter, we don't need edges that fine and what they achieve is PLENTY sharp for our uses. The same goes for the steel matrix itself. Martensite isn't as hard as carbide, can't form as fine of an edge, but the edge it can form is usually PLENTY sharp for our uses. By mixing very small and hard carbides amidst relatively tough martensite, we accomplish a sufficiently strong, tough, wear-resistant edge that is easier to shape in the first place. If we want a more wear-resistant edge, we use more or larger carbides. If we want to make a stronger, tougher edge, we use less or finer carbides.
 
RevDevil said:
It's a combination of your skill as a sharpener (or lack of), the steel itself (carbide volume, grain structure, etc), hardness of said steel, and the media you are trying to sharpen with.
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said much more eloquently than I. :thumbup:
 
All things equal, skill, hardness, heat treatment, etc what makes a steel thats easy to sharpen to a razor for instance super blue vs something more difficult like 440a? Same angles, geometry, abrasives, skill.
 
DeadboxHero said:
All things equal, skill, hardness, heat treatment, etc what makes a steel thats easy to sharpen to a razor for instance super blue vs something more difficult like 440a? Same angles, geometry, abrasives, skill.
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Again, this is one of those trick questions that has no right answer and I might be way off in my attempt but here it goes. The thing is there is no "same" skill, it's something that develops over time. Some people can sharpen and some can't. I would say in this example since 440A and Super Blue are on opposite ends of the spectrum, the trade off between the two are kind of huge. One being classified as stainless and the other not, there is also the high refinement in one and not much in the other. High Vanadium in one helps form carbides, but does more for stain resistance. Super Blue is considered "exotic" and may have some properties that your 440A does not. There is no "all things being equal" because there is always a trade off.
This reminds me of trying to explain what a certain food tastes like to someone that has never had it. If this question had a single correct answer, foundries and the cutlery industry would no longer have to do research or testing.
 
RevDevil said:
Again, this is one of those trick questions that has no right answer and I might be way off in my attempt but here it goes. The thing is there is no "same" skill, it's something that develops over time. Some people can sharpen and some can't. I would say in this example since 440A and Super Blue are on opposite ends of the spectrum, the trade off between the two are kind of huge. One being classified as stainless and the other not, there is also the high refinement in one and not much in the other. High Vanadium in one helps form carbides, but does more for stain resistance. Super Blue is considered "exotic" and may have some properties that your 440A does not. There is no "all things being equal" because there is always a trade off.
This reminds me of trying to explain what a certain food tastes like to someone that has never had it. If this question had a single correct answer, foundries and the cutlery industry would no longer have to do research or testing.
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Huh? I don't understand, simple observations show some steels sharpen quicker and better then others. What metallurgical properties make that happen? Is it carbide volume? Grain size?
 
Of course but if they have the same hrc but different alloys how do those alloys form structures that shape edges faster then others?
 
Beside properties of steel itself, thickness of the edge plays big role on ease of sharpening.
 
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