I am starting to think cutting is more in the geometry than in the apex...

Big Chris,

Thank you. You mean the Z wear was zero ground (what is the initial angle?) and tested by adding 24 inclusive bevel bit by bit until it is stable? :confused:

Working out calculation, 0.006" - 0.008" is about 0.15mm - 0.2mm, which is 150-200 micron. Some stats I read has carbides size varies around 5 - 20 micron, depending on steel & heat treat. With 30 inclusive (easier to calculate), it works out about 350 micron edge height (if thickness is 200 micron). Within this 200 micron base with 350 micron tall, the matrix surrounding 5 - 20 micron carbides that's not too dense should suffice to hold them stable.

I have to re-look data to check how much carbide in volume just to satisfy my curiosity.

Come to think about it, most production knives are way too thick!
 
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The common, respectable knife steels where you'll have the most problems with large carbides are 440C and D2. They will give you excellent wear resistance, but they are not very tough.

The pure carbon steels, such as 1095, can have very fine carbides, so they can be tough with excellent edge stability. But their wear resistance is usually not very good.

Power steels, which are often referred to as super steels, can offer fine grain and reasonably fine carbides, so they can be middling tough and have good edge stability. They can get quite a bit sharper than the coarse carbide steels, and they can absolutely shine when it comes to wear resistance.


http://www.smt.sandvik.com/en-us/pr.../knife-steel-knowledge/different-steel-types/
 
Any idea what the grain size of the powder steels is?

Twindog said:
The common, respectable knife steels where you'll have the most problems with large carbides are 440C and D2. They will give you excellent wear resistance, but they are not very tough.

The pure carbon steels, such as 1095, can have very fine carbides, so they can be tough with excellent edge stability. But their wear resistance is usually not very good.

Power steels, which are often referred to as super steels, can offer fine grain and reasonably fine carbides, so they can be middling tough and have good edge stability. They can get quite a bit sharper than the coarse carbide steels, and they can absolutely shine when it comes to wear resistance.


http://www.smt.sandvik.com/en-us/pr.../knife-steel-knowledge/different-steel-types/
Click to expand...
 
me2 said:
Any idea what the grain size of the powder steels is?
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Grain size can vary a lot, and I’ve never been able to find a good summary of all knife steels. And even within just the powder steels, there is quite a variation. Third-generation powder steels are marketed as having finer grain structure than first- and second-generation powders, as well as having smaller carbides and a cleaner microstructure relatively free of inclusions.

In addition, the heat treating process can affect grain size a lot. Thermal cycling between steel phases can reduce grain size, while over-heating can increase grain size. Two knifemakers, each buying S90V from the same steel manufacturer, can produce knife blades with very different grain sizes in the steel.

Ordinary D2 runs grain size of about 10-15 microns, often much higher. CPM D2 (powder D2) reduces grain size to about 5 microns. Bluntcut has said that M390 has grain size of 1-2 microns. Maybe he’ll pop into this discussion.The OP was surprised that thinner geometry cuts so much more effectively. That geometry is limited by steel science. Edge stability (toughness and strength) is affected negatively by not just by coarse grain size, but also by large carbide volume and size; so a lot of people are concerned that the high-alloy super steels are not suited to acute edges and thin geometry because of their large carbide volumes. There is truth to those concerns, however, with advanced powder steel technology, grain size can be reduced, carbide size can be reduced and made more uniform in distribution and the steel can be cleaner, although as you have noted, ingot steel can be made clean too.

Overall, these advantages in the production of powder steel can offset to a large degree the disadvantages in strength and toughness associated with higher carbide volume, allowing more aggressive blade and edge geometry, while leaving untouched the high-alloy steels’ incredible advantages in edge wear resistance.
 
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The reason I ask is that many people say that the powder steels have very fine grain, but no one is ever sure of the size. The micrographs I've seen point to sizes in the 35 micron range, which is smaller than the powder size. The carbide size is in the range of 3-6 microns or so, but the volumes are very high, 15% and up. Carbide sizes in low alloy steels are measured in decimals of a micron. Standard HT procedures for 52100 produce carbide sizes in the range of 0.2 microns with grain sizes of 5 to 11 microns. I would be interested to read Bluntcuts material on M390 grain size. His estimates of grain size in past postings has been somewhat questionable. I would also be interested as to the procedure for reducing D2 grain size, as the material I've seen has it somewhat larger, even in CPM form. The carbides are much reduced, but the grains are again in the 30-40 micron range.

The highly alloyed steels, like the powder steels, are resistant to grain size changes to a much greater degree than low alloy steels. This is partly by design, as the grain size would grow very rapidly at the austenization temperatures used. The finest powder sizes I've seen are around 150 microns, which is much bigger than the grains themselves. This resistance to change applies to refining efforts as well as growth issues, though shrinking is easier than growing. Even conventionally produced high speed steels can get down to 4-8 microns in grain size with proper processing, but in some cases one can get melting before the grain size is blown (enlarged to the point of ruination).

Very sharp edges, honed on something like an 8000 grit water stone, are only about 0.5 microns wide. Given the carbide size of even the best powder steels today is on the order of 4x as big, I can see where the concerns of edge stability are coming from. Also, keep in mind, the grain, carbide, and powder sizes mentioned are average sizes. In any given picture one can find both smaller and larger grains, carbides, and powder particles.
 
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Yes, I have trouble finding reliable information. Easy to find contradictory information. I think the nozzle size for creating powder steel limits the grain size. There is no question that the simple carbon steels can be very fine grained, leading to excellent edge stability and the ability to create a super fine edge.

Ed Fowler calls 52100 an "honest steel," meaning it responds well to proper heat treating. 52100 can be awesome, but I can't afford one of Ed's knives.

I suspect that sharpening techniques are more critical for powder steels. My sense is that fine diamond steels that can evenly abrade both the carbides and the steel matrix are critical, but I see a lot of excellent sharpeners here who disagree.
 
Just to avoid confusion, by "standard treatment" I wasn't referring to Ed's treatment of 52100. I meant standard industrial treatments for bearings and razor blades (odd combo huh?) and such. I have not been a fan of diamond sharpeners, though I may have to change to them for final honing. Some reliable work has been done with a DMT Coarse as the finishing grit.
 
This is timely for me because I recently bought Murray Carter's Blade Sharpening Fundamentals digital download. He emphasizes early on that blade *thinning* is necessary in just about any knife and that we should all assume that every knife needs to be thinned. He's talking about grinding the secondary bevel (not the cutting bevel) to make the overall shape thinner. He also says this should be done with EVERY sharpening to maintain the same overall geometry throughout the life of the blade.

I wonder how many people here *ever* thin blades? I know I never have. Note: I am NOT talking about reprofiling the primary (cutting) bevel. I'm talking about flat grinding the side of the blade to make it thinner overall. For most knife enthusiasts I know this would be nearly unthinkable, as it would scratch the sides and maybe damage or remove the maker's stamp.

I need to start experimenting with this on my junk blades and see how it works for me. Seems like it's mostly about rounding the shoulders of the secondary to primary transition. That is, until you spend TONS of grinding time to actually remove significant stock from the blade itself.

Just some thoughts. Sometimes I feel like I'm just getting started with sharpening. :)

Brian.
 
bgentry said:
This is timely for me because I recently bought Murray Carter's Blade Sharpening Fundamentals digital download. He emphasizes early on that blade *thinning* is necessary in just about any knife and that we should all assume that every knife needs to be thinned. He's talking about grinding the secondary bevel (not the cutting bevel) to make the overall shape thinner. He also says this should be done with EVERY sharpening to maintain the same overall geometry throughout the life of the blade.

I wonder how many people here *ever* thin blades? I know I never have. Note: I am NOT talking about reprofiling the primary (cutting) bevel. I'm talking about flat grinding the side of the blade to make it thinner overall. For most knife enthusiasts I know this would be nearly unthinkable, as it would scratch the sides and maybe damage or remove the maker's stamp.

I need to start experimenting with this on my junk blades and see how it works for me. Seems like it's mostly about rounding the shoulders of the secondary to primary transition. That is, until you spend TONS of grinding time to actually remove significant stock from the blade itself.

Just some thoughts. Sometimes I feel like I'm just getting started with sharpening. :)

Brian.
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I do sharpen/regrind/thin out the primary bevel all the time Brian! I love the haziness of waterstone sharpened knives on the blade, this makes the knife more mine! I don't collect knives, I have them to use them (as much as I can - my job unfortunately does not involve a knife at all !!). Just for the kicks - take a kitchen knife and lay it flat on a freshly flattened stone then thin it out. You will see how uneven even the flat can be. If you thin out the blade properly and (on a "v"-edge) smooth out the shoulder a bit and you have a slicer, even if it is not shaving sharp.
 
bgentry said:
This is timely for me because I recently bought Murray Carter's Blade Sharpening Fundamentals digital download. He emphasizes early on that blade *thinning* is necessary in just about any knife and that we should all assume that every knife needs to be thinned. He's talking about grinding the secondary bevel (not the cutting bevel) to make the overall shape thinner. He also says this should be done with EVERY sharpening to maintain the same overall geometry throughout the life of the blade.

I wonder how many people here *ever* thin blades? I know I never have. Note: I am NOT talking about reprofiling the primary (cutting) bevel. I'm talking about flat grinding the side of the blade to make it thinner overall. For most knife enthusiasts I know this would be nearly unthinkable, as it would scratch the sides and maybe damage or remove the maker's stamp.

I need to start experimenting with this on my junk blades and see how it works for me. Seems like it's mostly about rounding the shoulders of the secondary to primary transition. That is, until you spend TONS of grinding time to actually remove significant stock from the blade itself.

Just some thoughts. Sometimes I feel like I'm just getting started with sharpening. :)

Brian.
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If its a regular blade pattern, I do it every time I touch up the edge. If its a hollowground I don't bother, and on some of my Kitchen knives that are of very thin stock I don't bother - likewise my machetes. If the secondary (back bevel) has any meat to it, I thin it out. I'll even thin out the back bevel on Scandis.

Have had a couple of knives I wouldn't even use until I had thinned them out.

Sharpen the whole blade whenever applicable, it can make a huge difference.

As with Andy, I also find it a fun challenge to see how nice I can get the finish by hand while I thin it out.
 
bgentry said:
This is timely for me because I recently bought Murray Carter's Blade Sharpening Fundamentals digital download. He emphasizes early on that blade *thinning* is necessary in just about any knife and that we should all assume that every knife needs to be thinned. He's talking about grinding the secondary bevel (not the cutting bevel) to make the overall shape thinner. He also says this should be done with EVERY sharpening to maintain the same overall geometry throughout the life of the blade.

I wonder how many people here *ever* thin blades? I know I never have. Note: I am NOT talking about reprofiling the primary (cutting) bevel. I'm talking about flat grinding the side of the blade to make it thinner overall. For most knife enthusiasts I know this would be nearly unthinkable, as it would scratch the sides and maybe damage or remove the maker's stamp.

I need to start experimenting with this on my junk blades and see how it works for me. Seems like it's mostly about rounding the shoulders of the secondary to primary transition. That is, until you spend TONS of grinding time to actually remove significant stock from the blade itself.

Just some thoughts. Sometimes I feel like I'm just getting started with sharpening. :)

Brian.
Click to expand...

This is one point I was trying to make at the start of the thread. People don't seem to do much blade thinning around here even though mostknife nuts know it improves performance. I know there are people on here who do thin their blades but it doesn't get discussed.
 
bgentry said:
This is timely for me because I recently bought Murray Carter's Blade Sharpening Fundamentals digital download. He emphasizes early on that blade *thinning* is necessary in just about any knife and that we should all assume that every knife needs to be thinned. He's talking about grinding the secondary bevel (not the cutting bevel) to make the overall shape thinner. He also says this should be done with EVERY sharpening to maintain the same overall geometry throughout the life of the blade.

I wonder how many people here *ever* thin blades? I know I never have. Note: I am NOT talking about reprofiling the primary (cutting) bevel. I'm talking about flat grinding the side of the blade to make it thinner overall. For most knife enthusiasts I know this would be nearly unthinkable, as it would scratch the sides and maybe damage or remove the maker's stamp.

I need to start experimenting with this on my junk blades and see how it works for me. Seems like it's mostly about rounding the shoulders of the secondary to primary transition. That is, until you spend TONS of grinding time to actually remove significant stock from the blade itself.

Just some thoughts. Sometimes I feel like I'm just getting started with sharpening. :)

Brian.
Click to expand...

That's how I usually 'thin' my blades. Unless the blade is severely THICK, most of the discernable benefit can be attained by gradually taking down the shoulders, and taking a little more off each time you sharpen up the blade. Over time, the shoulders themselves will diminish, and the blade starts looking more like a zero-grind. This can even be done in stropping, using compounds that are a little more aggressive, on very firm or hard backing. I've been doing some of this in the last day or two, with a large Case Sod Buster (2138 SS; flat grind, 0.10" spine thickness). Started by thinning down the shoulders on a Fallkniven DC4's diamond side (25µ), and then stropping on denim over wood (Home Depot 18" paint-stirring stick), with some Sears #2 grey AlOx compound. The stropping puts a near-mirror on the convexed shoulders & edge, and I can already see the polish 'moving up' the side of the primary grind with additional stropping. In simple paper-slicing tests, it's slicing as effortlessly as my Sod Buster Jr. (2137 SS; thinner blade @ ~0.08" spine thickness, and hollow-ground), and I'd already given it the same treatment some time ago. Both have proven to be great tomato-slicers, after giving them this treatment. :thumbup:


David
 
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Yes, geometry cuts. Steel holds the geometry in place. Wear resistance helps to prevent the erosion of the steel caused by frictional forces acting against the steel while in use.
 
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