Recommendation? What makes a knife harder to sharpen?

[Bo-dacious]

Hey guys, I've heard about knife steels like s90v or cpm 10v that are a lot harder to sharpen than say 420 or 440 for random example. What makes a steel harder to sharpen? Like does it take more strokes to get a burr? Or does it actually take more skill to sharpen it? What should I do differently to sharpen a knife with this kind of steel on say an edge pro?

Thanks,

Bo

 

[Blues]

Read this, especially the beginning part for some concise info.

When you start getting into the wear resistant high carbide and tool steels that are tougher to sharpen than low alloy and "carbon" steels, silicon carbide and diamond stones / plates are your friends. They will be time saving and efficient versus natural (Arkansas, et al) or synthetic hones made from aluminum oxide and softer materials.

Hardness

Hardness is the ability to resist deforming when subject to stress and applied forces. Hardness in knife steels is directly correlated to strength and is generally measured using the Rockwell C scale (aka “HRC”).

Toughness

Toughness is the ability to resist damage like cracks or chips when subject to impact or “sudden loads”. Chipping is a knife’s worst enemy and never easy to fix. There are a number of different ways to measure toughness (i.e. Charpy, Izod) thus it’s less standardized than hardness when it comes to knives. In general, the harder the steel the less tough it’s likely to be.

Wear Resistance

Wear resistance is the steel’s ability to withstand damage from both abrasive and adhesive wear. Abrasive wear occurs when harder particles pass over a softer surface. Adhesive wear occurs when debris is dislodged from one surface and attaches to the other. Wear resistance generally correlates with the steel’s hardness but is also heavily influenced by the specific chemistry of the steel. In steels of equal hardness, the steel with larger carbides (think microscopic, hard, wear resistant particles) will typically resist wear better. However, carbides can become brittle and crack, thus decreasing toughness.

Corrosion Resistance

Corrosion resistance is the ability to resist corrosion such as rust caused by external elements like humidity, moisture and salt. Note that a high resistance to corrosion does involve a sacrifice in the overall edge performance.

Edge Retention

Edge Retention represents how long the blade will retain its sharpness when subject to periods of use. It’s what everyone talks about these days but unfortunately the measurement of edge retention lacks any defined set of standards and so much of the data is subjective. For me, edge retention is a combination of wear resistance and an edge that resists deformation.

 

[McFeeli]

Diamonds always help, but to answer your question. Some steels are literally harder. While 420 may have a hardness of 57-58HRC, something like S90V can be closer to 60-61HRC. ZDP is infamous for being a difficult steel to sharpen and I've seen it the whole way up to 67.

I'm no metallurgist so that's about the extent of my knowledge. Luckily there's a whole lot of great bladesmiths who know a lot more than me!

 

[Gvard]

Different steels have different alloying components, which form different carbides and those can be very resistant to abrasion. For example, steels with high vanadium content (like 10v) will form vanadium carbides which can't be abraded/sharpened by commonly used abrasives, like arkansas stones or aluminum oxide, since the carbides are harder than the abrasives. That's why it's always recommended to use diamond as an abrasive for such steels.Simple steels like 1095 can be sharpened on any abrasive, since it doesn't contain any of those high hardness carbides. If you use diamond, you can be sure that the steel is being sharpened, it isn't any more difficult, just may take a couple of swipes more than lower alloy steels.

 

[Obsessed with Edges]

• Thick grinds at/behind the edge. To me, this is the biggest PITA with virtually any blade, whether it's a wear-resistant steel or not. Blades needing a lot of thinning behind the edge will take a lot of work, regardless.
• Obtuse (very wide) edge angles. If trying to match factory angles that are too wide, it'll be a lot more challenging to get good cutting performance out of an edge, if it's too obtuse to cut well even on it's best day. Narrowing edge angles down to 30° inclusive or lower will make a big improvement, and will also make resharpening much, much easier.
• Using abrasives not well-suited to the steel type. With high-vanadium steels (greather than ~ 3% vanadium or so), diamond works best over the entire grit range. At coarser grinding of the same steels, SiC can work OK, but not as cleanly at the finishing end, as with diamond (or CBN). With other fairly wear-resistant steels with not so much vanadium, most any synthetic abrasives (aluminum oxide, silicon carbide, diamond, cbn) usually work well. But none of the moderately or highly wear-resistant steels like 440C, 154CM, D2 and beyond, will sharpen up very easily on natural abrasives (Arkansas stones). Natural stones work best with simple carbon and low-alloy stainless (1095, CV, 420HC, 440A, etc).
  
• Using hones too small for the task at hand. Heavy grinding jobs attempted with very small hones will take a LOT LONGER to accomplish. It's doable, but be prepared to spend up to 4X the time (maybe longer) to get the job done. Other problems come with spending that much time in grinding, like (1) fatigue, which makes for sloppy work, and (2) the stones get heavily loaded with swarf, necessitating frequent cleaning and interrupting the work. Small stones will also wear much faster (dishing, glazing, etc), if frequently used for heavy grinding tasks.

 

[Bo-dacious]

Okay these are making a lot of sense. So as a rule of thumb, any high end /high wear resistance/high carbide steel is best sharpened with diamond plates rather than regular stones? Im buying am edge pro apex so I'll have to buy the diamond plates too.

Thanks guys,

Bo

 

[Obsessed with Edges]

Okay these are making a lot of sense. So as a rule of thumb, any high end /high wear resistance/high carbide steel is best sharpened with diamond plates rather than regular stones? Im buying am edge pro apex so I'll have to buy the diamond plates too.

Thanks guys,

Bo

With diamond plates, you'll see the biggest benefit on steels with 3% or more vanadium, in particular. With a diamond hone, a steel like S30V (4% vanadium) or even S90V (9% vanadium) can be as simple to sharpen as a 420HC blade on an India stone (aluminum oxide), or a 1095 blade on an Arkansas stone, with all other variables being equal (grind thickness, edge angle, etc). Without the diamond, S30V takes on a whole different personality, and not in a good way.

Other steels that get most of their wear-resistance from something other than vanadium, like D2 or ZDP-189 (both with most of their wear resistance coming from chromium carbides), can still be sharpened up on most any man-made abrasive type like AlOx, SiC, diamond, etc. But with those, you may still notice better results with diamond, especially at the high-grit finishing end. I still prefer using diamond for finishing D2, for example. But with these steels, there's more leeway and flexibility as to which synthetic stone type you may want to use, for your own preferences.

 

[Bo-dacious]

The edge pro has course, medium, and fine diamond stones. (or medium, fine, extra fine, whatever.) on a high wear resistance knife, can I do the diamond stones, then move to a higher grit stone or polishing film? Like go from diamond to stone just to get that extra high grit?

Thanks,

Bo

 

[Bo-dacious]

Obsessed: thank you. So vanadium heavy steel is what you want to sharpen on diamonds and also other high wear resistance steels.

I appreciate it,

Bo

 

[Blues]

The Edge Pro 2300 and 4000 grit stones are bonded diamond hones.

You can also use the Fine / Super Fine diamond hones they have on the site. (I believe they were from Eze-Lap when I purchased mine years ago.)

Eventually they'll have the entire line of bonded diamond stones that diemaker is building for them which will provide further options.

 

[Obsessed with Edges]

The edge pro has course, medium, and fine diamond stones. (or medium, fine, extra fine, whatever.) on a high wear resistance knife, can I do the diamond stones, then move to a higher grit stone or polishing film? Like go from diamond to stone just to get that extra high grit?

Thanks,

Bo

On high-vanadium steels (3% or more), the high-grit finishing end is really where you'll always want the diamond, especially. Lesser abrasives at finer grit (< 10 micron or so) will have trouble cutting, shaping or polishing the vanadium carbides in the finishing stages.

At coarser grits used for setting bevels or reprofiling, simpler abrasives of aluminum oxide or SiC can still 'scoop' the whole carbides out of the softer matrix steel (think of a backhoe 'scooping' big rocks, in-whole, out of the soil). But they still won't do much to actually cut them specifically or reduce their size.

ALL of this isn't to say you can't get a certain level of acceptable sharpness using something other than diamond on some of these steels. But in doing so, you'll be giving up a bit in sharpness and polish (and likely edge durability), as compared to finishing with diamond.

 

[Bo-dacious]

Blues: okay so which is finer, the super fine diamond plate or the 2300 and 4000 grit bonded diamond stones?

Obsessed: okay, I have a bit better idea what to sharpen with now.

Thanks guys,

Bo

 

[Blues]

Blues: okay so which is finer, the super fine diamond plate or the 2300 and 4000 grit bonded diamond stones?

The 2300 and 4000 grit bonded hones will be much finer than the super fine diamond plate.
You can use that super fine diamond plate for removing metal fairly quickly, (use a light touch).

The other hones are finishing / polishing hones. You need to have already established your blade / bevel profile before moving on to those for removing any remaining remnants of a burr and polishing. If you're knife isn't already sharp before moving to the 2300 / 4000 hones, you're wasting your time...and your money. They are not designed to profile the blade.

If you read the couple of reviews on the Edge Pro site for the Super Fine and Fine diamond hones, the reviewers likened them to the standard Edge Pro 220 stone. Think of them as "coarse" stones.

 

[Bo-dacious]

Is there a link someone can send me that tells me the ingredient content of just the common steels? Or at least the vanadium content so I can tell if I should sharpen it on diamond stones? I found one but it had hundreds and hundreds of steels in it. It was hard to wave through.

Blues: yes, I only profile on low grit, I only hone on high grit.

Thanks man,

Bo

 

[Blues]

Bo, go back to the link that I sent you earlier...

http://knifeinformer.com/discovering-the-best-knife-steel/

Any of the steels listed in the Ultra Premium and Premium lists would benefit from the use of diamond hones.

The High End steels will also work well with diamond hones but can also be worked with Silicon Carbide and Aluminum Oxide (including ceramic). D2 can also benefit from diamonds because of its wear resistance.

As you go further down the list the need for diamond as opposed to more traditional hones becomes less and less.

You don't need an advanced degree in metallurgy. The main thing is to familiarize yourself with the steels in the top couple of categories that will benefit most from diamonds...and save you both time and effort.

 

[Obsessed with Edges]

Is there a link someone can send me that tells me the ingredient content of just the common steels? Or at least the vanadium content so I can tell if I should sharpen it on diamond stones? I found one but it had hundreds and hundreds of steels in it. It was hard to wave through.

Blues: yes, I only profile on low grit, I only hone on high grit.

Thanks man,

Bo

When I search for alloy content for various steels, using (on Google) a search string like '420HC steel composition' will produce lots of direct links to that specific info. Lately, I've even noticed that Google itself will put that info directly in a window at top-of-page, for at least some steels.

Barring that, I reference a site called 'zknives' a LOT, for such info. Their database is MASSIVE and their page will load very slowly if your query is too general in nature. But with the specific alloy name ('S30V', 'CPM-D2', 'AISI-1095') you can search with a string like 'zknives S30V', and you should see a linked search result to a composition chart on their site, for that steel. If you happen to know a steel's proprietary manufacturer, going directly to their site is often a good source of the most accurate info. I know Sandvik, in particular, has a lot of great reference material about their steels (12C27, etc).

 

[Bo-dacious]

Gvard: you're talking vanadium in carbides, not free vanadium I think it's called, right?

Blues: okay I will reread that post (3rd time now lol). Thank you, that's what I'm looking for. The steels all in one list!

Obsessed: great, thank you. I will try using zknives for my searches. It's nice to have a resource on which I can just look up the steel when I get a knife to sharpen.

Thanks guys,

Bo

 

[Wowbagger]

• Thick grinds at/behind the edge. To me, this is the biggest PITA with virtually any blade, whether it's a wear-resistant steel or not. Blades needing a lot of thinning behind the edge will take a lot of work, regardless.
• Obtuse (very wide) edge angles. If trying to match factory angles that are too wide, it'll be a lot more challenging to get good cutting performance out of an edge, if it's too obtuse to cut well even on it's best day. Narrowing edge angles down to 30° inclusive or lower will make a big improvement, and will also make resharpening much, much easier.
• Using abrasives not well-suited to the steel type. With high-vanadium steels (greather than ~ 3% vanadium or so), diamond works best over the entire grit range. At coarser grinding of the same steels, SiC can work OK, but not as cleanly at the finishing end, as with diamond (or CBN). With other fairly wear-resistant steels with not so much vanadium, most any synthetic abrasives (aluminum oxide, silicon carbide, diamond, cbn) usually work well. But none of the moderately or highly wear-resistant steels like 440C, 154CM, D2 and beyond, will sharpen up very easily on natural abrasives (Arkansas stones). Natural stones work best with simple carbon and low-alloy stainless (1095, CV, 420HC, 440A, etc).
  
• Using hones too small for the task at hand. Heavy grinding jobs attempted with very small hones will take a LOT LONGER to accomplish. It's doable, but be prepared to spend up to 4X the time (maybe longer) to get the job done. Other problems come with spending that much time in grinding, like (1) fatigue, which makes for sloppy work, and (2) the stones get heavily loaded with swarf, necessitating frequent cleaning and interrupting the work. Small stones will also wear much faster (dishing, glazing, etc), if frequently used for heavy grinding tasks.

David,
Very nicely done ! ! ! ^