Blade Hardness

It depends very heavily on the steel used and the edge geometry, but I normally shoot for 61 to 62 HRC in hunters. Depending on the steel, if I go higher, I find that I will develop a more polished edge that does not "feel" as sharp, even though it is, due to the less toothy aggressiveness in the draw. Knives that will do more push cuts with and ultra-fine edge, like many kitchen knives, I will push beyond 62, and the only ones that I ever go below 60 with is specialized choppers. Going below 60HRC is invariably a waste of potential for the steels I use for hunters.

Ease of sharpening often comes up with this topic, but in almost every case ease for sharpening is more a issue of geometry. I have been able to push my steels to the theoretical limits of hardness and they were still far short of the softest sharpening stone, and we have diamond hones... I don't think anybody is that good of a heat treater! A very fine edged kitchen knife, even at 64HRC can be brought back in a couple passes on the stone, but with a much bulkier geometry even a 58HRC blade is going to take a lot of passes to remove the material to reengage the very edge again, unless you lift the angle higher and higher, until you have to regrind the blade to bring it back. There are certain factory made knives that are often brought to me because the user cannot get them sharp, I always ask if they want me to sharpen them so that they need to bring it back to me, or if they want me to sharpen them so they can do it the next time. If they want the latter, I simply regrind the blade and never need to see it again.
 
Kevin R. Cashen said:
Ease of sharpening often comes up with this topic, but in almost every case ease for sharpening is more a issue of geometry. I have been able to push my steels to the theoretical limits of hardness and they were still far short of the softest sharpening stone, and we have diamond hones... I don't think anybody is that good of a heat treater! A very fine edged kitchen knife, even at 64HRC can be brought back in a couple passes on the stone, but with a much bulkier geometry even a 58HRC blade is going to take a lot of passes to remove the material to reengage the very edge again, unless you lift the angle higher and higher, until you have to regrind the blade to bring it back. There are certain factory made knives that are often brought to me because the user cannot get them sharp, I always ask if they want me to sharpen them so that they need to bring it back to me, or if they want me to sharpen them so they can do it the next time. If they want the latter, I simply regrind the blade and never need to see it again.
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This is the best stuff I have ever heard. I knew this but I always heard people that been doing this way longer then me always talk about "I keep the hardness down so my customers can sharpen them easily" I always thinking the only knife that ever gave me problems was if it was to thick at the edge. And I suck at sharpening knives lol.
 
I see some of the older folks using files in the field to sharpen their knives even though they own stones at home. I think their just dressing up an edge temporarily with the file when they do that - I hadn't thought to ask until now. But I have noticed you need to know how to get rid of a burr if you do it that way. On the hunting knives I make I'm going to see how they respond to a file - if that was all a person had available and because that is what some people who I know do.

Thanks for the original post and thanks Kevin. This kind of answers 2 questions for me. On transitioning grinds and the hardness I was going to try for with my 1075. The thick tips won't sharpen as well as the rest of the edge and I'll need to work on getting my 1075 knives thin in order to be user friendly not just a certain hardness.
 
Volkert Forge said:
This is the best stuff I have ever heard. I knew this but I always heard people that been doing this way longer then me always talk about "I keep the hardness down so my customers can sharpen them easily" I always thinking the only knife that ever gave me problems was if it was to thick at the edge. And I suck at sharpening knives lol.
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The concerning thing for me is the idea that one should lower the blade hardness to accommodate easier sharpening, if that is the case, we can all go with that $5 Pakistan stainless special at Walmart. Strength and abrasion resistance are the properties that are needed for a long lasting and stable edge, the steel doesn’t know what object is wearing its edge way, be it grit or hair on game or the surface of an Arkansas stone, both are abrasion and/or deformation, just the stone is much more predictable on the deformation part. Logic dictates that lowering the hardness of a blade to allow the stone to easily abrade the edge, will also allow anything else that the edge encounters to do the same so, softening a blade for easy of sharpening is self-defeating. What has allowed this erroneous concept to survive is the real culprit, an overly bulky geometry, which will compensate for deformation, but is what made the blade harder to sharpen to begin with.

Now there is a point where hardness has gone too far, and that is when you get dulling due to micro-chipping. This is the ductile to brittle transition and I aim to have all of my blades very close to this tipping point for their given edge geometry, and that last part are the most important words in that sentence- for the given geometry. Geometry is based on application and using a sashimi knife to whack or chop anything would be disastrous, otherwise it wouldn’t be a good sashimi knife. I must also add that anytime I have seen micro-chipping in a blade with good geometry, further examination showed some undesirable condition inside the steel; a common one would be something like carbide networks in 1095 or W2 that was slow cooled in a forge or vermiculite for annealing, or enlarged grain size.

I was doing some knife edge testing a couple of years ago and I had my high temp salts go out of neutrality without knowing it. I discovered the problem during sharpening when I felt a heavier burr than I would ever get normally. The steel edge was deforming from the pressure on the stone much more than it should, despite a good Rockwell reading on the ricasso. Examining a cross section of the blade under the microscope revealed a V- shaped decarburized skin at the edge where the effects could penetrate more due to thickness. I rectified my salts immediately, but the point of the story is that it was the ductile nature of the edge giving me a large burr on the stone that told me, immediately, something was off in my standard process.
 
Kevin R. Cashen said:
Now there is a point where hardness has gone too far, and that is when you get dulling due to micro-chipping. This is the ductile to brittle transition and I aim to have all of my blades very close to this tipping point for their given edge geometry, and that last part are the most important words in that sentence- for the given geometry.
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And this is where I like to be. An edge that is a hair too thin and approaching chippy is very easily rectified by subsequent sharpening. The blade being a wedge means that the edge only gets thicker with each sharpening, making the edge more stable, but a thin blade still has plenty of room for many sharpenings before the edge is too thick to be a good slicer. Conversely, a thick geometry has already hit the wall on day one and is not only difficult to sharpen but will never be a good slicer to begin with. An axe with a great edge will cut hair but it won’t slice cucumbers.
 
I shoot for 61-62 on stainless like m390 or Elmax or 20cv . I grind the edge thin also because I know these steels can take it. I have tried to hand sharpen these with stones and quickly get frustrated and go to the grinder.
 
A2 blades 60-62 target...use a hardness tester. most times coming in at 61. I also do a liquid nitrogen soak before I double temper. I'm happy with the results.
 
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