Hardness vs Toughness and steel choices

B

Blowtorches and Tweezers

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I have read widely on the subject for six months and I am still unclear on a few things and looking for advice.

I am a hobbyist stone carver who modified many stock tools over the years. I am now making some of my own carving tools, similar to chisels but with double edged bevels that scrape, pry and torque. I tried using Magnacut steel at HRC 62 and was generally quite pleased. Most commercial tools of this type are hardened to the high HRC 50s and they don't really do what I want as I can't really get them thin enough without bending.

My only issue with Magnacut at HRC 62 is that i do get some tiny flea bite chips on the edges. Would I do better to try it HRC 60 or 64
Is absolute hardness more resistant to damage on the edge to a certain point or is it certain to be more brittle under any strain ? What I do not want is an edge that permanently bends exceeding the elastic modulus. An edge that bends and springs back would be fine.
Would the steels that harden to the high HRC 60s be worth trying? Would edges on carbon steels like 52100 or 8670 perform any differently than Magnacut ?

Thanks for any advice.
 
Higher hardness normally means higher yield strength so more effort it takes to deform. Once you have failure with higher hardness it usually means bigger chips.

An unpopular opinion, but, I like 62 Rc Magnacut better than when it is at higher hardness as I have less of the flea bite micro chips with my use.

If I was having recurring micro chipping I would look to a different steel. If you want to keep stainless AEB-L is tougher than Magnacut and has excellent edge stability.

If stainless is not a concern I would try 80CrV2 as I have found it to be a beast of a low alloy when it comes to abuse and it is easy to heat treat.
 
Seedy Lot said:
Higher hardness normally means higher yield strength so more effort it takes to deform. Once you have failure with higher hardness it usually means bigger chips.

An unpopular opinion, but, I like 62 Rc Magnacut better than when it is at higher hardness as I have less of the flea bite micro chips with my use.

If I was having recurring micro chipping I would look to a different steel. If you want to keep stainless AEB-L is tougher than Magnacut and has excellent edge stability.

If stainless is not a concern I would try 80CrV2 as I have found it to be a beast of a low alloy when it comes to abuse and it is easy to heat treat.
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This (yield strength) is what I was wondering so I am glad you chimed in. I bought some AEB-L a few months ago to try out over the winter. Stainless is not a big factor, just a convenience. Any thoughts on hardness ?
 
JoeBusic said:
How about a picture of your tools, to visualize "thin enough". I believe it's an impressive set.
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I am trying to be a bit discrete for now re pics in case it becomes something I cam make commercially, but my thin is not that thin compared to knife making. My edge would not cut your skin without a fair amount of pressure applied.
 
Blowtorches and Tweezers said:
This (yield strength) is what I was wondering so I am glad you chimed in. I bought some AEB-L a few months ago to try out over the winter. Stainless is not a big factor, just a convenience. Any thoughts on hardness ?
Click to expand...
Around 62 Rc is always a good hardness to try.

I have found at 60 Rc i will get a little edge roll with bone contact with sloppy big game butchering but some where around 61-62 Rc I don't experience the rolling issues any more.
 
How about getting some carbide tipped tools and modify the tip for your needs.
Steel choice, based on hardness and carbide amount, ApexUltra would fit nicely. It could be grain refined easily for added strength.
 
we can recommend steels until the cows come home. Geometry is king, try making your bevel just a few degrees more obtuse. I do agree that there might be a better steel for the application like 1V, CD1, and 3V could have a greater potential for durability in this application.
 
Thescrawnylumberjack said:
we can recommend steels until the cows come home. Geometry is king, try making your bevel just a few degrees more obtuse. I do agree that there might be a better steel for the application like 1V, CD1, and 3V could have a greater potential for durability in this application.
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Totally agree about geometry but i find it really interesting that no general consensus exists for which steels and which heat treat are best for edge stability. I have read all of Larrin Thomas's work but it still seems like it is an under tested aspect of blade design.

I am rather new to all of this but I do enjoy the research.
 
Blowtorches and Tweezers said:
Totally agree about geometry but i find it really interesting that no general consensus exists for which steels and which heat treat are best for edge stability. I have read all of Larrin Thomas's work but it still seems like it is an under tested aspect of blade design.

I am rather new to all of this but I do enjoy the research.
Click to expand...
It’s a very tedious process to create charpy and catra samples coupled with the fact there’s no standard test for edge stability. Every steel is different even the same steel varies from melt to melt. In most standard cutting applications I’ve always found the harder the better. Exceptions apply to large blades or higher impact forces. Typically for me 63-65 hrc on most steels. Sometimes more but very rarely under 63.
 
B Blowtorches and Tweezers you read this Larrin article?

knifesteelnerds.com

What is Edge Stability? - Knife Steel Nerds

Thanks to Keith Nix and Benaiah Brabant for becoming Knife Steel Nerds Patreon Supporters! The vote is still open on Patreon for what equipment will be purchased for future research. Edge Stability I got help directly from Roman Landes in writing this article (Thanks Roman!). The content below...
knifesteelnerds.com knifesteelnerds.com
 
Blowtorches and Tweezers said:
I have read widely on the subject for six months and I am still unclear on a few things and looking for advice.

I am a hobbyist stone carver who modified many stock tools over the years. I am now making some of my own carving tools, similar to chisels but with double edged bevels that scrape, pry and torque. I tried using Magnacut steel at HRC 62 and was generally quite pleased. Most commercial tools of this type are hardened to the high HRC 50s and they don't really do what I want as I can't really get them thin enough without bending.

My only issue with Magnacut at HRC 62 is that i do get some tiny flea bite chips on the edges. Would I do better to try it HRC 60 or 64
Is absolute hardness more resistant to damage on the edge to a certain point or is it certain to be more brittle under any strain ? What I do not want is an edge that permanently bends exceeding the elastic modulus. An edge that bends and springs back would be fine.
Would the steels that harden to the high HRC 60s be worth trying? Would edges on carbon steels like 52100 or 8670 perform any differently than Magnacut ?

Thanks for any advice.
Click to expand...
If the geometry is set and can’t be changed and at 62 HRC you are getting micro chipping then the logical conclusion is to try a tougher steel at that hardness. So you could try AEB-L or 52100 or 80crv2 or many others. Making MagnaCut harder doesn’t sound like a good idea on the surface, but stone cutting and scraping is very different I assume from how normal knives are used. You could try MagnaCut at lower hardness and see if it starts rolling at your geometry. I also don’t know how much wear resistance matters to you, with stone it seems like it would matter. I would probably try MagnaCut at lower hardness first and see if it works then try AEB-L at 63 or so and go from there. Edge stability is very highly correlated to hardness until you start chipping.
 
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