I would really like to see an edge retention test with the various steels normalized for toughness.

Fixall

Fixall

Brian
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Knifemaker / Craftsman / Service Provider
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That title probably doesn't make sense. I'll try to explain what I mean.

Typically when we see an edge retention test, we see one of two things. Either the blades normalized for hardness, with all the blades around the same hardness (say 61rc), which isn't really fair considering some steels can achieve much higher hardness compared to others. Or we see edge retention tests with various blade steels heat treated within a couple points of their max hardness, which also isn't really fair when some of those steels become too brittle for an edc knife for most people.

S35VN at 61rc is considered tough enough that manufacturers have no issue using it in knives and offer full warranty support with regular usage. Let's try using that as a baseline. At 61rc, S35VN measures 10ft-lbs on the Charpy Impact Test. Heat treat a bunch of blades with exactly the same edge geometry to the highest hardness possible, while still being able to absorb 10ft-lbs on the Charpy Impact Test. Test for edge retention. The winner is the "best" steel for an edc knife.

Or if S35VN at 61rc isn't tough enough... How about M4. I can't imagine many would say M4 isn't tough enough for an edc blade. At 61rc, M4 measured ~15ft-lbs on the Charpy Impact Test. Heat treat a bunch of blades with the same edge geometry to the highest possible hardness, while still being able to absorb 15ft-lbs on the Charpy impact test. Test for edge retention.

Am I missing something? Other than the difficulty of fine tuning the heat treatments to a particular level of toughness, is there a flaw in the testing that I'm not seeing? It's late, there's probably something basic I'm overlooking.
 
The expense.
Achieving a set toughness would require many attempts in order to dial it in.
And there is a lot more scatter in charpy data than there is in Rockwell hardness.

I also kind of don't see the point.
 
Fixall said:
That title probably doesn't make sense. I'll try to explain what I mean.

Typically when we see an edge retention test, we see one of two things. Either the blades normalized for hardness, with all the blades around the same hardness (say 61rc), which isn't really fair considering some steels can achieve much higher hardness compared to others. Or we see edge retention tests with various blade steels heat treated within a couple points of their max hardness, which also isn't really fair when some of those steels become too brittle for an edc knife for most people.

S35VN at 61rc is considered tough enough that manufacturers have no issue using it in knives and offer full warranty support with regular usage. Let's try using that as a baseline. At 61rc, S35VN measures 10ft-lbs on the Charpy Impact Test. Heat treat a bunch of blades with exactly the same edge geometry to the highest hardness possible, while still being able to absorb 10ft-lbs on the Charpy Impact Test. Test for edge retention. The winner is the "best" steel for an edc knife.

Or if S35VN at 61rc isn't tough enough... How about M4. I can't imagine many would say M4 isn't tough enough for an edc blade. At 61rc, M4 measured ~15ft-lbs on the Charpy Impact Test. Heat treat a bunch of blades with the same edge geometry to the highest possible hardness, while still being able to absorb 15ft-lbs on the Charpy impact test. Test for edge retention.

Am I missing something? Other than the difficulty of fine tuning the heat treatments to a particular level of toughness, is there a flaw in the testing that I'm not seeing? It's late, there's probably something basic I'm overlooking.
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I agree that comparisons with all steels at say 61 HRC don't represent how you might choose to actually use each steel.
Larrin's charts give enough info to at least estimate what you are after. He has given formulas for how properties vary with hardness etc. It would be a little tedious, but you could construct the data for at least a few types of steel of interest. I'd be interested to see the comparisons between say 3V at 61, m4 at 63-64, and so on, using realistic hardness choices for each.
 
You're basically asking for the pareto frontier of a wear resistance vs toughness dataset.

I think Larrin Larrin usually publishes wear resistance vs hardness or toughness vs hardness but it seems like a wear resistance vs toughness plot should be possible. Just keep in mind that I think for some steels you can get to the same toughness at different wear resistances based on HT protocol.
 
In some ways it would probably be boring to some, Brian: For example, 3V won't go much higher than 61, and then again, not many care about Maxamet below, say, 65.

Larrin tries to plot toughness for several HRC, if available. It would of course be great to have such line plots for all interesting steels. I'm guessing it's a matter of time to complete the data ....

Roland.
 
Obviously doing tests where things are “dialed in” to some target are much more difficult and time consuming to perform, and requires many more samples and dedicated time. Even in scientific journals such tests are rare.

Doing a range of toughness tests at different hardness levels and heat treatment parameters has been done for several steels of course. Those are quite large studies though the information is only really relevant to knifemakers as the data is very specific.

For edge retention results they are generally simpler than for toughness. It’s just carbides and hardness essentially. If the edge geometry is identical, that is. I do some normalizing of data for my wear resistance-toughness charts in certain articles like MagnaCut where I showed where it fits in terms of wear resistance-toughness balance. Also everything had to be normalized for my steel ratings found in my book and the Patreon. That uses simple equations and educated guesses where necessary to compare steels directly.

Another issue with specific comparisons is that no one can agree with what that should be. What test is best for testing edge strength? edge toughness? Edge retention? Tip strength? Is 15 dps the baseline? 20 dps? Sharpened to high polish? Coarse edge? High hardness? Medium hardness? Heat treatments designed to match manufacturers or custom makers? If there’s one thing I’ve learned it’s that no matter what parameters I use there is someone who will say that it has no relevance to what they wanted to know. (Spyderco heat treats it to 62 not 60! No one sharpens like that! Your custom heat treatment doesn’t reflect the manufacturer knives! Your heat treatment was poorly done, if you had done it this other way it would have shown better properties! Your tests end at this level of sharpness but I only care up until this other level of sharpness and the results would be different in that scenario!) Going more specific doesn’t please anyone.
 
Send them to me. I live near a landfill and can easily dispose of them for you.
(I need to send you a couple of bucks for that post. A good setup for a punchline is worth money.)
 
knarfeng said:
Send them to me. I live near a landfill and can easily dispose of them for you.
(I need to send you a couple of bucks for that post. A good setup for a punchline is worth money.)
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I was expecting a wiseass reply from Shawn, but you, Frank, I'm simply taken aback and overcome.

I'll send you my bill. Couple bucks ain't gonna cover it. 😂
 
Yea…. Keep me up past my bedtime and get a few drinks in me and I start thinking i’m a bit more clever than I really am.

Happy Independence Day everyone!
 
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Fixall said:
Yea…. Keep me up past my bedtime and get a few drinks in me and I start thinking in a bit more clever than I really am.

Happy Independence Day everyone!
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I don’t think anyone is trying to criticize your idea just giving some reasons why it isn’t quite as simple as it might sound on the surface.
 
Larrin said:
I don’t think anyone is trying to criticize your idea just giving some reasons why it isn’t quite as simple as it might sound on the surface.
Click to expand...

I didn't take any of the posts that way. :)

I just woke up today and was thinking of all the various difficulties the idea would pose and was dreading coming back to the thread a little bit, lol! You and others basically brought up all the of the problems I thought of, plus several more. :P

Another problem I was thinking about is that the heat treat would still have to be dialed in for each individual knife because of the differing geometry. ZDP-189 at 65rc could be sufficiently tough to use on a knife with a certain geometry, and then be to fragile to use on a knife with a different geometry.

Meh. I should have thought the idea through a bit more. 🤷‍♂️
 
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