I Tested the Edge Retention of 48 Steels

Larrin - would you be willing to test something done with UFHT? I vaguely asked about this earlier, but had no idea there was any such official thing. I try to make all of my tools open atmosphere so that I don't have to send them out, and I've gotten lucky in some cases. XHP tolerates it and the result seems to be good (or good enough). There are obviously more plain steels that don't mind a really fast heat and quench (52100 seems to be OK with it for plane blades that are used in a favorable orientation to rolled stock).

Then, I saw an article the other day about UFHT, because my first effort with AEB-L this past week didn't bring high enough hardness (partially my fault) and the same ease in getting a decent plane iron didn't materialize. I'll try once more getting to higher heat before quench.

https://www.vibgyorpublishers.org/content/ijmmp/fulltext.php?aid=ijmmp-3-021

I don't know if testing the difference of some popular steels heated "ultra fast" vs. conventional would be worth covering on your site or testing, but it may be interesting for people with limited means (no controlled atmosphere, but the ability to heat and quench quickly at a high temp). I know from trial and error which steels tolerate this well in my shop, but suspect the failure with AEB-L vs. XHP may have to do with what the steel needs before it's quenched (time to dissolve carbides, that for some reason, XHP seems to be fine without).

I can talk at length about what I can see the difference from and what i can't, but that doesn't create any reliable data.
 
All of the high heating rate studies I am aware of are on hypoeutectoid steels (low to medium carbon) which are rather different because carbides are fully dissolved by the time the steel is austenitized. High carbon steels require higher temperature and/or longer soaking times to dissolve sufficient carbide.

Using a forge to heat steel is not an “ultra fast” method. Think more like induction heating. Salt pot furnaces would be a medium heating rate.
 
Larrin, if there was an edge-stability contest for blades, with the winning edge being able to sustain the least amount of edge damage (either from rolling/denting or chipping/cracking) by a calibrated, perpendicular blow from a bar of H8 steel -- something like chopping a hardened nail.

The entry requirements for the blade would be a V-edge geometry of 15 dps and an edge width of 0.015 inches. And the edge of that steel alloy had to have wear resistance in the S30V range at 60 Rc.

What steel alloy would you pick and how hard would you heat treat it for the best balance of strength and toughness?
 
Larrin, if there was an edge-stability contest for blades, with the winning edge being able to sustain the least amount of edge damage (either from rolling/denting or chipping/cracking) by a calibrated, perpendicular blow from a bar of H8 steel -- something like chopping a hardened nail.

The entry requirements for the blade would be a V-edge geometry of 15 dps and an edge width of 0.015 inches. And the edge of that steel alloy had to have wear resistance in the S30V range at 60 Rc.

What steel alloy would you pick and how hard would you heat treat it for the best balance of strength and toughness?
An edge stability test acts differently than an edge impact test. Edge stability tests are much more controlled by strength where edge impact is more pure toughness. A blow from a bar of steel is very hard on a knife, even with relatively low energy. You would be surprised how small the love taps are that will devastate a 15 dps edge even with tough steels. Assuming it is a true 15 dps edge and not the typical hand sharpened edges. You would be likely be exceeding the edge bevel height with your impact if it had any force to it.

Because it is a true toughness test the toughness matters the most and the hardness less so. So high toughness would be the main requirement. Your "wear resistance in the S30V range" then sets extra requirements. That depends on what counts as in the "range" of S30V, like for example CPM-4V and CPM-CruWear would be a bit less than S30V, if those aren't close enough you'd have to go up to CPM-M4 probably. Despite toughness being the most important I think higher hardness with those lower carbide steels would offer better toughness than something like CPM-9V at low hardness where the wear resistance would be similar to S30V. There could be an interesting crossover there but it would become somewhat unrealistic. As can anything if we are focusing on only one test. Like if we were maximizing CATRA we would end up with a diamond blade. Or sticking with steel would be 72 Rc Rex 121 at 6 dps or some crazy edge angle. CPM-4V and CPM-CruWear are good choices for the edge impact test because of the relatively low carbide volume (<10%) and small carbides, but relatively high wear resistance at that carbide content because of the harder vanadium carbides. Maximizing toughness for a given level of wear resistance is usually done by having all vanadium carbide. You set the level of toughness-edge retention by how much vanadium carbide there is after heat treating. In terms of maximizing toughness with heat treating there are a few things we can do. We of course aren't going to shoot for 64 Rc. Somewhere in the range of 58-62 Rc would be best, has to be high enough to meet your criteria of matching S30V for wear resistance. In toughness testing of CPM-CruWear and 4V better toughness was achieved by using a low temper (400F) rather than a high temper (1000F). Then you have to avoid the many pitfalls of heat treating, ie don't austenitize too high, avoid decarburization, etc.
 
I tried AEB-L courtesy of these tests and your page on it - I mentioned failure with AEB-L, but I think I was wrong. I heated the iron in open atmosphere and left it at high heat for a couple of minutes (not 10, but just shooting for getting some of the carbides dissolved and not ruining the steel going overboard). Fairly sure the initial softness (same thing this time) is just a decarb layer as after honing a few times, the iron is hard and has great wear resistance. I never would've thought to try it. The array that I tested including feet planed (which is sort of a cross to a push cut as you mentioned, but with some side forces at the same time would be like a 45 degree push cut instead of straight in)..

1084 steel - 997 feet
1095 steel - 836 feet (toughness problems with the initial edge that eventually wore off, but small failures in the initial edge in my experience with wood greatly reduces feet planed)
O1 - 1231 feet
52100 - 1235 feet
AEB-L - 2000 feet on average in two tests (a huge surprise!)

The hardness for all is similar (no way to test other than gauge how easily each sharpens on , though I don't know for sure with AEB-L - high heat, oil quench and then temper at 300F - it feels like 60 to low 60s

the AEB-L number seemed outlandish on the first test, so I did a second. Wonderful uniform wear - and maybe the material being wood leads to a different result than a silica impregnated card (I'm beginning to think that chromium carbides are the woodworker's friend -the AEB-L result is about even with 3V in a prior test vs. the O1 iron in this group, but it works on a wider variety of normal sharpening stones that woodworkers use.

I really ran this test to see if a higher hardness 52100 iron would beat my "regular", the O1 steel iron at a higher hardness, and threw in the AEB-L expecting not to see much from it as I don't know what I'm doing with it yet with my atmospheric HT limitations. You mentioned above in your write up that you expected something different for O1 (I don't remember what it was, but if you said similarities to 52100, I found that).
 
oops...test how easily they sharpen on a washita, which has particles around 62 hardness...that's my testing bed (for feel) along with a settled in india stone for hardness, but it's thrown off by chromium and other carbides, especially if they're big.

There are a lot of people who probably won't believe you can actually gauge anything like this, but you can if the steels are in a fairly narrow range (of alloys and hardness) close to the particle hardness in the stone, and you only sharpen like items (I can't judge knife edges well because their contact with the stone is different, usually smaller)
 
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Maxamet
CPM T15
Rex 76
Rex 45
Spy27
XHP
420
 
In a big study comparing 154CM and CPM-154 there was no difference so D2 Vs CPM-D2 is likely to be the same. https://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/
Very interesting. I did some searches a while back with 154cm vs 154cpm and it was claimed that cpm154 was a lot tougher and better edge holding than standard 154cm.
I am very glad to hear you refute this claim and I am very tempted to purchase your book I seen on Amazon come next payday.
I find it refreshing to hear some truth on various steels as opposed to marketing hype.
Thanks for your contributions to the steel and knife industry sir. And for teaching us that are less informed about metallurgy and knives in general.
 
...I am very tempted to purchase your book I seen on Amazon come next payday.

Do it! Probably the best purchase you can make if you’re wanting to learn more about steel for knives. I’d snag it from CollectorKnives instead though. Mike has it for the same price there.

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Very interesting. I did some searches a while back with 154cm vs 154cpm and it was claimed that cpm154 was a lot tougher and better edge holding than standard 154cm.
I am very glad to hear you refute this claim and I am very tempted to purchase your book I seen on Amazon come next payday.
I find it refreshing to hear some truth on various steels as opposed to marketing hype.
Thanks for your contributions to the steel and knife industry sir. And for teaching us that are less informed about metallurgy and knives in general.
The toughness of CPM-154 is better, the edge retention isn’t.
 
The toughness of CPM-154 is better, the edge retention isn’t.
I feel that some context is important here. There is no improvement to edge retention shown in CATRA testings, but in something like rope cutting tests PM steels do tend to perform much better than their non-PM counterparts.
 
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