Edge retention of hardened H1?

M

Mephtyrm

Joined
Jan 23, 2011
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I hear a lot that H1 is work hardened when it heats up like cutting a lot of cardboard(Which I cut a lot).
However, I've never seen anyone have a "Hardened" H1 blade do an edge retention test.
How does the edge retention compare to common steels when it is at the 60's of RC?
 
Serrated H1 has a lot of edge retention, but the plain edge has edge holding roughly on the same level as 12C27 in a Mora, which makes sense given the very low alloy content which means it has little to no carbides for wear resistance. I doubt the edge would heat up from cutting cardboard unless you've got entire sheets of it just being rolled by like newspaper being printed out and you're just sticking the knife in it to have several yards of cardboard get cut per second. I also doubt non-powered sharpening would do anything to heat it up either.

You may be able to artificially harden the blade by putting a full flat grind on it with a belt sander, which I believe would push the Rc past 62. Edge retention would probably be the same as any low alloy steel at that hardness range, which is hard to say, but perhaps like any old carbon steel blade like 1095 at high hardness. It still wouldn't have much wear resistance, but I guess if it's driven up to Rc 64+ it would be hard to differentiate from ZDP-189 or even D2 aside from not being as toothy. I think Sal mentioned the SE is Rc 68 at the very edge, making it harder than ZDP-189 and roughly the same hardness as pure chromium carbide.

It's interesting to say the least, and I think I might try it out on a Pacific Salt just to see how it works out.
 
I plan on having a Salt 1 reground by Tom Krein some time in the near future. I'd also like to see how the further work hardened H1 performs.
 
brets-ftw said:
please do, I think there was a for sales thread that had two reprofiled H1 knives, and was curious about the edge retention with new geometry. Ill see If i can find it

Edit: here is the thread,Ill contact the OP to see if he has any input to add

http://www.bladeforums.com/forums/s...nd-Salt-I-Custom-Regrinds!?highlight=regrinds
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If you could get his feedback that would be great. I've ordered a new Pacific Salt in plain edge to regrind. I think I might go with something like a zero edge FFG with a microbevel to really thin it out. I'm hoping the hollow ground blade won't complicate matters too much as I wouldn't be able to thin it out much without grinding the spine down as well.

What I'm really curious about is how thorough that work hardening process really is. It was mentioned that when one side would be flat ground, the other side would already be hard, which doesn't make too much sense to me since I figured work hardening was like taking a steel rod and repeatedly bending it back and forth until it snaps, and it would usually reveal that only the spot where it was deformed would be hardened and not the two ends furthest away from the deformation. I also don't feel that heat itself causes hardening, otherwise artificial hardening would be as easy as taking the thing to a blowtorch.

Knowing how deep into the steel the hardening goes also explains a few properties of the altered steel. Will the "hardened" section eventually be ground away from repeated sharpening sessions? Will the blade be as brittle as ZDP-189 at Rc 67+? Or will it have differential hardness and be tougher for it like the Diamond Blade Friction Forged D2?

It would be interesting if edge retention gets up there with ZDP-189. If the hardness rivals ZDP-189, I feel that alone would be worth it. Without having to bother with carbides, it should be able to take and hold a razor edge much easier, and perhaps be tougher as well. H1 in its standard form is described to take a razor edge like carbon steel and is tough enough to be bent at a 90 degree angle without breaking.
 
I PM'ed the OP of that post and he hasnt responded, I also added this thread URL so that he can post if he sees fit, Might try again.

and those are some interesting thoughts, Metalurgy is hard enough as it is with "standard" steels, these work hardening ones is a completely different animal I find
 
Mephtyrm said:
I hear a lot that H1 is work hardened when it heats up like cutting a lot of cardboard(Which I cut a lot).
However, I've never seen anyone have a "Hardened" H1 blade do an edge retention test.
How does the edge retention compare to common steels when it is at the 60's of RC?
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I'll jump in before Mete gets here. I can hear his teeth grinding already. Heating the blade has nothing to do with work hardening. Work hardening and cold working mean the same thing and can be accomplished with no addition of heat. Cold forging is one way to work harden metal, as is cold rolling. Copper, brass, and bronze tools/blades were work hardened by cold forging before steel was used. Heating above a certain point (the recrystallization temperature) will undo the effects of cold working, though this gets really complicated as the recyrstallization temperature is affected by the amount of cold working, and naturally enough is also alloy specific. Grinding and machining can work harden metal, but only in the thin layer that is affected just below the cut/grind, which might only be microns thick. Cold working/work hardening requires the plastic deformation of the metal, ie stressing it above it's yield strength. The exact processing of H1 is not widely known, but IIRC, involves work hardening and precipitation hardening, which is a heat treatment procedure. The exact temperature I have not seen for H1.
 
Yes, I would have assumed the work hardened portion is only microns thick as well, but if Sal mentions that the reason they don't flat grind it is because the other side becomes too hard to effectively grind by the time one side is done, then that obviously isn't the case. Though without a Rockwell hardness test of each section of the blade as it is ground, it would be hard to say. I suppose I'll have to see if one side is really harder to grind than the other as more metal is removed. Kind of wondering if Tom Krein knows this one.
 
So how would the back side cold work/plastically deform from grinding the other side of a 1/8" thick piece? I think the statement from Sal has been misquoted. I heard that it was done with hollow grinds because they are done on both sides at the same time, and high speed flat grinding one side at a time caused the blades to warp. However, this is a second hand quote, so Sal may not have said that either. The only way to know is to have him post as see what he says.
 
I had a long talk with someone that explained it something like this..... "You don't get much work hardening from sharpening and use, that all happens when the steel is compressed. When rolled is when H1 becomes hard from work hardening, it takes tons of force to compress the metal and cause the hardening." Then why such the difference in edge retention between plain edge and serrated edge? "Because a work hardened metal is only hard at the surface while the inner metal is softer. When ground for a plain edge the apex of the cutting edge ends up in the softer area of the metal while a off-set asymmetric serrated edge puts the apex of the cutting edge further into the "hardened metal" increasing the performance of the alloy."

So given that info I personally would only pick the serrated edge H1 or if it was a option a true chisel grind.
 
knifenut1013 said:
I had a long talk with someone that explained it something like this..... "You don't get much work hardening from sharpening and use, that all happens when the steel is compressed. When rolled is when H1 becomes hard from work hardening, it takes tons of force to compress the metal and cause the hardening." Then why such the difference in edge retention between plain edge and serrated edge? "Because a work hardened metal is only hard at the surface while the inner metal is softer. When ground for a plain edge the apex of the cutting edge ends up in the softer area of the metal while a off-set asymmetric serrated edge puts the apex of the cutting edge further into the "hardened metal" increasing the performance of the alloy."

So given that info I personally would only pick the serrated edge H1 or if it was a option a true chisel grind.
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Hmm, does that mean that a fully serrated blade is "wider" than a plain edge? Also, I kind of got two different definitions on work hardening and precipitation hardening. Work hardening which hardens the material through deformation, and precipitation or "age" hardening was described as heating the steel to about 400-700 deg C and holding it there for several hours, which basically sounds like the reverse effect of tempering to me, and seems similar to case hardening. The case of the latter would explain why the spine and edge seem to read at the same hardness(Rc 58), while the side of the blade seems to scratch easier than any other steel I've ever used.

Still, official word seems confusing:
TazKristi said:
H1 is a precipitation-hardened alloy. And yes, it is also work-hardened. Meaning that anything that you do that causes heat through friction will harden the steel further; it’s also important to note that tests have shown that it does not become brittle. The work-hardened properties of H1 have been proven by analysis independently performed by Crucible Specialty Metals. It is this that explains why an H1 blade with a SpyderEdge has better edge retention than it's PlainEdge counterpart. In the end, the analysis from Crucible found the Rc at the spine was 58, however at the edge it had increased in both the PlainEdge (to 65 Rc) and the SpyderEdge (to 68 Rc).

The Salt Series knives are being made and promoted to a market where corrosion resistance is important.

So, is H1 possibly just another flavor-of-the-month? Possibly, but hype can only go so far.

Kristi
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Tom Krein said he didn't know anything regarding the work hardening properties, though he did confirm that the reason why the blades are hollow ground is because of warping issues. Some have mentioned that warpage might contribute to the work hardening, though it's hard to say for sure.

Another theory is that there IS some minor work hardening going on during sharpening. Now typical sharpening shouldn't have any major contributions, but when you consider what actually happens when you raise a burr on one side and then move it to the other, that weakened piece of metal is constantly being deformed as you move the burr from side to side. Can't say for sure what significant effect it would ultimately have, though I feel sure that this phenomena isn't solely restricted to H1 steel, and that all blade steels will be work hardened to some minor degree.

In any case, I don't think anything definitive can be said without a series of Rockwell hardness tests. Though I feel this information would be worth finding out, mostly because if the precipitation hardening process is mostly why the SE version is that much harder, it would imply that the plain edged H1 knives would actually get softer with repeated sharpening.
 
I don't know anything about H1, but it sounds like it would benefit from steeling , more then other blades
 
Hawkings said:
I don't know anything about H1, but it sounds like it would benefit from steeling , more then other blades
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That would depend on whether it work hardens to a more significant degree than other steels. Again, until extensive testing is done, specifically Rockwell hardness tests, this is all just unconfirmed well-wishing. Though I suppose going through several cardboard boxes would make it immediately apparent whether edge retention is better than 12C27.
 
On the surface, quenching and tempering look almost exactly like precipitation hardening. However, the mechanisms and strength changes are different. It's also worth noting that both work hardening and precipitation hardening have peak percentage and temperatures respectively. Work hardening past a certain point won't produce a higher strength directly, and over heating a precipitation hardened alloy will soften it. The peak for work hardening is different for different alloys, and I need to double check my information before getting any more detailed.

Precipitation hardening alloys are solution treated by heating to a high temperature then quenching, often in water. They are then reheated to a lower temperature and held for various times, though the times tend to be much longer than the tempering times for steels, many hours or even days. Metals like H1 are work hardened, often by cold rolling, between these two heating cycles. This step increases the effectiveness of the precipitation hardening step and gives higher strength. The differences can be drastic. Dig around with the search function and find user Hammerfall's early posts on his submarine bearing material he uses for some knives.
 
knifenut1013 said:
"Because a work hardened metal is only hard at the surface while the inner metal is softer. When ground for a plain edge the apex of the cutting edge ends up in the softer area of the metal while a off-set asymmetric serrated edge puts the apex of the cutting edge further into the "hardened metal" increasing the performance of the alloy.
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Especially when talking about cold working by cold rolling blade stock, it is not something that happens just at the surface.

Also keep in mind that cold work generally doesnt increase tensile strength, just yield strength. It also decreases ductility. Thats a general statement, and exeptions certainly exist.
 
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