Another Convert for High Hardness (>63 HRc)

M

me2

Joined
Oct 11, 2003
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Looks like one fella at work changed his mind on high hardness blades. I bought some 1095 a while back and gave him a piece of it. We profiled the knives and he finished his and hardened it according to some tests we did on pieces of the 1095. The end hardness was 66.2 HRc. He hardened and finished it early last week and called to say he was very impressed with the edge holding. He used it to cut through some plywood and other scraps, make dinner and some other odd jobs and said he never thought it would hold up as well as it did. I have to get busy and finish mine and see how it works. I've got 2 others I'm working on made from unaltered files, other than grinding, so I'm anxious to see how they do as well. One file is of unknown origin, but tested ~64 HRc. The other is a Nicholson Black Diamond, with a good reputation and made just up the road in Apex, NC.
 
Yeah, the obsession with obtuse edges and supersoft stainless blades will hopefully pass. Then again the American people aren't getting smarter by the minute either.

They probably started making heavy user knives in stainless, those blades started cracking, so they made them supersoft, but with the edge supersoft it readily indented, so they made the edge obtuse...
 
Few stainless blades can actually get very hard, cutlery started with the 440A series which get to 60 HRC with a very high austenizing temperature, cold treatment and very low temper, they are usually ran much softer.

Use of such steels for really unsuitable knives like tacticals is probably what lead to the myth of hardness being opposed to sharpening, when in reality the opposite is true.

Me2, now you need to try some HSS, it has all the good points of hard carbon steel with more corrosion resistance, finer grain, and much better wear resistance.

-Cliff
 
I meant to ask how the Pinoy M2 knife review was going. I thought of ordering some 1/8" or 1/16" stock of M2 and grinding it to shape. I just havent thought of a way to get holes in it yet. I'd really like a balisong/utility w/ an M2 blade, but again, how do you drill what drill bits are made of (or close to it anyway)?
 
I have several M2 blades I need to both do some more work with and put up the information I have. You can buy M2 power hacksaw blades on rec.knives in various thickness. Chas posted information awhile ago on what drill bits he uses.

-Cliff
 
Cliff you mentioned F2 steel in an earlier post, I've been looking all over for it but can't find it? Could you help me out?
 
Several makers have mentioned F2. Its gonna be hard to come by, because I think its the only steel in the F series still being produced, and in very limited quantities. It may be completely out of production by now, but with some rather large stockpiles somewhere.
 
As a user, edge retention isn't a huge issue with me. If I were a manufacturer and put out high quality hard blades, I'd probably expect to get quite a few of them back with cracks, chips, etc. Retail makes $$$ with as few returns as possible and most people don't use their knives so much that hardness is an issue. (We're more likely to drop our knives than to use them heavily.)

Still, I would like to use a superhard knife for a few months just to see how I liked it. But money is an issue.

--Confed
 
I wasnt a believer until I saw some of the data on the high hardnesses. These hardnesses at 63.5 and 65 or 66 can actually correspond to peaks in toughness and ductility, then as the hardness goes down, the toughness and ductility have a trough, then rebound with even more softening to back up to surpass the previous peak, but usually at hardnesses of around 50-53 or even lower. The troughs seem to occur at temperatures associated w/ some sort of temper embrittlement (there are a couple of different kinds). For experimental grade steels, these troughs may not happen, but for commercial grades with less tightly controlled impurity levels, they are there. This is one reason some people prefer tool steels, since they are held to lower impurity levels and may not have as pronounced a trough as equivalent low alloy steels. The knives I've seen made with the high hardnesses are typically quite thin, with ~4" blades. They might break if dropped, but they are small and thin and therefore quite light and I doubt they'd break unless thrown into a hard floor. You could loose a tip if dropping on a ceramic floor, but that happened to one of my knives at 58 HRc when it fell out of my pocket, opened on hitting the floor (speed safe from Kershaw) and bounced and hit with the tip on the bounce. Like Confederate, I'd like to try one just to see what would happen. No production knives I know of other than spyderco, and not many makers will make blades like this, so expense may not be an issue. You have to do it yourself, and the most expensive part is figuring out how to shape the **** stuff if its already hardened.
 
I don't know if anyone's ever bothered testing regular production knives (like Cold Steel) to see how their advertised hardness corresponds to actual hardness. AUS 8A generally is advertised around 58 HRC, but can actually be 1 or 2 below that.

--Confed
 
There have been several checks on production hardness levels, many times they are much softer than reported. What is reported is in general the ideal hardness if everything goes right.

The high hardness steels are not as brittle as often implied, depending on the steel, as me2 noted making the steels softer can make them more brittle and weaker, hard=brittle is not a uniform rule.

In general rather than drawing hardness to get the necessary toughness, it is *much* better to switch steels and get one that is inherently tougher, this usually gives a much better combination of properties.

In general for me it isn't about edge retention as much as cutting ability, what you can cut, and ease of sharpening. You can take 1095 at 66 HRC and run it much thinner and do a lot more work with it than 1095 at 55 HRC.

-Cliff
 
TOPs runs their 1095 knives at 58 RC to get better ductility out of them (I assume?), I wonder if they know this hardness is practically the weakest 1095 can possibly get regarding torsional strength. I looked at the charts for 1095 you have in you steel guide Cliff, and this alarmed me.

Basically your saying they would be better off switching to something like 1075 or 1084? I was going to make a large knife that will likely see some abuse for a non knife-knut friend of mine out of 1095, but I'm starting to reconsider because I would much rather have the edge roll then chip and I don't want to compromise torsional strength.

I know what you're saying about ease of sharpening, some of my softer knives form a burr when you look at them funny.
 
Yes, there are better steels for that, using the high carbon steels and drawing them way down isn't the way to go about it, this is why other steels were developed instead of trying to make one steel do everything.

-Cliff
 
Well, ground thin enough, 52100 over RC60 makes a good inner core for specialized kitchen knives (often referred to as "Japanese" cooking knives).
 
Yeah, I've seen that--Ariel put one out not too long ago over in the custom knives section. How high can 52100 go before its toughness starts plummeting?
 
As 52100 isn't a tool steel, it isn't as easy to find the data on it as it is on O1 and similar steels. However given its similar composition I would expect it to have the same general behavior to its toughness curve.

-Cliff
 
I just sharpened a 1095 blade on the belt sander that was hardened using the same steps as the HRc 66 piece from a while back. The edge was uneven and took about 50 passes per side at p320 grit to even out and get sharp. I was careful not to let a burr form much, and the one that did was not flacid like foil. I then cut off the burr and polished with a leather belt covered with white buffing compound on the sander. I understand that CrO may be better, but I havent found any locally and I wont order any until my white stick runs out, or I have a large order from Lee Valley Tools. The edge cuts a hair held between the fingers without a draw, just a push. In retrospect, I may have overbuffed just a little. There were 3-4 small chips where the maker of the knife chopped through a 2x4. Its a 4" blade, 3/32 thick. I did not grind these out. Off to cut some more cardboard and see how the edge holds up. My previous record is ~1000 cuts on pizza box stock before it stopped cutting hair. The cuts were made with the same area of blade and were ~1" - 1.5" long. The knife was a Kershaw Random Task w/ S60V (CPM440V) steel, off the flats of the brown sharpmaker rods at 20 degrees. I know I have many variables unaccounted for, but if this homemade knife put together in 3-4 hours cuts as long or longer than the RT, I'll be really impressed. That thing held an edge like nothing before it that I've used, even cutting through some copper wire w/o problems.
 
I have a love/hate relationship with cardbord. On the one hand it tests many aspects of cutting ability and edge retention as it will both bind on a blade and deform and induce wear, but it is fairly difficult to get consistent results.

I have seen fairly dramatic swings in repeating runs, even when I do all the same cutting on cardboard from the same box and use jigs to set edges. I like to do 3-5 runs before being decently confident.

Results will be interesting, I think the Tasks were some of the 60 HRC S60V blades so that should set a decent benchmark. The true ability of the harder steels come at really low angles where the more coarse and softer steels break apart too easily.

-Cliff
 
Cliff Stamp said:
As 52100 isn't a tool steel, it isn't as easy to find the data on it as it is on O1 and similar steels.
Click to expand...

I'm pretty sure that L3 falls with 52100's faster and looser composition parameters.
 
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