Edge testing on 1084, L6, 52100 and D2 blades supplied by Ray Kirk

As a last test on edge retention and durability I did about the hardest cutting possible, twenty hard slices across the edge of a concrete block attempting to "whittle" pieces off. The edges had to deal with a very abrasive material plus very high impact collisions off of the rocks. The state of the edges after the cutting :

A (1084 / 56 RC) :

-one ~0.2 mm deep dent/fracture
-eight 0.1 > 0.2 mm deep dent/fractures
-several shallow dents/ripples 0.05 mm deep, but ~2 mm long

B (L6 / 50 RC) :

-one ~0.3+ mm deep dent/fracture
-seven 0.1 > 0.2 mm deep dent/fractures
-no ripples
-overall a lower frequency of damage than A

C (D2 / 57 RC) :

-two ~0.2 mm deep dent/fractures
-six 0.1 > 0.2 mm deep dent/fractures
-several shallow dents/ripples 0.05 mm deep, but ~2 mm long, similar to A

D (52100 / 57 RC) :

-six 0.1 > 0.2 mm deep dent/fractures
-no large chips or ripples

The results are not as straight forward to interpret as the previous work as the condition of the edges depends strongly on multiple factors; wear resistance, hardness, strength, ductility and impact toughness. Anyway :


B (L6 / 50 RC) :

-Given the low RC it is expected that it would see the deepest damage due to a high impaction. It is also understandable that the overall frequency of small damage (fractures) would be lower than the 1084 blade as the L6 one would be tougher both due to the inherent nature of the steel and the lower RC. In retrospect I should have left one part of the edge untouched by the concrete so I could gauge the amount of material worn away, more on that later. The lower overall number of damaged areas could simply be that the very low wear resistance is causing the steel to be worn smooth.

A (1084 / 56 RC) :

-With the higher RC this blade resists indentation stronger than the L6 blade and thus it doesn't have any 0.3 mm deep damage. However it is not quite as tough nor as ductile and sees a higher frequency of damage. The large ripples I think are due to fracturing, a combination of high impact shock and significant distortion, I have seem similar damage before on very hard cutting.

C (D2 / 57 RC) :

-This blade sees a greater number of 0.2 mm deep damaged areas than the 1084 blade which makes sense as it has a lower toughness so it should fracture easier. The ripples are probably stress fractures due to the low ductility.

D (52100 / 57 RC) :

-This blade has the optimal level of hardness, toughness and wear resistance to minimize the damage. It takes some small ~0.1 mm indents/fractures, but no large ones, nor any large ripples. It has enough strength and impaction resistance to prevent any excessive dents or rolls, and at the same time has enough impact toughness to prevent excessive fracturing.

Checking for wear and damage I noted the time it to to reshape the edges on a 220 grit SiC waterstone :

D (52100 / 57 RC) : 7.46 min
A (1084 / 56 RC) : 8.15 min
C (D2 / 57 RC) : 9.40 min
B (L6 / 50 RC) : 17.02 min

Thus with the minimal damage the 52100 blade gets refinished first. The 1084 blade is close behind as even though it took more extensive damage, it will be abraded quicker by the hone and thus catch up. The D2 blade will respond slowest to the hone, but since it suffered the least wear due to the high percentage of Cr carbides, it doesn't have far to go. The L6 blade was much more heavily abraded by the concrete, I could tell during the sharpening that much more work had to be done on it even without checking the time.

All the blades were then polished on a friends Sharpmaker, and then given ten passes on a CrO loaded strop and then ten on plain leather. All blades were now push shaving sharp however I could just barely notice a small relative drop in performance of the L6 blade, it was not quite at the same level of screaming sharp. Checking the performance on thread :

D2 : 108 +/- 2 g
52100 : 108 +/- 9 g
1084 : 107 +/- 7 g
L6 : 118 +/- 10 g

So yes the L6 blade is about 10% behind, this may be just the edge rolling just a little more on the Sharpmaker, a common problem with soft blades. Checking for slicing aggression on 1/4" poly, the L6 blade was again just barely behind :

D2 : 5.0 +/- 0.8 mm
52100 : 4.8 +/- 0.9 mm
1084 : 4.8 +/- 11 mm
L6 : 5.7 +/- 0.5 mm

Some general comments on the steels (assuming similar RC, ~ 57) for small knives :

1084 :

-A plain carbon steel, very little wear resistance due to the total lack of alloy carbides. Very good toughness so it will resist chipping well. Thus it will have low edge retention in abrasive work as the edge will quickly be worn away. However good edge retention in high impact work as the edge will resist chipping well. Will sharpen very quickly even on soft hones, about the easiest there is to work.

L6 :

-Tougher than 1084 with a little more wear resistance. A slightly refined grain structure as well. It will resist wear just a little better than 1084 and be even tougher so over all will have better edge holding. It will be just a little harder to sharpen, but due to the low alloy content, this will not really be noticed unless you are timing the sharpening. The greater edge holding will counteract this anyway.

D2 :

-A steel designed to run in pretty much the opposite direction in regards to performance. It has a very high wear resistance, among the top of the tool steels, do to the high percentage of Cr carbides as well as the small amount of Vanadium. At the same level of edge distortion as a low alloy steel, D2 will have an increased slicing ability do to the aggressive nature of its carbide structure. However for much the same reason that it resists wear well and makes a great high performing cutting blade, it suffers from a low impact toughness and will see chipping much more frequent than a lower alloy steel. It is optimal for a light use cutting blade.

52100 :

-While this steel does not have anywhere near the wear resistance of D2, it does have a much higher toughness and thus in many cases it can give very close edge retention and cutting aggression. It will also sharpen faster and thus it tends to catch up rapidly as it is honed even though it would see more wear. The other tougher steels (1084 and L6), don't offer a significant advantage for smaller knives because of the low weight and small blade length, 52100, when heat treated well, is easily tough enough for even the worst cutting. Toughness is a step property in materials, which means that basically once you have enough, you don't gain anything by having more. Thus it is not as good as D2 for light use, but has a much broader range of usage because of the greater toughness and ductility. It also doesn't need an aggressive a sharpening medium as D2.

In regard to corrosion resistance, 1084 and L6 will take a patina very rapidly, you can almost see it happening if you use them on acidic foods. Plain carbon steels however don't tend to pit extensively, long term soaks in salt water on 1095 blades just resulted in surface corrosion. D2 will resist mild environments much better, but when soaked in salt water will develop very deep pits, as will ATS-34, VG-10 etc., and other similar stainless steels. 52100 seems to be very similar to 1084 and L6 in terms of taking a patina, I have not done any salt water soaks on it as of yet.

As for larger blades, there would be a much larger difference seen in regards to edge durability. In chopping blades impact toughness and ductility play a very large part in edge retention and thus very tough and ductile steels can actually move ahead of highly wear resistance ones like D2 in regards to edge retention as if the edge is breaking apart, having a great wear resistance only means that it will take longer to remove the chips.

Note to clarify ease of sharpening, even after the last round of mat cutting which was quite extensive and blunted the blades down to about 10% of their optimal level on quarter inch poly (which is quite blunt), the blades were restored back to optimal with only nine passes per side on a DMT rod. In general it takes very little to restore knives assuming that the abrasive is of high quality and is not in a highly loaded state. If I had not being using such an aggressive sharpener, the D2 blade would have seen a loss in response to sharpening because of the high carbide content. However Diamond hones will cut even the hardest and highest alloy steels like butter.

In regards to D2 at 60-61RC, that is an excellent question. It is obvious that it would have a much higher resistance to wear and rolling, however its impact toughness and ductility would be pretty much nonexistant. The critical question is would the edge durability be enough to allow the wear resistance and strength to be an advantage or would the edge just break apart under the strain? I have a D2 blade at 62 RC, I'll see if I can't do some of the above cutting with it and give a less vague answer, it is an interesting question and hits at one of the central goals of heat treating for blades.

Thanks all.

-Cliff
 
Thanks for the additional conclusions. Bob Dozier heats his blades at 60-61RC. I have used one of his folders extensively as a side companion to my commercial carpentry work. I have not attempted to cut concrete(!), however, I have used the knife on many materials that are fairly abrading: Fiberglass batting, FRP (fiberglass reinforced plastic), fiberglass reinforced poly, framing woods, hard woods and so forth. Mr. Dozier also recommends using diamond abrasives for resharpening his knives. At this moment in time, I have not found a blade that will out-perform the D2. I would like to try out a folder with 52100, now, though. Considering your test 52100 blade, what do you suppose an optimal RC would be in a folder 3 to 4" long?
Again, thank for the interesting study.
Barry H
 
Barry :

Bob Dozier heats his blades at 60-61RC.

That is about the limit hardness for D2 and you can expect very strong edge retention obviously. This is also enhanced by the high cutting ability due to the high primary hollow grind which also makes sharpening very easy. In all a very fine package which is obvious to those who have used his work.

I have used the knife on many materials that are fairly abrading: Fiberglass batting, FRP (fiberglass reinforced plastic), fiberglass reinforced poly, framing woods, hard woods and so forth.

Fiberglass insulation is wonderful material to use as blade testing medium if you can stand being around it. As for use in general, when I really want to give one of my knives a heavy run over I will lend it to friends who do construction work. It doesn't sound as impressive as being used by a Navel Seal, however the knives get used to cut just about everything and anything and if you give the go ahead for a "utility" perspective they will be hammer with an on, used as screwdrivers, pry-bars etc. .

Mr. Dozier also recommends using diamond abrasives for resharpening his knives.

Yes, a high carbide percentage, especially with the Vanadium in D2 is not one that will be easily dealt with by soft hones. Using quality and clean diamond abrasives however it is easily honed.

At this moment in time, I have not found a blade that will out-perform the D2.

In regards to edge retention in common steels there is not much that will give any competition, basically you are left with M2 and it better be ran hard. M2 at 58-59 RC is not going to out last D2 at 60-61 RC. Another option would be BG-42 at 62-64RC and CPM-S90V at 61-63 RC. Get a full cryo on these if at all possible, if not make sure that triple tempers are used to ensure full austenite transformation and optimal grain refinement.

I would like to try out a folder with 52100, now, though. Considering your test 52100 blade, what do you suppose an optimal RC would be in a folder 3 to 4" long?

52100 is not going to offer better edge retention than D2, however what it does offer, due to its inherent greater toughness, is the ability to be used a little rougher, or from another perspective the ability to be ran in edge geometries that are a little thinner and thus have a higher cutting ability. I would get the 52100 up to about 60 RC assuming you don't want it to cut hard materials like concrete, anything else is not going to bother it much at all. Here are some comments on a 52100 blade which has an edge hardness of 57-59 RC, and even wood splitting through knots didn't bother it :

http://www.physics.mun.ca/~sstamp/knives/MEUK_52100.html

And another of Ray's 52100 knives, which suffered only minor damage even on worse case uses :

http://www.physics.mun.ca/~sstamp/knives/bowie_ray_kirk.html

Again with the 52100, get a full cryo if you can, make sure there is a post temper obviously. If there is no cryo make sure it is triple tempered. The edge geometry is the critical thing, for the uses you outlined in the above there is no need to go above 0.01" in thickness behind the edge and even thinner is possible. Ed's 52100 blade is only about 0.005" thick behind the bevel, just basically visible. He also makes folders now so you might want to drop him a line, and will do deep cryo on the blades.


-Cliff
 
Thanks for the comments, Cliff. What can you tell me about Steve Dunn and his methods of heat treating? I have not had much luck finding info on his work.
Thanks,
Barry H
 
Steve Dunn is a Master Smith in the American Blade Society and has helped me out a few times with information and techniques in making knives. He does outstanding work and is a reliable person to deal with. You can't go wrong with one of his knives.
He also works with 52100 and does his own damascus. Fixed or folders, Steve does them both.
 
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