Ray Kirk test blades in 1084, L6, 52100 and D2

History

These four test blades were supplied by Ray Kirk. The steels and hardness levels were unknown until after the testing was completed and reported to the maker. The blades were marked A,B,C,D . After the testing was completed, commentary was added to the review noting the influence of hardness and alloy type on the results. To ensure that the results were as free of bias as possible, before each round of testing, the letter markings were taped over and new markings applied by a friend.

These knives were hand made so some variance in profile is to be expected however the geometries were very close. The edge angles were checked in multiple places along the blades with a set of calipers. The knives made from 1084, L6, and 52100 were found to have edges ground to 13-14 degrees. The edge on the D2 blade was just under at 11-12 degrees per side. The edge thickness varied from about 0.015 to 0.025 from blade to blade, with a variance of about 0.05 along each blade. The edge geometry was also examined later by doing some stock cutting and measuring the force required and number of cuts, and the blades were within a few percent of each other.

Initial sharpness

The L6 blade was slightly rolled NIB, most likely due to an accidental contact so it was sharpened and honed to a fine shaving finish. All the other blades were very sharp NIB. To gauge edge retention sharpness was determined by push cutting light thread and slicing quarter inch poly under a fixed load. With the blades ready to begin the cutting :

The blades all push cut the thread well, and push shave very smoothly with no draw. The L6 blade was difficult to sharpen because of the low hardness and likely suffered from a small burr.

UPDATE : all blades should have been initially honed with the same abrasive, since the L6 was damaged all of them should have been rehoned.

Edge retention on used mats

Old mats were used as blunting stock, they are both very abrasive due to the grit and difficult to cut because of the thick rubber backing so both wear resistance and hardness are needed for high edge retention. Over a hundred mats were available and random sampling was used to ensure consistency.

round one

Four strips were cut off with each blade. Checking the edges under 10x magnification, the 1084 and L6 blade suffered extensive damage about 0.1 to 0.2 millimeters in size with 15-25 chips every 3 millimeters. The D2 and 52100 blade had just a few chips every 3 millimeters which were only 0.05 - 0.1 millimeters in size.

The thread and poly cutting were then used to gauge the extent of blunting. The edges were then aligned by steeling (5 strokes per side on a lightly grooved steel) and stropping (25 per side on canvas) and the poly cutting repeated. They were then further sharpened on a 600 grit DMT rod (two strokes per side) and again repeated the thread and poly cutting.

The push cutting edge retention :

After the mat cutting, all blades are dull and require about five times the amount of force to cut the thread, close to breaking it. The 52100 and D2 knives have a slight advantage which is more clearly seen after the sharpening, with the with 52100 a little better than the D2 knife. The 1084 and L6 blade are similar. improvement of at least 100%. the thread cutting after the alignment was intended to be done but was forgotten

The edge retention on the poly slicing :

As the blades were heavily dulled after the mat cutting, a very heavy load (7.5 lbs) was required. The 52100 and D2 blades are clearly ahead of the 1084 and L6 knives. No numbers need to be recorded to notice the difference, the aggression disparity is so large. After aligning, the slicing performance gain is about 350% with all blades. The 1084 and L6 make a slightly larger percentage gain than 52100 with the D2 blade being significantly behind. The 52100 knife is clearly ahead at this point. After the honing on the DMT rod the blades are all cutting very well again with the 52100 knife retaining a slight advantage.

commentary

On the thread, the better edge retention should be seen with the harder and higher alloy steels as they would better resist impaction and wear. This is indeed the case. After the aligning and steeling, the 52100 blade is slightly ahead of the D2 knife probably because it has a higher machinability. On the poly, the difference in performance is enhanced here and possibly shows the influence of the alloy carbides.

At this stage the 1084 blade and L6 blade performed very similar, it would be difficult to tell apart by feel. However the D2 and 52100 knives are a step above and could most of the testing be clearly ranked above the other two blades. The 52100 knife also responds faster than the D2 one in regards to alignment and on the abrasives which would be expected given its higher ductility and machinability.

round two

The with blades with the current edges, double the amount of mat cutting was done. During the cutting the D2 and 52100 had a slight advantage going by feel. After the mat cutting all of the blades were again very blunt, and just broke the thread. An even greater weight (10 lbs) needed to be used to enable the poly slicing.

After the mat cutting the 1084 and L6 blade are tore up in the first few millimeters (damage 0.1-0.2 millimeters in depth and width), but smooth after that. The D2 knife has many chips along the length, some as large as 0.2 millimeters in depth and width. The 52100 blade has more chips than the 1084 or L6 knife but less than the D2 one.

The blades were steeled (5 strokes), stropped on canvas (10 passes) and then leather loaded with CrO (5 passes), and then gave three strokes on a 600 grit DMT rod. The thread cutting and poly cutting (1000 g load)were again repeated. The DMT rod was then used again, 5 passes per side, and again the sharpness measured with the thread and poly cutting, (500 g load).

After the steeling and stropping and first work with the DMT rod, none of the blades could shave. The 52100 knife could cleanly slice through photocopy paper, the D2 knife was just a little behind, difficult to tell them apart. The 1084 Knife was significantly worse,leaving ragged edges, tearing the paper easily, the L6 blade. After the additional work with the DMT rod all blades will roughly shave.

The edge retention push cutting light thread :

After the light sharpening there is a clear separation between the 1084 and L6 knife compared to the D2 and 52100 blade. This correlates well with the results on the photocopy paper. After the second sharpening all blades are again at a similar level, with D2 having a very slight lead and L6 slightly behind.

The edge retention on the poly slicing :

The poly cutting showed the same grouping, just stronger. The 1084 blade was also slightly ahead of the L6 one and D2 edged out 52100. The additional sharpening on the DMT rod did little to D2 and 52100, they were already close to optimal level. All blades will now smoothly slice photocopy paper and will shave arm hair with a slicing motion.

commentary

The D2 blade is clearly more aggressive than the 52100 blade after the cutting, probably due to the large segregated carbides. The machinability makes a large influence here as the 1084 blade make the largest percentage increase after the light sharpening. The 1084 blade is also clearly outclassed by the D2 and 52100 blades, responds faster when sharpening and thus catches up. Similar issues are seen with D2 vs 52100. Since more force is starting to be used on the cuts here, impact toughness starts to come into play and the D2 blade will start to experience a little more edge fracture than the tougher 52100 knife.

round three

With the existing edges, this time triple the amount of first round work was done. During this round the L6 knife blunted significantly faster and was definitely behind the other blades. The difference could be readily ranked by feel.

After the cutting the 1084 and L6 knife had chips about 0.1 millimeters in size, but infrequent, less than 1 per 3 millimeters. The D2 blade had more chips about 2-3 times as frequent but of similar size. 52100 was better than the D2 blade but worse than the other two. Again the 10 lbs weight was used for the poly cutting with the blades in the heavily dulled state.

The knives were steeled (5 per side) and stropped on canvas (10 per side) which made a large difference, all edges would catch on the thumbnail, but none were close to shaving nor could cut through the poly on a 1000 g load without multiple passes along the blade. They were lightly honed on the DMT rod (3 per side) and then cut the poly under a 1000 g load. A further honing on the DMT rod (10 per side) and the cutting was repeated with the same load. An attempt was made at 500 g, but the L6 knife would not cut it well enough.

All blades busted the thread after the mat cutting, and only became able to cut it after a light sharpening (steeling five strokes per side, stropping 10 strokes on canvas, finally three strokes on 600 grit DMT rod). L6 was much blunter and kept busting the thread right up to the end. The thread results :

The same rank is found as before, just with larger differences. A similar rank is seen on the poly cutting :

Here D2 clearly has an advantage over 52100 in both the dulled state and after the light honing. Both are identical after the final honing. L6 is now clearly behind the other blades and was left out of further work.

commentary

Here the L6 blade is so far behind due to the excessive wear and impaction/distortion that even though it responds well to sharpening, it never catches up. The 1084 blade is far ahead of the L6 blade, showing clearly what a six point difference in Rockwell makes, and the high alloy steels are a grade ahead again. This time there is a clear difference in the D2 blades performance as compared to the others, it stands out distinctly as the leader.

With more force being required to cut the mats, the D2 blade is now clearly suffering edge damage due to toughness problems. The 52100 blade suffers some slight edge damage, it fares better than D2 but not as well as the 1084 and L6 blade, which you would expect given the relative impact toughness and ductilities.

This round clearly shows the out classing of the softer L6 blade. The alloy blades (D2, 52100) are also a clear step about the 1084 knife. It is also the first round in which the greater response to sharpening doesn't make up for the excessive blunting in the 1084 blade and especially the L6 knife. However after sharpening the 52100 blade can hold its own with the D2 one.

round four

As a final round, four times the amount of cutting was performed as done in the initial session. During the cutting the 1084 knife quickly became less aggressive, similar to the behavior of the L6 knife in the previous round. After the cutting the D2 knife had chips about 0.1 millimeters in size about one per every three millimeters, the 52100 knife was similar and the 1084 blade was a bit better.

The blades were steeled, stropped on canvas, then lightly sharpened on the DMT rod (5,10, 3 strokes per side respectively). All failed to cut the cord under a load of 1000 g and even 1500 g. The blade were then sharpened again on the DMT rod, 3 strokes per side. Now only the 1084 knife was unable to cut the cord, the other two knives were very similar. After another three passes on the DMT rod, they were all once again at the initial level.

commentary

Here the difference between the 1084 and alloy blades (D2 and 52100) was more clear. The 1084 blade blunted so rapidly that it became difficult to finish the mat cutting. Even after a light sharpening the 1084 blade can not cut the poly, many times blunter than the D2 and 52100 knives and even after the more extensive sharpening it is still about 50% behind. However the fact that it makes such a dramatic increase shows how quickly it responds to aligning and abrasives. The D2 and 52100 blade as pretty much dead equal in this round. it has lost its main advantage over the 52100 blade.

Overall

It is clear that the drop in RC of the L6 blade gave it a huge disadvantage. It was also clear that the alloy steels had a significant advantage over the plain carbon one, much larger than a one point in RC would make, and that the higher carbon and higher alloy D2 blade out-lasted the 52100 one. It is also clear that pretty much the exact opposite was observed in regards to response to sharpening. This tended to balance out the performance somewhat, but not enough to overcome the advantage in wear resistance due to the alloy carbides, and greater percentage of said carbides for D2 over 52100.

In regards to toughness, while the L6 and 1084 blades do suffer less fracture under the heavy cutting, they suffer so much wear that in the end they are in a more degraded state than the more brittle alloy steels. The comparison between D2 and 52100 goes much the same way. 52100 does resist chipping better, which is no surprise, but it suffer so much more wear that the overall state of the D2 edge is of high quality. The work also shows how how slicing and push cutting are not effected in the exact same manner as a blade blunts. The carbide nature of the hard alloy steels gives them a very large advantage in regards to slicing. They also are ahead in push cutting, but not to the same degree.

Note during the final round, 2000 cuts per round were made into the mats and the load required was quite high as the mats had a heavy tight carpet weave with a thick rubber underlay. The load on average was ~100 lbs towards the end. Considering all the cuts done over the four rounds, ~500 000 lbs of force was exerted. This took some time to do.

Bone cutting

Each blade was used to section six chicken wings. A cut was made to remove the tip and one to separate the wing, twelve cuts in all with each knife. Five cuts were made clean through the joint, minimal bone contact, minimal force. Five cuts were made in a sloppy manner through the joint, ~50 lbs of force. Two cuts were made behind the joint, right through the bone, ~100 lbs of force required.

After the cutting no blade had visible damage. The L6 knife fared the worse, it had only about two centimeters of clear edge under light, the rest reflected light strongly. The 1084 knife had some light reflection along the belly. The 52100 blade had some light reflecting, a reduced amount than the 1084 knife. The D2's edge was crisp, no reflection.

This performance would be expected based on hardness. To check that it is just distortion and now wear, a lightly grooved steel was used on the L6 blade, two dozen strokes per side. The Razor's-Edge smooth steel was then used, again two dozen strokes per side. Only 0.5 millimeter long distortions remain. The knife was now just under hair scraping sharp.

Concrete cutting

As a test of durability in extreme circumstances, the knives were used to whittle a concrete block, twenty hard slices were made across the edge. The performance details :

1084 : 56 RC

• one ~0.2 millimeter deep dent/fracture
• eight 0.1 to 0.2 millimeter deep dent/fractures
• several shallow dents/ripples 0.05 millimeters deep, but ~2 millimeters long

L6 : 50 RC

• one ~0.3+ millimeter deep dent/fracture
• seven 0.1 to 0.2 millimeter deep dent/fractures
• no ripples
• overall a lower frequency of damage than the 1084 knife

D2 : 57 RC

• two ~0.2 millimeter deep dent/fractures
• six 0.1 to 0.2 millimeter deep dent/fractures
• several shallow dents/ripples 0.05 millimeters deep, ~2 millimeters long, similar to the 1084 blade

52100 : 57 RC

• six 0.1 to 0.2 millimeters deep dent/fractures
• no large chips or ripples

The results here depend not only on hardness but also ductility and impact toughness. Comments

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 one part of the edge should have been left untouched so as to gauge the amount of material worn away. The lower overall number of damaged areas could be due to wear.

1084 : 56 RC

• With the higher RC this blade resists indentation stronger than the L6 blade, no 0.3 millimeters+ deep damage. However it is not quite as tough nor as ductile and sees a higher frequency of damage. The large ripples are possibly due to fracturing, a combination of high impact shock and significant distortion.

D2 : 57 RC

• This blade sees a greater number of 0.2 millimeters deep damaged areas than the 1084 blade due to its lower toughness. The ripples are probably stress fractures due to the low ductility.

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 millimeters 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.

As a check for wear and damage, the times for sharpening (220 grit SiC waterstone ) was noted .

With minimal and high machinability the 52100 blade gets refinished first, the 1084 blade is close behind. Even though the 1084 knife took more extensive damage, it has a higher machinability. The D2 blade will respond slowest to the hone, but also suffered the least wear due to the high alloy carbides. The L6 blade was much more heavily abraded by the concrete and required much more honing time.

All the blades were then polished on a Sharpmaker the ten passes on a CrO loaded strop and then ten on plain leather. All would now push shaving easily and scored very highly on the thread and poly cutting :

Comments and references

You can comment on this review by dropping me an email : cliffstamp[REMOVE]@cutleryscience.com or by posting in the following thread on Bladeforums :

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

Ray Kirk also has a web page which has more information on his knives. He has also come in first place at multiple cutting contests.