Cliff Stamp
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- Oct 5, 1998
- Messages
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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
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
