Edge aggression on a slice as influenced by finish and angle

[Cliff Stamp]

Joe Talmadge and Mike Swaim were two proponents of edge thinning and low grit finishes for high slicing ability on rec.knives. One thing I noticed when playing with both is how they act to increase each other strongly. The reason why will be obvious as soon as it is pointed out, however it never came to me until I saw it under magnification, just never thought about how they would interact when combined.

When you reduce the edge angle, you reduce the amount of force that it takes to push the blade through the material, thus the cutting ability goes up in a fairly linear manner with angle. In a similar way, when you keep the angle constant, and reduce the finish, the deeper teeth increase the amount of material cut on a given slice, also in a linear manner.

However when you do both at the same time the result is a lot more than you might expect. What happens is that the thinner the edge, the deeper the teeth that will be produced by a given finish. This means that you will get more aggression on the slice compounded on top of itself. This means that you can see some extreme effects if you say go from 20 -> 15 degrees while going from 1200 - 600 grit.

What is often overlooked, is that the edge retention increases right alongside with the cutting ability. The deeper teeth mean that more metal has to be worn away in order for the edge to smooth out, and that deformation has to take place to a larger degree in order for the teeth to fall out of alignment completely (the cut tracks don't overlap).

As an extreme high end case, I have a D2 blade (62 RC, Mel Sorg), with an edge at ~5 degrees per side, 100 grit AO finish, full flat/convex grind on 3/32" stock. After 2046 slices (2" draw) through 3/8" hemp, the blade can still make the cut with ~20 lbs, *and* can still vertically slice newsprint. Checking the edge under magnification, there was no visible degredation through the last 1024 cuts, due to the high alloy percentage of D2, the edge is probably all carbide now. On the other side of the spectrum, a SOG SEAL, with a much thicker edge (5x the angle), softer steel (440A, RC in the fifties), after ~14 cuts with a 600 DMT finish is blunted to a much greater degree, can't slice newsprint at all (piles more numbers for those interested).

As a complication, the edge retention can decrease if you go too far with the angle, however I have not found that to be the case when cutting normal materials like rope and woods and such, however whittling on very hard woods, plastics and the like can visibly roll ultra thin edges and the cutting ability will be gutted as Chad noted awhile ago with low angles on Opinels. You can solve this problem by using a secondary micro-bevel of width approx. the same extent as the rolling that was induced. For chopping this is a very important consideration as if you go too far you will induce visible edge rippling or blow outs.

-Cliff

 

[Joe Talmadge]

Good stuff Cliff. One of the things I've always been a little puzzled about is how people always say that the thinner edge gives less edge retention but better cutting performance. I felt that sometimes the thinner edge did lose effectiveness more quickly, but, sometimes an edge I'd just thinned would actually cut effectively longer than a thicker edge. Why then were so many people on the net convinced that thinning the edge would always result in less edge retention?

Though I hadn't actually tested it closely and looked under magnification, I guessed that there were two things at play:

• The thicker edge starts out performing worse than the thinner edge, so even if the thinner edge wears more quickly, it has to lose a lot of metal to even reach the point where its performance has degraded to where the thick edge started at.
• The thinner edge is definitely more susceptible to rolling and chipping, so the more edge stress in the particular cutting job, the more likely the thinner edge would lose its cutting ability quickly

I tend to leave my edges with a coarse grit -- not to be too glib, but it's more important to me that they cut materials well, than cutting my arm hair well -- so I've probably been seeing some of what you're noticing.

 

[chad234]

I had not realized that the effect was as exponential as the Sorg v. Seal blade indicates. Good stuff.
I agree that it is a matter of what your intended goal is. IF you are slicing lots of rope, a course edge is great. If youare push cutting through hard plastics you'll likely see rapid edge degradation, both from rolling as you guys have indicated, but also from tearouts. While a torn out edge is even more aggressive you lose cutting ability becasue of the shifts in edge alignment it causes. For wood work, the very highest levels of polish are desired.
THis week I was using a Full size VG10 Calypso to break down cardboard boxes. The edge is under 25 degrees included and was at a DMT X-course (black) finish. Talk about aggression, I would put that knife against a fully serrated knife (my Endura for example) in rope cutting anytime. A huge advantage of a course plain edge is that it does not snag when cutting fabric; as a serrated edge is prone to and the plain edge can still pushcut well. The knife can be optimized for a number of tasks with just a few minutes of edge polishing (or making it more course, even faster).
That being said, for a single do it all edge finish I find it hard to beat a medium ceramic, like spyderco brown stones. In the alternative I often use an ezlap fine diamond bench stone (which is more agrressive than the cermic medium).

 

[Cliff Stamp]

Joe :

Why then were so many people on the net convinced that thinning the edge would always result in less edge retention?

This is one of the common knife "myths", it is similar to the claim that the sharper the knife, the less durable the edge. If I had to guess, I would say that the main reason for both of these claims are the rise in popularity of the brittle high carbon stainless steels combined with the surge in "tactical" promotion, which forced a radical chance in edge geometry, which had to be defended without degrading the steel.

The thicker edge starts out performing worse than the thinner edge, so even if the thinner edge wears more quickly, it has to lose a lot of metal to even reach the point where its performance has degraded to where the thick edge started at.

Yes, quite true, and since blunting is logarthmic, you will thus gain edge retention rapidly with a thinner edge. To be a bit more clear, you don't actually effect edge retention at all in most cases, just simply, as you argue, the higher inherent cutting ability means that more edge degredation has to take place - so the edge lifetime has increased. Getting even more specific, blunting will happen at the same rate regardless of edge angle for most materials (except in extreme cases where the structural stability of the edge has been exceed).

For example if you take a knife at 20 degrees per side at a particular finish, and watch how the force increases as you cut rope (or anything similar), and then repeat it with the same blade at 15 degrees per side, you will see that the force increments are the same. Since the 15 degree blade starts off needing a much lower load (15/20 roughly), it will have to cut *far* more rope than the more obtuse edge has to, in order to reach any set stopping point.

The thinner edge is definitely more susceptible to rolling and chipping, so the more edge stress in the particular cutting job, the more likely the thinner edge would lose its cutting ability quickly

Yes, however, as Chad commented in the Wilderness forum on Knifeforums, while you do lose strength quite rapidly with edge thinning, you are also required to use a lot less force when doing the cutting, thus the edge is far less likely to see high lateral loads from twisting or other loss of control. Problems set in when you are cutting very difficult materials like wire, bone or particle board. These materials have the ability to directly impact the edge, and/or have very high probabilities of inducing lateral loads. Secondary micro-bevels are the way to go here, such as the double beveling you have described with the Sharpmaker.

Chad :

If you are push cutting through hard plastics you'll likely see rapid edge degradation, both from rolling as you guys have indicated, but also from tearouts. While a torn out edge is even more aggressive you lose cutting ability becasue of the shifts in edge alignment it causes.

Yes, I have looked at this a little, enough to know that it is a factor, I have not in any detail though. Essentially you just go to a high polish for such work, as you are mainly push cutting anyway, so its not a weakness I am that interested in, though for many it could be critical. It is obviously something that you do need to be aware of. For example, awhile ago I was shaping some hard plastic with a Sub-Sniper (Griffith), of which I have drastically lowered the edge profile. I snapped off a small piece of the point (0.5 mm), and did break out a little piece of the edge, twisting it in the plastic. Wrong knife for that work, excellent for light utility cutting in general though with the current profile. Would have not been effected at all on the plastic with the NIB profile.

For wood work, the very highest levels of polish are desired.

Yes, this is mainly push cuts, high and low impacts. It was well known a generation or so ago, but now it seems common perspective that a "rough" edge is best, especially for chopping. Lee presents clear evidence of otherwise in his sharpening book, and gives references to where it has been studied in more detail. It can also be shown from just a very basic argument as higher polishes eliminate structural weaknesses. A complication arises when you are chopping as the main blunting effect, but testing sharpness by slicing - now you need an edge finish inbetween.

A huge advantage of a course plain edge is that it does not snag when cutting fabric; as a serrated edge is prone to and the plain edge can still pushcut well.

Yes, there are lots of different serrations though with lots of different behaviours. At an extreme you have the ones with the very sharp and pointy patterns, such as SOG used on the SEAL. These have a very low cutting ability in general and can't do much but tear. However they are, for the same reason, able to handle some very abusive tasks such as cutting on steel, ceramic plates etc., with minimal impact on the cutting ability. On the other side of the spectrum are the rounded, convex scallops used by Mission. These are much more fluid, don't catch, and can actually push cut well. They don't have quite the extreme durablity of the SOG type serrations in very abusive cutting, but are much more durable than a plain edge for most cases.

The knife can be optimized for a number of tasks with just a few minutes of edge polishing (or making it more course, even faster).

Yes, this is the first time I have seen this pointed out, the versatility is well known, but if you carry some sharpening equipment with you, a few passes to set a micro bevel can have you from a very fine polish, to a very coarse finish (and back again), in just seconds.

... for a single do it all edge finish I find it hard to beat a medium ceramic, like spyderco brown stones. In the alternative I often use an ezlap fine diamond bench stone (which is more agrressive than the cermic medium).

As of late I have been radically lowering the edge profiles of my knives, they are now about half of what they were a year ago, and are now at the limit of what can be achieved with convex and flat grinds since they are basically puukko style. I have found now that even with a very fine finish, they still slice aggressively for most materials. This will be even more true when I get a wet wheel grinder and hollow out the blades to get even more edge relief.

I have been discussing this with Alvin and rec.knives and has referred to profiles that are *much* more thinner (0.008" a 1/4" behind the edge) than what I have been using so there is a ways to go yet, which is nice. For rougher work, I carry "utility" class blades. These are knives that get passed to friends, as well as for personal use on dirty materials, Rucksack + Supertool, plus a high-end prybar class knife usually, currently a TAC-11.

-Cliff

 

[mschwoeb]

One company that I know of has moved to edges that are thinner, though not as thin as 5 degrees per side. Buck Knives modified its edge angle with its edge 2000. They did testing and found that like you say, it cuts better, and actually last longer. And this is with 420HC.

 

[chad234]

A co-worker bought a Buck 2000 edged knife. IT has a chisel edge (though the primary grind is double hollow ground)and a coating that extends to the flat (unground)edge.
He bought it last year, and stated that he cleaned 5 deer with it, it was still shaving sharp. He brought it to me to touch up the edge, the spyderco 20 degree angle in fine ceramic had the edge stunningly sharp. Becasue it is chisel ground that 20 degree angle is the total edge angle, which is quite acute, extremely so for a production knife.
However, being chisel ground does lead to other performance issues, ie streying on straight cuts.
While he is very happy with it, it is not something I would buy.

Cliff:

Yes, however, as Chad commented in the Wilderness forum on Knifeforums, while you do lose strength quite rapidly with edge thinning, you are also required to use a lot less force when doing the cutting, thus the edge is far less likely to see high lateral loads from twisting or other loss of control.

This is what I have observed, but it seems counter intuative. I have thinned down edges, and seen no loss in "usable" durability because the increased cutting performance directly leads to the use of less force and better technique. However, as you have noted, loss in cross section results in a quadratic loss in strength. Therefore, I would expect to see damage in the thinner edges.
The only explanation that I can come up with is that sloppy technique and the extra force required of a thicker edge increases the stress on the edge to a greater degree than the quadratic loss that results from thinning.

As of late I have been radically lowering the edge profiles of my knives, they are now about half of what they were a year ago, and are now at the limit of what can be achieved with convex and flat grinds since they are basically puukko style. I have found now that even with a very fine finish, they still slice aggressively for most materials.

Much of my work is with Scandanavian knives with single edge bevels. If I want excellent slicing ability I polish the entires edge bevel to a high level (charged strop), the go over just the edge at a slightly more obtuse angle with an extra course diamond hone.
I do the same with my SAKs, I keep them at a high polish for pushcutting, but if rope needs to be cut, a few swipes on a EZlap type S hone (the size of an ink pen and weighs nearly nothing) that I keep in my uniform blouse pocket, and the slicing ability is very high.

A knife that is high on my interest list is the Rosseli Ultra high Carbon Carpenters knife, a small fixed blade with a hardness of 64-66 IIRC. Looks great.

One last point, yesterday I was clearing some weeds and grasses from my preoperty with a USGI machete. I started with a highly polished edge, which worked very well on the grasses. As i started into the briars, I found that a filed edge (using a martindale file) actually worked better on pencil sized stuff.
Just the oppisite of the performance I expected to see?????

Chad

 

[Barry H]

Thanks for all the input. As a professional woodworker, as a matter of habit, I usually double bevel all my chisels. Sure seems like the chisels stay sharper longer. Especially if I am working maple.
As for my work knives, I have been thinning my edges from the original starting point. I have found that the different blade styles (and thicknesses) have a big factor on what I am trying to do. My Strider S30V AR sure can take alot more punishment at 40 degrees compound than my S30V Sebenza, also at 40 degrees. Two different profiles, two different performance ratios. I'll take my Sebenza in the kitchen anyday over my AR.
I would be interested in taking a look at the Rosseli Carpenter knife.
Any links?
Thanks,
Barry H

 

[Jimbo]

For moose quarter skinning and such a lot of old timers would only use an old thin bladed knife sharpened with the finest file they could find. It works surprisingly well. I'm sure Alberta Ed can fill us in on this one..

 

[matthew rapaport]

Although a thin edge cuts better, and may last longer than a thicker one because it takes less force to make the cut, it also turns the knife into a more specialized tool.

Lateral loads on an edge are a fact of life in the field. The problem is made worse by a fatigued user who, while he/she may have been careful about lateral force when fresh and feeling strong, becomes much sloppier as he/she gets tired. There are also applications that lend themselves to lateral stresses. I've known of hunters who use scalpel sharp knives to field dress their game and then use the same knife with a baton to blaze a marker on a tree! If you are going to carry a very thin-edged knife for its slicing ability where you can apply the edge carefully, you should take something else with a more robust edge for everything else.

 

[chad234]

Matthew,
I agree with everything you wrote, but with a twist. I am very much in favor of turning knives into specialized tools. By having your blades optimized for certain tasks, and then carrying an assortment of tools to cover you most widely encouneted tasks, you can accomplish chores in the most efficient manner.
The one knife does it all is just not for me. I want high cutting performance, first and foresmost. Veristlity can be important, but I have my choice of tools, so I take care in selecting the proper one for the job.
That being said, right now I am only carrying one knife on the average day, a SAK though when I leave the house I add a folder IWB. With summer here, and 90 degree days with 99% humidity I am wearing the lightest clothing possible.

Take care,
Chad

 

[Joe Talmadge]

Originally posted by Barry H
I have found that the different blade styles (and thicknesses) have a big factor on what I am trying to do. My Strider S30V AR sure can take alot more punishment at 40 degrees compound than my S30V Sebenza, also at 40 degrees.

Barry, could this be a result of the Strider's S30V being (I'm guessing) 3-4 Rc points harder than the Sebenza's?

Joe

 

[Barry H]

True enough, Joe. But the AR has a flat ground blade, and the Sebenza is hollow ground. The Sebenza has a thinner blade, too.

A couple of weeks ago, I was cleaning off some very old paint on some yellow pine with the Sebenza. When I got home in the evening, I noticed when I was touching up the blade, the edge chipped out in a couple of spots. I was suprised because the RC is quite a bit lower than some of the custom guys, and I thought the edge would have been more forgiving before chipping out. Now maybe there was some wierd debris embedded in the paint, or maybe I hit a knot. But, I have since repeated the same task with the AR many, many times, with no degradation to the edge. I guess I chalked it up to my impression that the AR's edge is stronger due to the flat
grind.

Whadday think, Joe?

Barry H

 

[Cliff Stamp]

mschwoeb :

Buck Knives modified its edge angle with its edge 2000. They did testing and found that like you say, it cuts better, and actually last longer. And this is with 420HC.

Yes, they also made public the CATRA data which showed how the 420HC blade at a more acute angle outcut, in both raw performance and edge retention, blades with much higher end steels. Spyderco also runs most of their folders at 15 degrees per side, which is far more acute than for example Benchmade.

chad :

Becasue it is chisel ground that 20 degree angle is the total edge angle, which is quite acute, extremely so for a production knife.

This is the primary reason why people promote high levels of cutting ability for chisel ground knives, they simply have a low included angle. Steve Harvey made the same point about most serration patterns.

... sloppy technique and the extra force required of a thicker edge increases the stress on the edge to a greater degree than the quadratic loss that results from thinning.

This would imply that the edge would get more durable as you thin it, and in fact I have seen this happen (Machax from Camillus), for exactly the reasons you describe. For any cutting, all that is required is that durability not be under the functional limit for the specific cutting task, and for most materials, with proper method, this is a very low limit. It usually takes extreme cases of cutting to see the functional advantage of the NIB thicker profiles. For example I had a bad glance with the 5 star Arkiva with the NIB profile and it did little but impact the edge. After I thinned it out significantly, it suffered no durability loss in wood working ability, however a similar glance into a rock took out a large piece of the edge :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=200354

A knife that is high on my interest list is the Rosseli Ultra high Carbon Carpenters knife, a small fixed blade with a hardness of 64-66 IIRC.

Yes, that caught my eye as well, as have Murray Carters laminated blades.

[USGI machete]

... a highly polished edge, which worked very well on the grasses. As i started into the briars, I found that a filed edge (using a martindale file) actually worked better on pencil sized stuff.

I have been doing a lot of grass cutting as of late with blades, mainly as I had never done a lot of it, instead I mainly do wood working as grass doesn't give a lot of heat in a wood stove. In short, I have found, thas as with any cutting which doesn't induce a wedging action, sharpness is the critical factor for raw cutting ability, the other considerations are length and handle issues as they influence fatigue heavily. A nice slim and acute edge will of course outcut a thicker and more obtuse one, however even something like the Paratrooper (Martindale), has no problem on grasses when it is blazing sharp, and easily outcuts another thinner model which has seen a few hours of wood working. Handle and balance issues will effect fatigue to a far greater extent than the small difference in cutting ability for the various edge profiles, except in extreme cases. This extends for all the softer vegetation we have around here, which only gets to about one inch or so thick.

As for edge finish, it depends on what you are doing. If the blade is really sharp, you can just chop through the grass like you are push shaving the hairs on your arm. However, if the blade is a little dull this tends to mash the grass down, as its is not stiff enough to support the necessary level of force to excede its rupture pressure, so you have to go to a slice or draw cut, and blade curvature comes into play. The Martindale Golok makes a nice grass cutter because of its sweeping edge arc. The Bolo cuts pretty much with the same effort (edge wise), but induces more rapid fatigue as it is heavier and more blade balanced. Anyway, when you start with this method, as with any slicing, a rougher finish can help, however as you decrease the grit, you need more force to get the edge to move through the material, and it doesn't take much to exceed the stiffness of a blade of grass, as well, if the micro-teeth are bigger than the grass (side on), it won't work well either.

As for wood, similar principles hold. If the material is not stiff enough to overcome the rupture pressure, a chop will just bat it around, and no matter how fine a polish you put on an edge, you probably can't push cut through a briar without it just moving unless you angle along a path to create an internal tension. However since it is much stiffer than grass, and much thicker, you can profit from a much more coarse edge profile and get a deep slicing action. This type of vegetation is usually cut well by a strong edge curvature. Fennell has reported the PM simply excells at it, and can do so with a high edge polish, as essentially the entire edge acts as the little micro-teeth so on a straight edge, sickles being extreme examples of such principles. When the vegetation gets harder, and you can't slice it much at all (even pine resists slicing pretty much 100% with a knife), you have to go back to a high polish, and an angled push cut.


Jimbo :

For moose quarter skinning and such a lot of old timers would only use an old thin bladed knife sharpened with the finest file they could find. It works surprisingly well.

F. Dick made some very fine grooved steels for exactly this type of edge. This is another knife myth - butchers steels destroy edges. Like any sharpening tool, they work well for what they are designed for when used in the proper manner.

matthew rapaport :

Although a thin edge cuts better, and may last longer than a thicker one because it takes less force to make the cut, it also turns the knife into a more specialized tool.

No argument here, exactly as you note, it simply leads to carrying multiple knives. As well you have to take into account what you are willing to put up with. I run my daily work knives very low because if something does happen, I have alternatives on hand, and if it just so happens that I was to run through all of them, I would simply stop such work until I could get that repaired. In some cases obviously, this isn't practical so you have to go with a more overbuilt edge.

Barry :

My Strider S30V AR sure can take alot more punishment at 40 degrees compound than my S30V Sebenza, also at 40 degrees. Two different profiles, two different performance ratios.

Joe Talmadge :

[AR vs Sebenza]

Barry, could this be a result of the Strider's S30V being (I'm guessing) 3-4 Rc points harder than the Sebenza's?

It would make the edge a lot stronger and thus more resistant to rolling and impaction. However if the Sebenza is chipping and not deforming, this implies a lack of ductility and/or impact toughness which should not be induced at the lower RC. Note as well that Hossom and Simonich have now dropped the RC they are on S30V using to 59 according to recent posts. I would be surprised if the Sebanza is at 40 degrees included, the BG-42 ones were a lot more acute. Did Reeves alter the edge profile on the new ones? If anything it should have been made more acute given the hyped properties of S30V.

Barry H :

But the AR has a flat ground blade, and the Sebenza is hollow ground. The Sebenza has a thinner blade, too.

This won't effect the durability of the edge except in a secondary way. For example if the hollow grind of the Sebenza leads to it jamming and thus causing you to twist it, it would fare worse than the AK if you could do the same task with smooth cuts.

-Cliff

 

[Joe Talmadge]

I completely missed Jerry and Rob moving their S30V down to 59 Rc. Did they state why? Was it the same reason that Chris Reeve did it, to make it easier to sharpen? Based on the discussions so far about S30V being about as tough as A-2, I'd think we'd want to really take advantage of the toughness and harden that steel up, as you and many other people have discussed.

Joe

 

[Cliff Stamp]

No, just that it was tested at 60 RC, but they are now using 59 RC. Ref :

http://www.bladeforums.com/forums/showthread.php?s=&threadid=208319

On the hardess, yes, given the hyped toughness of this steel, I expected a hardness at least equal to, and most likely exceeding the norm for what it was replacing.

Of course it will be tougher than the steels it replaces if it is ran softer. With Reeves for example dropping multiple RC points from BG-42 to S30V, even if S30V has the same inherent toughness, or even less, it could still be tougher. A drop of a couple of RC points can induce a ~100% increase in impact toughness.

However the same RC drop will also induce a marked loss in edge retention for many areas due to a lower resistance to rolling (see Goddard, Wilson, numerous post on rec.knives), as well as a loss in impaction resistance (which is what hardness directly measures).

-Cliff

 

[medusaoblongata]

Cliff, thanks for posting this thread.

I've noticed that most (production) knives I buy cut very well NIB, but that edge doesn't usually last very long. The first time I sharpen I cut the bevels down to 17 degrees per side (the thinnest possible on my Lansky) and the thin edge I put on seems to last a lot longer than the thicker factory edge. I guess you just explained why.

 

[OwenM]

Well, Crucible recommends 58-61 for S30V, and Rob Simonich said they were consistently getting 59.5, and very happy with the performance. That's dead center of the recommended range by the steel's manufacturer...
The two S30V knives I've been using are showing some serious edgeholding. The one that has seen the most hard use is ~58-59, and I don't think I'll ever know the difference between it and 420V. Going to try to compare the two (S30V/S90V) when I get the chance. They'll be almost identical edge profiles, identical edge bevels, I'll tape the longer blade off so they're the same length, and they're only about a point apart in hardness. There may be a difference in extended use, I just wonder if it will be significant enough to matter.
They are tough. I convinced myself of that by chopping into a coat hanger with them, INFI, and BM's ATS-34 and M2 a week or so ago, and just today, Camillus' 0170-6C (read that it was similar to A2, which S30V is supposed to be similar to in toughness), and comparing the results. All edges@40* included, except one of the S30V knives, and the Camillus which are at 30. There was no real difference that I could tell between the S30V blades at 30 and 40 included, respectively. The one with the 40* edge may be a point softer (DDR at 58-59 vs. Rinaldi at 59.5 from what I know). The S30V took on a little more damage than the 0170-6C, but the difference is not very noticeable-just a little more indention. INFI@40 was barely affected, and the tiny roll in the edge was gone after a stroke per side on a butcher steel. 0170-6C, M2 and S30V have a small indention in the very edge remaining after being steeled. I think the M2 rolled a little more, but it didn't chip out. ATS-34 took on a ripple in the edge, and a small chip that will have to be sharpened out.
The M2, 0170-6C, and S30V taking on similar damage just tells me I haven't pushed them hard enough to reveal the differences (nor do I intend to-this was just to get an idea about S30V, not tear up all my stuff just to see which lasts the longest).
The only thing that seems out of whack to me, is that apparently there is a "standard" heat treat being used.
I'd think that a lower Rc for greater toughness would make plenty of sense when you consider that alot of these guys like Trace Rinaldi, Jerry Hossom, Rob Simonich, and I'm sure others, are making some good sized knives out of this stuff. I can see where going higher for greater edge retention on smaller knives that don't get used as hard would make sense, but I don't have enough knowledge about this steel (or any others to tell the truth) to know where you start giving up more than you get.
Telling the difference in performance between different heat treats strikes me as being like telling the difference between similar steels in that it would probably take alot of testing and use to really show a significant difference, and S30V simply hasn't been around that long.

 

[Jerry Hossom]

Rc can be very misleading, even if everything else about a knife is held constant. How the specific hardness is achieved will make significant differences in the resulting toughness and edge holding. Rc59.5 using the present HT schedule was basically worked out in discussions with Paul Bos and Crucible metallurgists, with Rob and I providing our thoughts on what we wanted to achieve with the steel in our knives. In our initial testing Rob did his own heat treating and I used Paul, with substantially different schedules than we are now using. The results were excellent, but we discovered the steel had still more to give. Rob now uses Paul for all his S30V blades as does Strider. Rc59.5 using another heat treating schedule might well give substantially lower performance. There are several combinations of hardening temps, quench, cryo and tempers that will get you to that same hardness, but not the same performance.

 

[matthew rapaport]

Rc59.5 using another heat treating schedule might well give substantially lower performance. There are several combinations of hardening temps, quench, cryo and tempers that will get you to that same hardness, but not the same performance.

Is this characteristic of the newer, more exotic steels (BG-42, S30V, etc.) or is it just as true for simpler steels like 1095, or O1? Do heat treat vendors *publish* their schedules or are these closely held secrets?

 

[chad234]

Matthew,
The time/ tempature curves influence all steels during heat treat. Some steels are more forgiving than others.
Think Ed Fowler 52100 v. Marbles 52100 at the same RC. . . . Paul Bos BG42 v. SOG BG42 . . . . Newt Livesay 1095 v. well anyones

You get the point, take care bud,
Chad