INFI is the toughest steel?

lsstaipei · Jun 6, 2001

A friend of mine always tells me INFI IS THE
TOUGHEST STEEL.I am not so sure about that because my experience is quite limited.The only steels/knives combination which I work extensively is BK&T Campanion and another no-name,cheap forged 8" fixed blade.My question is,"Is INFI TOHUGHER THAN ANY OTHER WELL HEAT-TREATED STEEL?"For example, tougher than L6,1075? Tougher than CPM 3V? Thanks in advance.

HJK · Jun 6, 2001

Before Cliff jumps in, you have to be very precise. What exactly do you mean by "toughest"?

lsstaipei · Jun 6, 2001

Originally posted by HJK:
Before Cliff jumps in, you have to be very precise. What exactly do you mean by "toughest"?

To me,toughness is the ability of a steel to resist shock or impact.The tougher the steel is,the harder the edge to chip.

HJK · Jun 7, 2001

OK. So it's the edge you're concerned with. That does away with the idea of toughness that makes a differentially tempered blade "tough", as well as san mai type softer cores, which many cultures like the Vikings and the Japanese, considered a vital component of a "tough" sword or big blade.
Those more expert than I [and that includes just about everyone here] might differentiate between a resilient edge which will deform before "chipping" and one which resists deformation at the same level of impact but will break sooner because of its relative inflexibilty. I think you'll find that some prefer a blade that will deform rather than break so the blade in actual use can be "sharpened"[ or straightened] more easily. A chipped knife is a bigger problem. [That's why hamons were used, especially the wavy variations] Bearing in mind that toughness could therefore be two different things, or rather a trade off between two different characteristics of the metal, as forged, tempered, or whatever[ "whatever" like talonite], I expect those who actually have the answers, or more educated opinions, will pipe in shortly.

Cliff Stamp · Jun 7, 2001

HJK:

a resilient edge which will deform before "chipping" and one which resists deformation at the same level of impact but will break sooner because of its relative inflexibilty

That is a very good point. If say for example you left 1095 at around 45 RC the edge would resist fracture very highly, even under really hard impacts (smash it off a rock), you would not chip it out. Compare this to the same edge profile at 60 RC. The harder edge will chip out much easier - however just as you noted, it will resist deformation to a higher degree before it does fail, but when it does it will be a brittle failure, whereas the 45 RC edge will just see plastic deformation.

Now which edge is tougher? Depends on how you are defining tough. In regards to impact toughness, ie. shock, as lsstaipei specifies the 45 RC edge would be tougher. However under chopping on soft to moderate woods the 60 RC edge would hold up better, resisting rolling and deformation longer. The critical point would be if you did really powerful hacking through very hard knots.

Back to INFI, does it have the highest shock resistance of the cutlery steels. No, there are lots of steels with very high impact resistance, S7 for example. While I have not seen any charpy values for INFI/M-INFI, I have never heard Busse claim INFI has this level of shock resistance. What impressies me about INFI is its overall abilities. In any one particular aspect you can readily pick a steel that outperforms it (corrosion resistance - 440A, light use edge retention - CPM-10V, shock resistance - S7), however looking at the overall picture INFI swamps each of those steels in all the other areas. As well, if desired, Busse could differentially tempered INFI, and it would get tougher still - but then it would also get a lot weaker.

-Cliff

Bronco · Jun 7, 2001

Isstaipei,
I reported last year on a situation I experienced with an INFI blade that very well addresses your particular curiosity. While hacking through some dense springy vegetation clearing a trail in the Sierras, I accidently made what was very close to a full power chop into the vertical face of an adjacent granite boulder. The full force of impact was focused directly onto a 2 to 3 mm area of the cutting edge near the choil.

Though the indentation in the edge was readily visible, even under these extreme circumstances the INFI steel tended to deform rather than chip out. The relative strength of INFI was apparent as well, as I was pleasantly surprised that the damage was limited to such a small area. A few passes with a diamond rod hone back at camp realigned most of the displaced steel, and all but erased the damage. No doubt this tiny area is now weaker than the remainder of the edge, but I feel this kind of inherent steel performance is pretty much optimal for an outdoors/survival/hard-use type blade.

I think Cliff pretty much hit the nail on the head when he described INFI as a steel which is unique in its ability to score so highly in so many of the different categories we use to rate steel performance. It is unusual to find a steel that can exhibit such high levels of wear resistance and toughness and strength and corrosion resistance, etc., etc., all at the same time.

You may notice when sharpening an INFI blade that it's somewhat more difficult than normal to remove the final wire edge. The INFI burr seems to have more of a tendency to flop back and forth from side to side when compared to the burrs I have raised with other steels. CPM-3V is a notable exception here; a steel which appears to share some of INFI's other strengths as well.

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Semper Fi

-Bill

Cliff Stamp · Jun 7, 2001

Bronco:

The INFI burr seems to have more of a tendency to flop back and forth from side to side when compared to the burrs I have raised with other steels.

That is usually a sign of an overweakened edge, a too soft hone, or grind marks running parallel to each other. INFI has very hard carbides, to cut them when necessary (which is not often) I sharpen with DMT pads to shape the main bevel and finish with SiC sandpaper on Mylar backing to raise the polish and lightly convex the edge. Cross the scratches on the upper polishes and switch from side to side. This should prevent any burr from forming. Burr formation is also highly dependent on the sharpening angle as well. The lower you go, the less burr you see. My Battle Mistress is currently at about 14 +/- 1 degrees per side with a light convex taper to the edge, about another degree or two at the very last bit (.5 mm or so).

-Cliff

Robert Marotz · Jun 7, 2001

Minor correction HJK...

The Japanese used laminate constructions in swords because it was economical and resourceful to do so.

Don't know about the vikings though, that's not my field.

Shinryû.

Bugs3x · Jun 7, 2001

I'm curious to know if INFI is forged or not. Also, what is its re-sharpenability like? I know it excels at retaining an edge, but most steels which do that, are very difficult to sharpen. Well forged carbon steels can hold a good edge, yet be resharpened quite easily. So curious about whether or not forged, or if not, whether anyone has tried forging it?

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Asi es la vida

Bugs

lsstaipei · Jun 7, 2001

Thank you everyone who replys.Now I know the definition of toughness differs from person to person.
I asked this question mostly out of curiosity.I'm satisfied with my 8" chopping knife.I accidentally chopped into a sand rock with it a couple years ago by a riverside.(I still remembered the feeling
when I realized I chopped it into a rock.)
The edge "rolled".Not chipped.I like it.But this knife doesn't hold the edge well enough(compared with my BM730 ) when whittling wood. One thing I read about INFI in Mr.Stamp's reviews amazes me most is INFI knives not only so tough but also hold the edge quite well when doing low stress cutting.

I don't think I need INFI knives,but now I "want" one.

[This message has been edited by lsstaipei (edited 06-07-2001).]

Cliff Stamp · Jun 8, 2001

Bugs3x:

I'm curious to know if INFI is forged or not.

I would assume so during the manufacturing, Busse Combat does stock removal on their knives. INFI has been forged by (I think) Tim Zowada.

Also, what is its re-sharpenability like?

Problems with sharpening are usually caused by a poor choice of bevel/geometry and/or steel. I have a blade made out of CPM-10V which probably has one of the worst machinabilities of all the cutlery metals. However it resharpens easily.

The metal it well suited to what I use it for (low stress cutting), so it stays crisp with no deformation nor fracture. As well there is just a hint of an edge bevel at a very acute angle, so only a bare minimum of steel has to be removed for a complete sharpening.

As well, proper hones must be used, a high quality diamond abrasive (DMT) will chew through the hardest, most wear resistance steel like its butter. SiC hones will handle all but the upper range of such steels (the very high Vanadium ones), easily.

Anyway, in regards to INFI, my Battle Mistress has a light dual convex edge and I usually maintain it on strop, first canvas and then a couple of passes on the leather side which is loaded with CrO if necessary. This assumes there isn't visible edge deformation that needs to be removed.

The last time I fully sharpened it was a week or so ago as I was starting a comparison and wanted it at optimal performance. I reground the bevel fully on an 8" x-coarse DMT hone, 100 strokes per side, then 50 on a fine, then 30 passes on 1000 grit SiC sandpaper to lightly convex the bevel and finally, 25 on canvas loaded with a white wax/chauk paste.

The blade would push shave with the lighest of effort and cut free standing coarse hair easily (free shave my beard for example). It would push cut photocopy paper as well as slice into freehanging papertowel. The polish could have been improved further with a CrO buff, but I would rather not lose the slicing ability.

I have been working with it this last while. So far it has seen 359 full powered slices into various woods and 508 hard chops in various scrap and felled wood, the latter a mixture of wrist snaps, elbow swings and shoulder drives. Mostly clear wood, only about a couple of dozen knots cut through (they add too much variation to the results I save them for durability comparisions). As well a dozen or so straight cuts through dirty 1/2" poly, and a few test slices.

The edge is still aggressive enough to slice through the 1/2" poly with no slips and only about an inch of travel on a loop-through pull. No edge flattening or deformation is visible. It would be brought back to very near 100% with just some work on a strop. More definate edge retention work later after I finish the cutting.

-Cliff

[This message has been edited by Cliff Stamp (edited 06-08-2001).]

Will York · Jun 8, 2001

Cliff--I really wish you'd be more prudent about publishing the results of your sharpening techniques on the Battle Mistress.

I'm afraid that such graphic representations of frightening sharpness on large blades may lead to legislation banning the application of such edges to anything larger than a straight razor.

Please try to be a little more circumspect.

Thank you--w.

tallwingedgoat · Jun 9, 2001

The toughest steel is probably 4340. It's the stuff they make naval guns and aircraft landing gears out of. There might be some tougher stuff out there, but 4340 would be hard to beat.

L6 is basically high carbon 4340, that's why it is also extremly tough. Howard Clark can do a banite heat treat with it to make it nearly impossible to break under abuse. INFI has only .50% carbon, so it should be tough stuff, though I'm sure it's not the toughest steel ever.

But mostly the knife toughness question is largely academic. Basically I've never came close to breaking an decently heat treated knife of reasonable thickness.

Will York · Jun 9, 2001

Originally posted by tallwingedgoat:
But mostly the knife toughness question is largely academic. Basically I've never came close to breaking an decently heat treated knife of reasonable thickness.

TWG--Blade breakage is a catastrophic failure most will never see, as you say.

However, I'm sure anyone who has chipped out the edge of a blade by cutting hard material, or by torquing against bone or other incidental contact, wishes his blade had been tougher. In these terms, toughness is a very important measurement of edge durability for any blade.

-w

Joe Talmadge · Jun 8, 2001

So Cliff, am I understanding it right that you basically put a standard edge on the knife, and then used the sandpaper after that to make the edge slightly convex on both sides? Or did you just re-convex the one side, the way Busse does it?

Joe

Cliff Stamp · Jun 13, 2001

Tallwingedgoat :

But mostly the knife toughness question is largely academic.

Depends on what the user desires. While it is true that even the most brittle cutlery steels (stainless steels in the ~60 RC range) can easily cut rope, flesh, wood and even bone with only minor blunting, assuming correct technique. There are however a couple of relevant issues. One that applies to any work blade is as Will noted accidental extreme stresses, or fatigue/injury causing improper technique. The other is do you want to be able to do very high impact work if the need arises such as hammer on or with, with the blade? Do you want it to be able to take very heavy lateral impacts? Heavy prying? The latter is however more of a problem with low ductility and resilience than impact toughness but they go hand in hand.

However even simple extended use at a lower level can produce faults in blades. For example the two Ontario machetes that I broke on hardwoods. They lasted a couple of hours of steady chopping on hardwoods and had seen considerable use before that. They could easily handle a few thousand chops, but would break before 10 k.

Of course the latter will weaken any blade. For example one of the first things I did with the Battle Mistress was to see what would happen with the edge if I didn't sharpen it but kept aligning it with a strop. Since wood isn't abrasive, but the impacts are high the edge will deform rather than wear away. After quite a long time (about 100k chops) the edge was that weak that when I chopped up some chicken bones it visibly folded in and I could see light reflecting from it. When fresh, it will handle much larger/harder bones with ease.

So you have to consider both the scope of work as well as the extent of the resulting damage.

Joe, it had the dual edge for awhile, but I converted it to a fully convex edge some time back.

-Cliff

[This message has been edited by Cliff Stamp (edited 06-12-2001).]

tallwingedgoat · Jun 12, 2001

Cliff,

I agree that knives advertised as "survival knives" need to have a certain degree of FUBAR-proof built in. Not necessarily indestructibility, but certainly qualities that inspire trust.

However, in the overwhelming majority of the time, even in the outdoors, knives see relatively low stress work. And in such cases how a knife cuts will overrule other considerations. It is not necessary for knife steel to be "the toughest steel". Reasonable toughness is quite enough.

Problems arise when we don't have the appropriet tools for the job, especially if a light knife is used for heavy work. It would be nice to pay a premium for a super high quality knife that can do everything. But it would be very unsual for someone with a lot of heavy work to do, to go at it with only one tool.

golok · Jun 13, 2001

Dear Cliff,

Thanks for that detailed account on sharpening of steels. It is always a pleasure to be part of the audience when you are giving a tutorial.

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Make Love your strongest weapon. Compassion your shield and forgiveness your armour.

HJK · Jun 20, 2001

Here's a comparison with CPM 10V, if Cliff doesn't mind. The focus is on edge holding. Which is tougher?
http://www.physics.mun.ca/~sstamp/knives/INFI_10V.html

[This message has been edited by HJK (edited 06-20-2001).]

Will York · Jun 20, 2001

Originally posted by HJK:
Here's a comparison with CPM 10V...The focus is on edge holding. Which is tougher?

Without a published index on INFI, it would be hard to define 10V against INFI across the board, as both toughness and edge holding vary in a given steel relative to both RC hardness and heat treat technique, cryo, etc. However, never let it be said that I would allow facts to stand in the way of endless speculation.

As hardness is increased in any given steel, edge holding (resistance to wear) typically increases and impact toughness/ductility decrease. Even though these two steels have significant elemental (and probably structural) differences, I would think that Cliff's 10V hunter @ 62.5 HRC would have a hard time competing toughness-wise with INFI at 59-60 HRC, which is where Busse typically leaves finished blades.

When Cliff was finally able to take the 10V blade to failure, it chipped out, both via the encounter with the staples and to a lesser degree on dirty carpeting, I believe. This is an indication that the blade's strength (and wear resistance) is emphasized over its toughness, both in its construction and in its heat treat/hardness. When Busse edges fail, they typically roll or indent, which indicates the steel is engineered and heat-treated first for toughness and then for edge holding/strength.

The proof of a blade steel is in its performance in edge holding, toughness, strength, and other areas, given the type of task it was designed to perform. The 10V blade outclasses INFI, and most other steels for that matter, as a light-use aggressive cutter with incredible edge life. It also has fairly impressive toughness, given these properties. Similarly, INFI outclasses 10V and most other steels in hard-use blades designed to be tough enough to survive where other blades fail catastrophically. INFI also exhibits impressive wear resistance, given its primary design as a toughness-first, hard-use steel.

-w

[This message has been edited by WILL YORK (edited 06-20-2001).]