Toughness and its effect on grind, performance, and edge

[Surfingringo]

I have been wondering about this for awhile and thought it would be interesting to start a thread about it here and let some of the knowledgable folks on this forum weigh in. I have been wondering how much toughness can affect what kind of grind a knife has and what effects that can have on overall performance.

Here's my theory, which may or may not hold water. I believe that a tougher steel (let's use m4 as an example) that is heat treated to maximize toughness could be ground thinner than a higher carbide steel and still be able to accomplish the same type of work without edge damage. I will use cutting through fish bones as an example since that is something I actually do. I know that geometry always trumps steel but surely steel properties are relevant. I mean, won't certain steels hold up with a low angle edge bevel much better than others? Isn't that essentially the same physics as one being able to hold up in a thinner primary grind? So assuming that one could do certain levels of work with m4 in a thinner grind than say s110v wouldn't that give a tougher steel the performance advantage for more demanding cutting jobs? And if so, wouldn't the thinner grind have a positive effect on edge retention even if the steel didn't have the same level of overall wear resistance?

This has been something I've been curious about for awhile but I don't really have enough steels in enough different grinds to properly test it. Curious to hear from you guys who are more knowledgable about this kind of stuff. I would love to hear Sal and some of the knifemakers that hang out here weigh in on this.

Eta: I'm not really positive that "toughness" is even the right word for what in trying to describe here. All I'm talking about is a steel that is less prone to chipping or deforming at a thinner grind. Hopefully someone will come along and correct my terminology if needed.


Btw, It seems like steel discussion threads here sometimes have a tendency to get weird. How about instead of letting this one get weird we have a good interesting steel discussion? :)

[Ankerson]

There are trade offs to everything.

A lot of will depend on the actual steel, actual edge and blade geometry, actual Hardness, cutting technique and a host of other variables.

What you are talking about has more to do with strength than toughness.

[Cliff Stamp]

I mean, won't certain steels hold up with a low angle edge bevel much better than others?

Yes, however the property isn't strictly toughness which is resistance to fracture under fast loading. To understand why, just make a knife out of a butter knife and use it and watch what happens. A butter knife is very tough (resistant to fracture), you can even beat on it with a hammer, but it doesn't work so well in trying to maintain a high sharpness or resist edge damage (soft, coarse micro-structure).

To start you want to separate a couple of things because they are fairly different even though they may look similar, in short what keeps the apex from resisting damage is related to, but not equal to, what keeps the edge from resisting damage. The reason they are different is mainly because the apex is the same scale in size as the micro-structure of the steel while the edge bevel is much larger and thus doesn't depend as strongly on micro-structure.

For example, take a quick scan though this : http://patentimages.storage.googleapis. ... 274855.pdf" target="_blank and note how in many places they talk about how a higher carbide size degrades the performance as a cutting tool because it promotes rapid breakdown of the apex. However the reason this happens (carbide tear out) won't cause damage to the edge bevel as that is MUCH larger than the size of the carbides. Thus if that steel is better than the one you are using would depend if you are seeing apex failure vs edge failure.

In general, if you want to just maximize strength (and retain toughness) then you look for :

-very fine aus-grain
-high martensite percentage
-high martensite hardness
-low to mid carbide volume, < 5%
-mainly MC type carbides

This produces a steel which has a very high apex stability and very high edge stability (under moderate loads, under heavy impacts like chopping you have to scale back strength to increase fracture toughness and bainite starts to look attractive).

But this steel has a significantly lower abrasion resistance than something with 25% carbide so now you are faced with more abrasive wear vs more strength/toughness? It also has given up a lot of bulk toughness so the edge could chip/fracture under impact far more than a mid-carbon steel.

The problem is that you can't do all of this at the same time. It is like trying to train to win both the 100m sprint and a 50k ultra-marathon, you really need to decide things like :

-do I want a knife to cut very well

or

-do I want a knife which cuts poorly for a long time

or

-do I want a knife which is very resistant to damage, even in extremes

These will take you down different paths in steels, grinds, and abrasives. Just take a look at how your knives fail in use and then you can improve on them by picking steels which address the practical weak points :

-do they rust, well you need corrosion resistance
-do you lose high sharpness too fast, need more edge stability
-is the edge bevel taking visible deformation, need more strength
-is there visible chipping of the edge, need more toughness

In short yes, but it can't be simply regarded as yes/no.

As a side note, there are other complexities when you look at how/why blades cuts which can lead you to pick a steel which takes more damage in use because it is that damage which keeps the blade cutting in some cases.

For example if you look at AEB-L vs D2, then you will see chipping onset in D2 at a much higher edge angle than you will see in AEB-L. The apex on AEB-L will also be much more stable and hold a higher push cutting sharpness. However if you are doing a lot of slicing work then all of that fracture in D2 can allow it to hold a very high slicing sharpness for a long time. Thus if you grind a D2 blade at say 5 dps (with microbevel) you will see damage on set in hemp/cardboard before you will see it in AEB-L. But this damage actually may make you prefer it because it will keep the blade slicing with high force where the AEB-L blade will just tend to wear smooth.

In chopping type blades it is even more of a issue of a trade off because you can increase strength which stops deforming, but if you push too hard into it then you can pass the critical toughness requirement and the edge bevel (or even primary) can blow out. Hence why M4 in competition choppers is underhardened significantly. Yes this makes it weaker, but having a strong blade that has the edge blow out by fracture likely isn't going to win any contests.

[Fancier]

Cliff, are those competition choppers underhardened or overtempered? In case I'm not being clear, I'm making a distinction between a knife that was quenched to a lower hardness and then tempered normally, and a knife that is quenched fully hard and then tempered at a higher temperature. Thanks!

[Ankerson]

Cliff, are those competition choppers underhardened or overtempered? In case I'm not being clear, I'm making a distinction between a knife that was quenched to a lower hardness and then tempered normally, and a knife that is quenched fully hard and then tempered at a higher temperature. Thanks!

Nobody would really know other than a knife maker other than a knife maker who actually makes comp blades and they all have their own formulas for HT and tempering.

Anyone else would be guessing at best and would in turn be complete BS at best.

There are no experts here on that unless one of the makers wants to ring in.

[Surfingringo]

Thank you both. Great info. And Cliff, that was a really informative post. I just finished reading it for the second time! Obviously, the issue is not quite as simple as I would like to make it. (That seems to happen with all sorts of things in my life.) :rolleyes:

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

[Cliff Stamp]

Cliff, are those competition choppers underhardened or overtempered?

It would depend on who does them. Dan Keffler was the first person I noted clearly state this was being done and the early blades which were used with the steel hardened as it is for tooling generated some catastrophic failures and it had to be significantly underhardened to stop the fracture. The unfortunate thing about this was for quite some time people were looking at the competition blades, noting the performance and assuming that they were hardened similar to folding knives and thus concluding it was the super-duper out of all super steels. Dan will be fairly open about how he has it hardened and him and a few others are also now working with 3V changing some of the ways it is normally done to improve knife performance and they have videos on the differences on YT and detailed descriptions of the methods on BF. The background for it (metallurgy wise) you can read in detail in Roman's posts on HypeFree (in short, it minimizes non-martensite phases). I would be cautious in general of assuming that everyone works as Dan does and in general, very general, it is much easier to draw the toughness with higher tempering vs adjust it through under soaking.

[Cliff Stamp]

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

What is the hardest type work you do? Are you splitting, heading, steaking, cutting fins, etc. all with the same knife you are doing fillet work? If you take a normal decent knife and use it then what happens to it - how/where does it fail?

[Ankerson]

Thank you both. Great info. And Cliff, that was a really informative post. I just finished reading it for the second time! Obviously, the issue is not quite as simple as I would like to make it. (That seems to happen with all sorts of things in my life.) :rolleyes:

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

It's best to speak with the knife maker who would be actually making the knife so he can balance the performance based on your needs.

He would be the real expert and much more knowledgeable than anyone here could be.

[Surfingringo]

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

What is the hardest type work you do? Are you splitting, heading, steaking, cutting fins, etc. all with the same knife you are doing fillet work? If you take a normal decent knife and use it then what happens to it - how/where does it fail?

I'm kind of weird as I do the majority of my fillet work with shorter, stiffer knives (even on the larger fish) so yes, it is common for me to do everything with the same knife. The toughest work I do is cutting through 1/8 inch rib bones. Sometimes it takes a fair bit of force. It is not uncommon for me to occasionally push against the knife spine with the heel of my left hand to break through. I am using an M4 blade at the moment ground to about .014 behind the edge. It has performed amazingly and taken virtually zero damage doing this level of work daily. It makes me wonder if something like s90v would have held up to the same level of work in the same grind. It also makes me wonder if I could get away with going just a bit thinner with the same steel (m4). Lots of wondering and not many answers....yet.

[Surfingringo]

Thank you both. Great info. And Cliff, that was a really informative post. I just finished reading it for the second time! Obviously, the issue is not quite as simple as I would like to make it. (That seems to happen with all sorts of things in my life.) :rolleyes:

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

It's best to speak with the knife maker who would be actually making the knife so he can balance the performance based on your needs.

He would be the real expert and much more knowledgeable than anyone here could be.

Yeah, I agree Jim. I'm just trying to gather more knowledge on the general ideas and concepts and figured it might make for an interesting discussion.

[Ankerson]

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

What is the hardest type work you do? Are you splitting, heading, steaking, cutting fins, etc. all with the same knife you are doing fillet work? If you take a normal decent knife and use it then what happens to it - how/where does it fail?

I'm kind of weird as I do the majority of my fillet work with shorter knives (even on the larger fish) so yes, it is common for me to do everything with the same knife. The toughest work I do is cutting through 1/8 inch rib bones. Sometimes it takes a fair bit of force. It is not uncommon for me to occasionally push against the knife spine with the heel of my left hand to break through. I am using an M4 blade at the moment ground to about .014 behind the edge. It has performed amazingly and taken virtually zero damage doing this level of work daily. It makes me wonder if something like s90v would have held up to the same level of work in the same grind. It also makes me wonder if I could get away with going just a bit thinner with the same steel (m4). Lots of wondering and not many answers....yet.

He wouldn't have a clue.... Keeping it real here..

Only actual use would really be the best way to get the answers and it will depend on the variables and the actual knife or knives.

Anything else would be a guess at this point so speaking with the makers would be the best place to start.

[Ankerson]

Thank you both. Great info. And Cliff, that was a really informative post. I just finished reading it for the second time! Obviously, the issue is not quite as simple as I would like to make it. (That seems to happen with all sorts of things in my life.) :rolleyes:

Anyway, I still want to get some kind of thinly ground tool steel optimized for toughness (and strength apparently) and see how it works at the fish cleaning table.

It's best to speak with the knife maker who would be actually making the knife so he can balance the performance based on your needs.

He would be the real expert and much more knowledgeable than anyone here could be.

Yeah, I agree Jim. I'm just trying to gather more knowledge on the general ideas and concepts and figured it might make for an interesting discussion.

Phil hit it pretty much dead on the money with you M4 blade so I would be talking with him on your next one.

Anyone else would be guessing at this point unless they were standing next to you with a variety of knives to test on what you are actually doing.

[Surfingringo]

Yes, phil recently made me an amazing knife. But ultimately, this thread isn't about what my next knife should be. It's about me wanting to get a better understanding of the relationship between different steel characteristics, such as toughness and strength, and how they will respond to (and perform with) different grinds. This is not intended to be a controversial thread in any way. Just trying to learn.

[Cliff Stamp]

[...] I am using an M4 blade at the moment ground to about .014 behind the edge. It has performed amazingly and taken virtually zero damage doing this level of work daily. It makes me wonder if something like s90v would have held up to the same level of work in the same grind.

I would be surprised if you could break the primary grind doing the type of work you are describing unless the fish bones are really hard to cut and you are doing a pretty dynamic almost impact. Everything you are doing technique wise is common locally (mainly cod) as the same knife will be used to steak, split and fillet and even cut out cheeks/tongues. Assuming you have decent skill/control I think you could go under 0.014", but I would be really impressed if you could go under 0.005" doing that type of rough work, easily if you were just filleting . Keep in mind that stiffness is cubic with thickness which means that for example a 0.015" bevel is ~30 times stiffer than a 0.05" bevel.

I would suggest that along with looking at steel you look at geometry because I assume you do most of that heavy cutting with the base of the blade hence you can use a variable grind to really bring out the performance of the knife. Locally the base of the blade will get used for all of the heavy work including heading and the main and tip tend to just see flesh and very minor contacts like rib work. I commonly set choils at 0.025" and taper to 0.005" in tips. I go as high as 0.025" as I have seen people actually use mallets on heavier fish. These knives are fairly basic steels, 12C27 is a very common decent fillet/fish knife steel, 56-58 HRC.

A decent starting point is to take a knife in a decent steel, easy to get a decent fish knife in 12C27 for example, use that with a zero grind and then thicken it until it stops getting damaged. This should set the lower bound for what a decent steel can do. If you can describe some kind of small generic blade you can use I can just send you something in a near zero grind you can play with. I should be able to find a low and and decent benchmark. I would be curious how much higher one would be than the other practically and if the increase in strength isn't simply made non-functional by the loss in toughness. But regardless, knowing how/why each failed would let you know what you need to see the performance improve.

[Ankerson]

Yes, phil recently made me an amazing knife. But ultimately, this thread isn't about what my next knife should be. It's about me wanting to get a better understanding of the relationship between different steel characteristics, such as toughness and strength, and how they will respond to (and perform with) different grinds. This is not intended to be a controversial thread in any way. Just trying to learn.

Pretty much your choices are going to be the same wheelhouse as M4 regarding hardness, strength, edge holding etc.

You might be able to go a little thinner than .014" like around the .010" range depending, but that would take some testing to see.

Strength is going to be the real major factor here as you are pushing the blade through bones especially once you start going thinner geometry.

If you were here I would let you borrow one of my 10V blades that is .012" behind the edge to compare, that would be interesting to see how it would do in comparison, it's in the 63 range. The geometry looks to be about right for what you need.

[Cliff Stamp]

As an aside, materials properties wise, M4 and 10V have no advantage in toughness, and are much lower in apex stability and general toughness than many of the cold work steels which can have equal or better strength. They would have no advantage over them in cutting tools unless :

-failure is mainly though abrasive (or especially adhesive) wear
-hot hardness is needed
-corrosion demands are significant but moderate

The only relevant argument would be for the last one which is why in general Alvin argued that M2 (64/65 HRC) worked better in meat blades than 1095 (66/67 HRC) but not in general utility knives. Not to say it isn't a good choice, it is just far more expensive and doesn't offer increased performance as it is softer, weaker, lower apex stability (weaker and micro-structure isn't the same) and mainly has much higher adhesive wear. The latter is great for tooling, not so much for cutting.

[Ankerson]

As an aside, materials properties wise, M4 and 10V have no advantage in toughness, and are much lower in apex stability and general toughness than many of the cold work steels. They would have no advantage over them in cutting tools unless :

-failure is mainly though abrasive wear
-hot hardness is needed
-corrosion demands are significant but moderate

The only relevant argument would be for the last one which is why in general Alvin argued that M2 (64/65 HRC) worked better in meat blades than 1095 (66/67 HRC) but not in general utility knives.

Not to say it isn't a good choice, it is just far more expensive and doesn't offer increased performance as it is softer, weaker, lower apex stability (weaker and micro-structure isn't the same) and mainly has much higher adhesive wear. The latter is great for tooling, not so much for cutting.

Yeah right.... :rolleyes:

Not from what I have seen over the years.

Clueless as usual.

Beating that same drum is starting to get really old...

How about doing some real testing for once...

Like you used to in the old days, back when you actually had a clue.

[78lilred]

As an aside, materials properties wise, M4 and 10V have no advantage in toughness, and are much lower in apex stability and general toughness than many of the cold work steels. They would have no advantage over them in cutting tools unless :

-failure is mainly though abrasive wear
-hot hardness is needed
-corrosion demands are significant but moderate

The only relevant argument would be for the last one which is why in general Alvin argued that M2 (64/65 HRC) worked better in meat blades than 1095 (66/67 HRC) but not in general utility knives.

Not to say it isn't a good choice, it is just far more expensive and doesn't offer increased performance as it is softer, weaker, lower apex stability (weaker and micro-structure isn't the same) and mainly has much higher adhesive wear. The latter is great for tooling, not so much for cutting.

Yeah right.... :rolleyes:

Not from what I have seen over the years.

Clueless as usual.

Beating that same drum is starting to get really old...

How about doing some real testing for once...

Like you used to in the old days, back when you actually had a clue.

Do you enjoy answering questions directed at Cliff?

[sal]

Sorry, but I have to step in here a bit.

We are all offering opinions. Either our own opinions or the opinions of others. We all would like to believe that our opinions are truth. From God's lips to my ears, but I say it is still all opinion. I have been involved in this game for a long time. I began purchasing testing equipment about 20 years ago because everyone had opinions and they didn't agree. Seemed crazy to me that there wasn't just some facts that I could use to answer my querries, but there just wasn't.

So I invested the money to get to test as much as I could with as much consistenty as possible. I learned how to pound steel, grind steel, heat treat steel and In the final analysis, we can test all we want, but when it comes to edges, one of the more complex entities to study, I find absolutes are questionable regardless of who they come from.

Jim, I know many knifemakers and in many conversations, I find that I know way more about steel, knives and edges then they do. Cliff has his resources and his experiences, Jim, the same. Phil is a great resouce, Ed shempp is another one. I wish I could get Dan Maragni in on our chats. I know and converse with many metalurgists all over the world. But most don't know crap about edges. That's why they send their steel to us to test.

Lance, as I said before, "the edge is a woundrous thing", in all of it's qualities, it is still a ghost. Your questions are valid, but there are many variable to the edge. Everyone here can express their opinion and substantiate it with their own testing, or their experts, or their resouces, but in the end you will have to make your own decisions. Hopefully even do some of your own testing. Get some eye power, loupes and microscopes, keep asking the questions. Find a way to measure edge angles. A goniometer is nice, but expensive.

However, through it all, I will require that everyone be RESPECTFUL to everyone else or I have to shut the whole thing down.

In a effort to find consistent testing methods, I have spent half million in testing equipment and I have a fair amount of experience as well. I don't claim I know truth! I share my opinions and learn from others as to their opinions and come to my own conclusions. I don't always agree, but I always respect. Please do the same.

sal