Toughness

[Noddy]

I wonder if this is the place to raise the issue of toughness in a knife.

I was reading around trying to find out if 3V was a rust maker. Too much contradictory info, in the end

The question I had in mind was, overall, in terms of geometry, hardness, and steel type, what would you go for if you wanted a knife that you could hammer the hell out of.

Let's just say, for the purposes, that resharpening is something that you would expect to do in a day's use of such a knife, but that you probably wouldn't want to do three or four times in a day.

A note: I had this chisel once, a 3/4". Never knew who made it - and it wasn't a Stanley or anything recognisable - it wasn't a cheap one, I don't think, and it just turned up in the shop one day. But, I could use it all day on hardwoods and knotty softwoods, and the edge would only just start to lose its real bite a little bit at the end of the day.

I wish I knew what that one was made of. :)

So what is it? L6, O1, VG10, A2, D2 ... kind of hoping for an answer in the stain resistant range of things. Convex, scandi, flat? How thick? How broad? Sharpening angle. Bellied or not? Differential HT, soft, hard? All that.

The point is that a number of things contribute to the toughness of a blade, not just the steel recipe. Is one of these factors more important than others though?

[mr doyle]

I got an Alan Wood Picos model in A2. I don't have a picture but its a small knife with a hollow grind. At first I was a little snobbish of the steel and never really knew anything about it. After a fair bit of use it seemed to hold an edge incredibly well. The more I used it the better it seemed to be and I began to use the knife a lot harder and for the more dirty jobs around camp.Keeping in mind that this is a knife with quite a slim profile I was, and still am, incredibly impressed with its toughness and edge holding of this particular steel. It does stain a bit like 01 but but is easily cleaned.
The pioneer model Alan did were mostly A2 and I wish I snapped one up. Apparently the steel is quite expensive which is perhaps why you don't see al of of it around..
My personal opinion is that it knocks the socks of 01 in terms of toughness and edge holding, but that's just me.

[Noddy]

So, I am sitting here doodling and thinking - and what is worrying is the speed with which these meditations circle round and end up producing something like a woodlore - probably leafing through the Show Us Your Bushcrafter thread is the root of it :lol:

At the moment, for toughness, I am thinking a slightly convexed, highish scandi in slightly soft A2, D2 or 3V. A spearpoint about 4" long, with a long handle.

I wish I had more imagination. It is tragic, really it is.

[Iron Hoarder]

Use D2. It's used for forming tooling in high speed stamping dies.

[Eee]

I've heard a few people on here be really rude about D2 when it comes to toughness. I don't own any, so can't really comment. M4 seems pretty tough at high hardness, even with a thin edge.

I'm interested to hear more knowledgable opinions than mine though. A2 and 3v are both steels I would like to find out more about.

[GHEzell]

If you want toughness with a good degree of edge-holding, it is very tough to beat L6 with a 58-59 rockwell c hardness.
It will rust if you look at it funny, though.

[Noddy]

So, just to get things straight so I know - lower Rc means improved toughness - or does it just mean that it will roll/deform rather than snap?

I think what I mean is does Rc affect toughness in any way other than making the metal malleable?

Does 3V, say, get as fragile as anything else at high Rc?

...

I suppose my question is this: I get an axe shaving sharp easily, but it doesn't stay that way. If I wanted axe like qualities in a knife how would I go about getting them, whilst not having to resharpen all the time?

[Folderfan]

Noddy mate, if you ever get this all straight, will you explain it to me please?

I'm getting a headache just thinking about it all.

Alex.

[Everything Mac]

I've never really used a broad enough array of steels to give a decent answer but I made a scandi a while back...the thing was awful as I couldn't get the grinds right and I very nearly binned it.

I forged it from an old ball bearing casing - ended up putting a micro bevel on it.

The edge retention is simply outstanding. Very very impressed with it.

Andy

[Eee]

So, just to get things straight so I know - lower Rc means improved toughness - or does it just mean that it will roll/deform rather than snap?

I think what I mean is does Rc affect toughness in any way other than making the metal malleable?

Does 3V, say, get as fragile as anything else at high Rc?

...

I suppose my question is this: I get an axe shaving sharp easily, but it doesn't stay that way. If I wanted axe like qualities in a knife how would I go about getting them, whilst not having to resharpen all the time?

My understanding is pretty much based on the internet, so I'm no authority, but goes something like this...

Toughness, wear resistance and hardness are all desirable. Different steels have different ranges of effective hardness. Knives seem to generally be between Rockwell C 55 & 65. Edges seem more and more likely to roll or deform at lower hardness. Many 'hard use' knives seem to be around the 57-58 point but some steels seem able to get good toughness at higher hardness. A 'good' heat treatment is reputed to be helpful in maximising the qualities inherent in the steel. Have a read of this article and see if it helps.
http://www.simplytoolsteel.com/choosing-the-correct-tool-steel.html
Look at CPM 9v - it looks great until you realise it's difficult to get to a decent hardness for a knife. So CPM M4, 3v and A2 all look good for toughness at knifey hardnesses

[mrcharly]

I have an adze that I love/hate. The steel is difficult to sharpen - most files skitter off it. A chainsaw file will cut it, but is the wrong size (I made a mess of the bevel using a chainsaw file). Stones just seem to gunge up when used on the steel.

I don't think it's particularly hard steel (going by what happens when sharpening with waterstones), but it is certainly tough. It's a Mueller adze, btw.

[fluffy]

This was pretty tough.
Farid was making some dive knives and brought one around to generally try to destroy in the garden.
http://i227.photobucket.com/albums/dd71/SharpFluffy/Russell%20White%20Feb%2010/IMG_0435.jpg
It did well on bricks and batons, as well as wood and endured 4 blokes trying to bend it by bouncing on the blade.
(now a garden knife for my wife:- gets much more abuse)
Rockwell in the 40's IIRC.

Or he goes for the CPM REX121 for mad tough steel

[ScotchDave]

So, just to get things straight so I know - lower Rc means improved toughness - or does it just mean that it will roll/deform rather than snap?

I think what I mean is does Rc affect toughness in any way other than making the metal malleable?



This is a surprisingly complex question, toughness vs Rc mostly does follow the relationship you describe, for example 40Rc will be tougher than 55RC.

However, there is some non linearity in this curve, so depending on the steel one can have a 57Rc hardened blade that is tougher than 55Rc in some steels.

This whole matter is complicated by the fact that toughness is a materials property that is affected by the geometry of the sample. The same steel with the same heat treat will have a different fracture toughness for different shapes. There are dimensions at which fracture toughness becomes constant for different geometries, but normally knives are not within these parameters.

I hope that you find this answer useful/interesting,

Dave

[Noddy]

Scothch Dave, I do find that interesting and you sound like a man who knows a thing about steel

I have read some on the internet about steel, but it is all a bit layman's and approximate - which is fine, because that is what I am, especially the approximate part

But if I wanted to read like proper books on steel metallurgy that might lead to a better grip on toughness, any notion where I could start?

[etorix]

i recently took another approach to steels-research, lookin at its surface for etching qualities, check the links in this thread http://www.britishblades.com/forums/showthread.php?130379-A-Guide-to-Etching-Specialty-Alloys

if you look at Carpenter's site fr'instance [Facebook page even] theres a bunch of white papers about tool-steels

not all of which applies to KNIFE usage, and, as usual, heat-treatment is vital

Bob Dozier seemed to make the best use of D2, and historically seems to be its first user for knifes

his 'successor' Tom Krein gets his D2 Heat-treated at Peters Heat Treating. http://petersheattreat.com/cutlery.html [i have an example on the way]

what I'd really like to see also is the research papers behind Takefu http://www.e-tokko.com/eng_index.htm .. they developed VG-10 [amongst other nice flavors]

[Noddy]

Thanks Aed

and thanks for the pic Fluffy - what was the steel?

Not sure what battening a brick tells me. Some London bricks have small flints in the aggregate - other bricks are of wonderfully refined clays, but you can start to carve in them with your finger nail :)

It's not quite a cold chisel I am after - (fink axe - though if you do, the answer might come out quite simply Fallkniven)

In the end, part of this question is about what you an reasonably ask a piece of knife shaped metal to do. But it isn't possible to answer that without knowing what a bit of appropriately ground and HT'd 3V is reasonably capable of

Geometry must be important here. The thick steels and near obtuse convexed edged of Fallkniven allow for a situation where the actual edge of the knife doesn't lead in all the cutting/splitting. After the first blow, the cheeks of the blade supply all the leverage to open the wood out. The edge doesn't necessarily remain in contact.

[ScotchDave]

Scothch Dave, I do find that interesting and you sound like a man who knows a thing about steel

I have read some on the internet about steel, but it is all a bit layman's and approximate - which is fine, because that is what I am, especially the approximate part

But if I wanted to read like proper books on steel metallurgy that might lead to a better grip on toughness, any notion where I could start?

Hi Noddy,

I don't know as much about steel as I would like, most of my knowledge comes from coursed I've taken as part of my education, many of them without textbooks.

For basics I like Callister's materials science book, but it covers a huge area of materials, mostly stuff that isn't relevant to steels. I also like meyers mechanical behaviour of materials, which again covers a large area. I have a friend I can ask for a recommendation as he has a rather extensive library of metallurgy books and is a mastersmith.

Dave

Dave

[Noddy]

I would be very grateful if you could ask, Dave. Thanks :)


EDIT: Austenite, the relationship between heat and ductility, Charpy testing, eutectoid points …. Erm, this stuff is actually interesting.

Going to strt with AA Grifiths I think. Can't dislike a guy who got fixated on how cracks behave :)

[mrcharly]

I've had an occasion to ponder this with a couple of knives.

I needed to cut up a large coffee tin (a '1 gallon' tin) and my tin snips were 10 miles away. So I picked up a knife - the first one was an Opinel - it was hopeless. The edge folded over immediately.

The other knife to hand was my marine SAK. I managed to slice up the rest of the tin, severely blunting the knife in the process.

Now, the SAK has a very soft blade. It isn't much thicker than the Opinel, but had a more acute bevel. I assumed the Opinel, convex sharpened and with quite hard steel, would survive better than the SAK. I was wrong.

I tackled my adze again, in front of the tv. Coarse emery cloth wrapped round a pipe. About an hour's rubbing away didn't seem to remove much steel and even with stropping the edge ain't no hair shaver. But it does cut wood now, I get that lovely shnrick sound.

[FGYT]

any body play with a Banite Martinsite HT mix ???

this would be a soak long enough to form some Banite but then quenched to form martinsite as well so needs tempering

http://www.heatreat.de/en/news/detail/149/Column/Shortened-bainitic-treatments-of-steel-showing-increased-properties/


ATB

Duncan

[ScotchDave]

Never played with it, but according to my highly calibrated "that's about" meter those HV numbers should be in the low 60s HRC. Because HRC is linearly related to strength, I predict that it will be strong, but I have no idea about how tough. Without a good toughness value it could be a very chippy steel.

It would probably be worth playing with, but I have no idea if the toughness will be high enough.

Dave

[shing]

Steel makers have produced steels for different purposes.

Of course, users would want a knife that is as hard as possible, as tough as possible and resist corrosion. As this is not possible, makers and users have to compromise when choosing the steel for a knife.

D2 is good at resisting abrasive wear which is why its used for planer blades and stamping dies. Its is not a very tough steel relative to other steels so its not used where it will be subjected to shock loads such as hammers and chisels. A knife made of D2 would be good used to cut abrasive materials like wood with silica inclusions and animal skins covered in sand and soil.

3V is a very tough steel and can be used for hammers and chisels but its not as good as D2 in resisting abrasion. A knife made of 3V would be good for batoning and prying but would get blunt quicker if used to cut abrasive materials.

D2 and 3V also demonstrated 2 modes of knives getting blunt. D2 would resist abrasion but be more prone to micro chipping at the edge while 3V would resist micro chipping but be abraded faster than D2. Edge geometry is thus important.

Knowing this, the knife maker can design the knife to maximise the strengths of the steel he/she is using while minimising its weaknesses. The maker can also vary the heat treating process to bring about the best combination of hardness and toughness depending on the intended use of the knife. So while D2 is not a very tough steel, it can be heat treated to make it tougher or treated to make it harder with a lose of toughness.

[Noddy]

Thanks for that Shing. Have you had any experience working with A2?

Also, FGYT, I get the impression that Bainite is a good thing re. toughness. Is it tricky to produce?

I have heard of it, in a BB controversy a few years ago.

[ScotchDave]

Thanks for that Shing. Have you had any experience working with A2?

Also, FGYT, I get the impression that Bainite is a good thing re. toughness. Is it tricky to produce?

I have heard of it, in a BB controversy a few years ago.

Interesting, if bainite is tough then the steel FGYT described is definitely worth a bit of play time.

There are unfortunately holes in my knowledge of steel that come from being a materials scientist rather than a metallurgist. Hence the foot in mouth. :)

Dave

[shing]

Thanks for that Shing. Have you had any experience working with A2?

Also, FGYT, I get the impression that Bainite is a good thing re. toughness. Is it tricky to produce?

I have heard of it, in a BB controversy a few years ago.

Yes

[Noddy]

I wondered what your opinion of it might be as a cutlery steel, especially with regard to its capacity to take impacts without chipping and its capacity to take and hold a sharp edge

[TLM]

Good reading if one has the basics: http://www.msm.cam.ac.uk/phase-trans/newbainite.html. It does explain a lot about bainite but does not answer directly the important question: "which steel for bainitic knife".

[FGYT]

Thanks for that Shing. Have you had any experience working with A2?

Also, FGYT, I get the impression that Bainite is a good thing re. toughness. Is it tricky to produce?

I have heard of it, in a BB controversy a few years ago.

its something im looking into

Some things i read it looks good others looks not so much

i think i will try some and see


not difficult to do if you have the right gear which the Heat treaters i use have ;)

ATB
Duncan

[Noddy]

I found the university library here has a metallurgy/material holding - I think I might get them to order that Bainite book

There's this quite recent BB thread too - didn't show up when I did a search forst time, but here it is now:)

http://www.britishblades.com/forums/showthread.php?131792-Toughest-knife-steels&highlight=bainite

[shing]

I wondered what your opinion of it might be as a cutlery steel, especially with regard to its capacity to take impacts without chipping and its capacity to take and hold a sharp edge

I can't say as I only made one A2 knife and never used it. I don't have the facilities to test blades on a scientific basis. I don't think chopping wood with different knives is a good way of testing them as it is not reproducible.

Different steels do not differ that much. While a steel that is 10% better at edge holding is significant from an industrial users point of view, users of knives that are 10% better at edge holding than another knife would be hard pushed to tell them apart. Most steel producers do not have the knife maker or user in mind, their main markets and hence their products are aimed at the industrial users where even a few % increase in edge holding or toughness is worthwhile but its not the big differences in performance knife users might expect.

[Noddy]

Thanks for that perspective Shing.

That said, I have a 440A knife and soft 12C27 one that I don't think I could make chip if shot at them with bits of Thames ballast :)

On the other hand it is true that they have the edge retention of a milk bottle lid.

One of the reasons I am asking all this, is that I have a Roselli axe which is noticeably harder than my other axes. It cuts like crazy, and stays sharp for a long time. It also has a edge preserving geometry - a very thick, full convex. It did chip, but only after a glancing blow sent it into the edge of a concrete path. I am letting the chippage work itself out through resharpening, rather than fixing it in one go. But what I mean here is that the axe has the kinds of qualities that I found in the chisel I mentioned at the top of the thread, and that I would like to reproduce in a knife at some point.

[ScotchDave]

The book TLM posted has an interesting section of temper embrittlement: http://www.msm.cam.ac.uk/phase-trans/2004/z/3750-012.pdf

Dave

[Chris Grant]

EN45, for a big chopping knife with a convex edge is wonderful, very impressive.
I like two German steels as a midway compromise between simple steels and tool steels, they are 75CR1 & 80CRV2, I am really happy with their edge holding and their toughness is outstanding.

TLIM & Kevin Cashen will attest to how 52100/NC6 will perform as bainite. O1 is a mean beast made bainite too. One day I hope to give it a go.

My Pal Douglass2009 works in Vanadis 4E and if you're looking at CPM-3V...look at Vanadis 4 too!

PS are you intending to make an ideal 'toughest knife' yourself Noddy?

[Noddy]

... are you intending to make an ideal 'toughest knife' yourself Noddy?

Me? No. but I would like to get myself in to a position where I could form an educated opinion as to what I'd want in terms of geometries, steel, heat treatment and so forth. Then I might be able to approach someone with a clear idea and explore the possibilities of it being made.

Thanks for opinion on EN45 and the gruntiness of bainite structures :)

[Chris Grant]

What size of knife are you thinking about?

Me? No. but I would like to get myself in to a position where I could form an educated opinion as to what I'd want in terms of geometries, steel, heat treatment and so forth. Then I might be able to approach someone with a clear idea and explore the possibilities of it being made.

Thanks for opinion on EN45 and the gruntiness of bainite structures :)

[Noddy]

Something 4" and a bit, and something up to 8"

However, the 8" might go on permanent hold. I just ordered up a knighton billhook - which may well be the thing I am looking for - and then there is a 8"x5mm convexed leuku idea that I want to try out too - I had the notion in abstract for a while, then saw something bwildered had made and that had me completely convinced. Might do that one in the fancy steel/HT :)

Even just describing it makes it more and more tempting

[Chris Grant]

Interesting...Working right now on a 8" full convex leuku for RCS at the moment in 6mm thick clay hardened 75CR1, will give you a shout when it's done...

Fancy steel's good, but simpler steels seem to be tougher...
For a leuku that size, I'd recommend 75Cr1 or 80CrV2, both are now sourced in the UK.

What you'll choose for the 4" knife will be interesting... If it were me, 3V, Vanadis 4 would be contenders.

PS I really like 12C27 a lot, if the heat treatment's done right, it's ace.



Something 4" and a bit, and something up to 8"

However, the 8" might go on permanent hold. I just ordered up a knighton billhook - which may well be the thing I am looking for - and then there is a 8"x5mm convexed leuku idea that I want to try out too - I had the notion in abstract for a while, then saw something bwildered had made and that had me completely convinced. Might do that one in the fancy steel/HT :)

Even just describing it makes it more and more tempting

[Noddy]

Working right now on a 8" full convex leuku for RCS

There is something about the likeness of great minds :lol:

Thanks for the leads on those steel choices

I look forward to seeing how that leuku turns out

EDIT: http://www.britishblades.com/forums/showthread.php?t=30892&highlight=bainite+rose
EDIT: http://www.msm.cam.ac.uk/phase-trans/2004/Bain.Alloying/ecbain.html
EDIT: http://www.msm.cam.ac.uk/phase-trans/bainite.html

[Noddy]

Ok, so I had a little chat with Fluff about relative merits of 3V and L6

An L6 convex bushie/heavy kephart - I now wonder. I have to say that I am all over the place with this dilemma I have set myself.

Anyway - what I need to ask is this: Is L6 really going to crumble to rusty flakes if it discovers there is such a thing as salt and vinegar crisps? You get my drift.

It can't be that bad, can it?

Or, can it? :)

[Noddy]

To make things more complex yet:

What is the CPM 9V that Eee mentioned earlier?

http://www.knifeforums.com/uploads/1264969733-Steel_chart_2_.jpg


EDIT: Ah! Re. 9V: "If hardness >HRC 56 is required, consider using CPM 3V or CPM 10V."

Interesting graph that, if it is right - D2, M2, 440C, 154CPM, all more or less the same regarding toughness and wear resistance

Pity 9V wont get just a couple of Rcs harder - maybe there is more to know

EDIT:EDIT: Just be rereading notes on 13C27 - sounds a bugger of a steel to work, but great once made up

[Noddy]

weird doubler

[Chris Grant]

I have some 3mm 15N20 which is quite similar to L6. I've made 4 knives from it and staining did not seem to be a big problem. Maybe the nickel....

*cough* Vanadis 4E...

[Noddy]

Tunes, man :)

You mean

Vanadis 4E

Description:- Vanadis 4 Extra SuperClean3 is a high alloyed powder metallurgical tool steel suitable for long run tooling in applications with high demands on adhesive wear and chipping resistance.

Vanadis 4 Extra SuperClean3 is the best tool steel for long runs in applications with severe chipping problems.

Size Range:- Available on request.

[Thinker]

Ive been reading through all this and find it all very interesting, will watch closely to see how this develops.
Ive got a question though, say you introduce a forged blade into the equation too. I know there has been some debate on here about the refining of the edge grain through the forging process, so would a forged blade perhaps have additional qualities adding to its strenth or toughness or is it much the same?

Just a thought ;)

[neo]

Some other graph

http://corse76.altervista.org/col.php?noti2=resilienza

[Noddy]

Thanks neo - taken together these all help.

[fluffy]

Farid is doing a run of CPM Rex121 bladed K2s.
You might want to plump for one of those or accept that a Serrata will be a great cutter if you wipe it on almost anything.
If you want tough, take a hammer.

[Noddy]

I would but the K2, as grand a thing as it is, isn't my cuppasoop unfortunately.

Rc 70 ... FFS! :ralmao:

There's cooking going on in the background here :) In any case option exploring is always fun, "as well you know" (quoting E. Izzard) :lol:

Interestingly enough, my dad always told me to watch playing with hammers in case fragments flew off :)

[Noddy]

Just got asked to take a quick look at at a BRKT Canadian special in 3v.

A friend picked one up a while ago in bamboo (which turns out to be hard, chippy stuff). He'd taken it round the dojo and someone had done some whittling on a another bit of bamboo. I haven't got the full story on what was going on but the edge at the tip section of the blade (about 2cm) had chipped up pretty badly, almost crumbled.

Don't know if it is a BRKT, thing, a HT thing, a 3V thing, or a silly bugger thing.

Is bamboo notorious for mucking edges up?

[douglass2009]

Cheers Chris, but working with steels for living ( im a toolmaker /engineer) ive found all steels have different propeties dependant on how they are heat treated, in 28 years of toolsteel usage the best steel ive found for edge retention and toughness is caldie by uddeholm and its an air hardener, vanadis 4 is great for producing a sharp edge that will last on abrasive and difficult woods/hide but requires cryo heat treat to get the best from it, A2 and D2 perform well just its difficult to resharpen once the edge is gone, but not impossible, ive tried 52100 and im quite taken with that too (cheers Chris) so it is all subjective as to what you want to use really.

EN45, for a big chopping knife with a convex edge is wonderful, very impressive.
I like two German steels as a midway compromise between simple steels and tool steels, they are 75CR1 & 80CRV2, I am really happy with their edge holding and their toughness is outstanding.

TLIM & Kevin Cashen will attest to how 52100/NC6 will perform as bainite. O1 is a mean beast made bainite too. One day I hope to give it a go.

My Pal Douglass2009 works in Vanadis 4E and if you're looking at CPM-3V...look at Vanadis 4 too!

PS are you intending to make an ideal 'toughest knife' yourself Noddy?