RC hardness for taking a beating???

[rustyrazor]

Lets say you were asked by someone to make a survival style knife with the main focus on taking a beating, what Rockwell hardness would you be shooting for? Bare in mind ...I'm NOT looking for differential heat treating or softer spines. lets just say a 6" blade that's primary use was to take a bit of abuse from batonning or light prying and the like. The knife still has to hold a decent edge of course as it's a knife, but ability to withstand abuse being paramount.
...I was thinking RC 57ish but I've been wrong before.

 

[Cody Hofsommer]

Out of what steel? What edge thickness? What grind?

 

[P.Brewster]

If it helps, throwing knives start breaking at around 54 RC (true for simpler steels like 1075, 1084, O1, W1, 1095, 80CrV2).

 

[rustyrazor]

Out of what steel? What edge thickness? What grind?

fair enough... it was more of a general statement, but I guess at this point im looking into 80crV2 and 3V in non stainless for the most part and CPM154 or Elmax generally for stainless.

 

[james terrio]

58Rc seems to offer a very good balance of high toughness and good wear-resistance for quality knife steels. Almost regardless of the carbon or carbide content, that provides a nice sturdy matrix to hold everything together and still keep a good edge. Of course, Rockwell hardness isn't the only factor involved but it's a reasonable baseline to consider.

There are a lot of mass-production knives that attempt to maintain a higher toughness by being tempered back even softer, but all that really "accomplishes" is much faster dulling (wear) and rolling (deformation). They still tend to break the same way harder knives do when pushed too far, or if there are design problems like stress risers, thin tips etc.

Geometry is even more important (or at least more basic) than alloy selection or HT for a knife you really intend to pound on... obviously it will need a thicker edge, less acute edge, and thicker stock overall than hunter/skinner. No matter what steel you use, more of it is more stronger. You might be surprised how much abuse both high- and low-alloy knives at 62 or even 64Rc can take, if they're built right for the task at hand.

 

[rustyrazor]

thanks James. Even though I am not factoring in thicker steel, thicker tips or geometry for this question in particular as I am pretty happy with my designs at this point, but IMHO you are 100%. I have been pretty happy with Peter's and Robs HT thus far and I always have asked for 58/59 for my utility(dare I say tactical... I hate that word) blades as I have never had a problem with one of mine at this hardness yet. I was just wondering how people felt on their ideal hardness for a knife to beat on. That's why I didn't really state steel and whatnot at first. I wanted to keep it pretty general and not get into an argument on using the wrong steel or why INFI is way better than what I am using, lol.

 

[Alpha Knife Supply]

Which is better, a 1 ton diesel truck, a Mustang GT500 or a Honda CR-V? When you generalize you get non specific answers that are not helpful.

Blade steels have optimum hardness levels for hard use. The optimum hardness may be different. For example, for hard use I prefer CPM154 at HRC 59 and Elmax at HRC 61. Elmax is a much tougher steel. If you are going to use Elmax at HRC 59, CPM154 should not be considered. Elmax is that much tougher.

I recommend you choose one of your knife designs and use it as standard for testing. Make the knife using different steels with different hardnesses. Develop a testing routine and test the knives using the routine. Write down your test results. Using this process will give you the information you are requesting.

Chuck

 

[rustyrazor]

Hi Chuck... I'm glad you chimed in. I actually got the Elmax from you in as is, so I'll let you know how it goes I am kind of doing what you are saying, but perhaps from another angle (possibly flawed) and I'm only really using a couple of steels against one another. I know it's general, but I was thinking of a baseline hardness to try em all at I guess... might be backward way of trying it but if I run elmax, CPM-154 and CPMS35VN all at 57/58, then I can see how they perform at that standard and eliminate what I don't like about one or another and play with the one I like the most and call it a day. by all means, if this is missing something let me know.

 

[Nathan the Machinist]

57-58 is pretty soft. Yeah, it probably won't break, but it might not hold up real well either. 57 is gonna be pretty smushy.

Those three are all world class stainless, but I'd try HRC 59-60 with Elmax, it is quite durable. But for a real durable knife 3V has some very nice attributes.

 

[rustyrazor]

57-58 is pretty soft. Yeah, it probably won't break, but it might not hold up real well either. 57 is gonna be pretty smushy.

Those three are all world class stainless, but I'd try HRC 59-60 with Elmax, it is quite durable. But for a real durable knife 3V has some very nice attributes.

Hey Nathan. Do you mean "hold up" as in edge holding? that is secondary for these ones as they have to come back.. even if they come back duller than they potentially could have I would rather that over a catastrophic failure like a broken blade. Agreed 3V is one I have along with 80Crv2 for hard use, but I do need a stainless option as well.

Thanks again for the imput to all of you guys. I really respect the opinion of everyone who has taken the time to give their two cents... I mean always have, not because you answered

 

[james terrio]

... if I run elmax, CPM-154 and CPMS35VN all at 57/58...

In my experience, Elmax will smoke CPM-154 and CPM-S35VN at 58 or at 60Rc. Both in brute toughness and general edge-holding. (and 154/S35 are both dang good steels )

I currently have Peters run both 3V and Elmax (as well as 154/S35) at 60 for rough-work knives... and everything else. I may still be leaving some performance on the table; just haven't gotten round to finding out yet.

There's a certain point where you can "performance" yourself right out of the market. Like it or not, perception is reality to a whole lot of buyers, and many of them still fear breaking or not being able to sharpen harder, more "exotic" blades. Much like the old "stainless vs. carbon" thing, that's not nearly as big of a deal as it was 40 or even 10 years ago, but it does still happen. Just something to consider.

 

[rustyrazor]

yeah. I totally see that... Perception is one of the biggest arse pains in the knife world IMHO. you get so many being soooo critical of something because it's not next year's steel or "it's not as good as______" meanwhile most will never use any properly heat treated blade to anywhere near it's potential. I am in the military and most of my clients are army guys who really misuse knives to the fullest and I've never had anything but compliments and how "amazing this steel is" meanwhile, more than one of those knives were from the old days when I was using plain ole 440c... no kidding! if they listened to most steel snobs they would quickly be convinced that they had the most useless steel imaginable and their knife wasn't good enough, but since they got these with no prejudice and just used them they are totally happy... and return customers in most cases. bare in mind I have moved on from 440c for hard use knives as there are just tougher steels out there but I can't imagine how tough a knife has to be if it has to be tougher than what I need... and I've done stuff that would sicken most knife lovers. funny thing is that my own blade I have carried on 3 deployments and countless other exercises is made of 440c as well... you know, from back when I didn't know any better but what can I say? It's got some sentimental value to it at this point.

 

[the possum]

I'd suggest taking a look at toughness comparison charts from various manufacturers. Compare what you see to steels you are already familiar with, and see how much toughness you need, versus hardness or other things, like stain resistance.

M4 - 15J @ 64
440C - 22J @ 58
CPM S90V - 26J @ 58
D2 - 30J @ 59
CPM M4 - 38J @ 63.5
S30V - 38J @ 58-60?
M390 - 41J/sq cm @ 58? and 32J/sq cm @ 63 (unknown test method)

O1 - 41J @ 62 (61 to 63)
3V - 53J @ 62 and 113 @ 58
A2 - 56J @ 60 and 42J @ 61
L6 - 58J @ 61 and 93J @ 57
S7 - 169J @ 57
S5 - 198J @ 58-59
4340 - 55J @ 57 (Charpy V notch test)


For the ultimate in toughness, I'd like to know if something can beat S5 at around 59 Rc.

 

[rustyrazor]

Hi Possum... thanks for your reply. I'm not really interested in charts as they relate to usable knife hardness. Yes, you can compare lines against lines in a graph and that gives you an idea of how they compare using the given testing parameters for each. Bare in mind each may be tested different and who knows where they got their info... C notch Charpy vs U notch will yield massively varied results and may throw your perception off and Hardness doesn't always translate to usable cutting edge... Not to mention the ability for a normal hunter, soldier or bushcrafter to be able to resharpen that diamond hard blade in the field. "ability to take abuse" in knife steels is more than just the "toughness" by the numbers used by engineers and metalurgists.. which is "the ability to resist brittle fracture" but by this definition as long as a blade doesn't break it's tougher than one that does, but in real use what is worse, a knife that has a small chip out of the edge when hitting something harder or one that has huge plastic deformation? That is the balance, and that is what I was asking in this post in particular. What you guys believed to be the best RC for "ability to take abuse"... Chuck, James and Nathan all have no concerns with em between 59- 60 for the steel I'm interested in whereas I had it in mind a bit lower.. and now the testing begins.

Note: apologies if anyone had misunderstood "toughness" for ability to take a beating.

 

[jdm61]

One thing that those charts don't tell you is what kind of edge each steel will take. Most people consider 3V and L6 to be VERY suitable for knives. According to Crucible, the impact resistance of 3V at 60Rc is in the 95J range, but it takes a NASTY fine, stable edge at that hardness and holds it for a while. S5 and H13? Not so much. From what Scott Gossman tells us, S7 is super tough and can be heat treated to take a good edge but with the emphasis still being on the tough as nails aspect. From what I understand, Elmax will give you a fair bit more toughness than the M390 with a corresponding reduction in wear resistance, but at the 60Rc or higher change, that reduction seems to be like 20% or less.

 

[the possum]

I was suggesting to use published data as a guide. You still have to decide where to find the balance of properties for your application, which is really getting at the heart of the art, as you mentioned. L6 won't be the best choice if your primary mode of edge dulling is by turning into a rusty mess in the sheath. If your primary purpose is cutting rope and carpet, you need a lot of wear resistance. If the edge is rolling too badly, you need more hardness for strength. If the edge is chipping, you need more toughness. Etc.

but in real use what is worse, a knife that has a small chip out of the edge when hitting something harder or one that has huge plastic deformation?

The Rockwell hardness test is basically a direct measure of plastic deformation. If you're comparing two different steels at the same hardness (say, 59 Rc), then neither one should have noticeably more rolling or denting than the other in "real world use". But with different steel chemistries, it's entirely possible that one of those blades would get severe chipping from impacts, while the other is essentially unscathed. I can agree with you in principle, that we're shooting for the best overall edge durability, and small nicks are preferable to huge dents.

 

[james terrio]

Charts like that mostly tell us that someone somewhere knows how to cobble a bar-graph together. They're not generally uniform in what they measure, therefore not terribly accurate, and as such they can be very misleading.

Overall Edge Stability, as folks like Nathan have attempted to define and test, is a bit more complex than "mere" Rc values or carbide content might suggest. Lath vs plate martensite, retained austenite, and many other factors play a big role even when comparing various blades made of the same alloy.

 

[rustyrazor]

and that's why I'm not a metallurgist... I just make em and beat on em and see what I like. Thank god you guys came along or I would have taken forever to get to where I am now, and that's still pretty pathetic, lol.

 

[Augus7us]

Rusty didn't you just buy a kiln? All this rockwell talk is just going to make you want a tester next. Get out while you still have money

 

[Lo/Rez]

When stone washed 3V can be fairly corrosion resistant. It certainly can take a beating.

[video=youtube;IcovoTyGiRg]https://www.youtube.com/watch?v=IcovoTyGiRg[/video]