is this a good demo of hardness and toughness?

I don't know what was said during any of that.

I'm not sure what that 'test' proves and how it relates to knives. In my lowly opinion, it's a terrible test of anything knife related. Do you plan on sticking your knife in a vise and hitting it with a hammer? I'm not trying to be a jerk. We know nothing of what happened there...unless you speak the language.

Ultra high hardness seems to be, at least to some minor degree, at odds with toughness. And edge geometry plays a HUGE role in all things knife related.

For those of us without high tech analysis equipment or even Rc testers, the best thing we can do is pick a suitable knife steel that we can get the best heat treat out of with our equipment, decide what it is that we want that blade to achieve, choose a tempering temperature within the proper range to best suit the intended use, and tailor the edge geometry to suit the intended use. Then, spend an hour or two around the shop cutting things that the knife was designed to do and see how it lives up to your expectations. That's the best test you can do.

People forget that knives cut and slice things. That's it. They really make lousy choppers, prybars and screwdrivers in the grand scheme of things. And if they do happen to chop, pry or hammer things well, they probably are really lousy at slicing things.

Putting a coupon of steel (of unknown alloy and heat treat regimen) in an Rc tester (do we know if it's accurate even?) for one reading and then putting it in a vise and banging on it with a hammer is pretty worthless to me. It tells us nothing of how well a knife blade will perform.

Bluntly speaking. :) No offense to you at all, Scott.
 
the coupon was 1.2519, heat treated like most oil hardening steels, 825C for 10 minutes, quench in medium oil, probably tempered at 400F. was just surprised to see how the coupon behaved, that's all. i had a blade of O1 tempered to Rc62 that snapped like a twig when i tried to bend to tang by hand. and remember, we have nothing to fear except fear itself and the boogie man.
 
If you didn't notice, there was some give in that vise mounting. Still interesting, but I would agree with J Doyle overall.
 
If I claimed I could write the longest post in the history of this forum, and then proceeded to type a doozy, in which I used gibberish and unrelated snippets cut and pasted together simply to reach the required proportions, I would prove my claim… But what would any of it mean and what value would the information have? Not that I am picking on this one example since the vast majority of all “tests” that I see tossed around in knifemaking fall under the same category- impressive displays that really mean very little and provide no applicable data.

We are talking about toughness here, most knifemakers don’t even understand what toughness is so it can be really easy to cloud the issue. Example- bending or flexing in a vice is NOT a measure of toughness, and yet it is almost universally described as such by the knifemaking community. Gradual loading like this measures strength/ductility via the steels tensile and compressive or shear strengths. Toughness is the ability to handle sudden loading, to which the slip mechanisms in steel react very differently than in gradual loading. So here I can say that the video is in the ballpark. Probably because of where it was done, I couldn’t see the Germans getting such a basic concept wrong like here in the states (relax I am pure Irish-American, I just know the Germans). So we have the concept correctly demonstrated but the demonstration really yields no data to work with. How many foot pounds did each blow deliver? How does that compare to other steels?

But criticism without any alternatives or suggestions is nothing more than carping. If I wanted to demonstrate the same concept this is how I would do it.

First- data does not exist in a vacuum, if you wish to say something is “tougher” what does that mean unless you can point to what it is tougher than. Find a steel that is established to be tough and is known for it, L6 S7 etc… Prepare both your demo steel and the chosen control for standard Charpy impact samples and heat treat both to the same HRC in a typical knife hardness range.

Run around 5 Charpy V notch impact tests and record the numbers. You now have actual data, in the form of quantifiable and comparable numbers, measuring the specific property you are studying. It takes a lot more work and patience but the results mean something, and they mean something everywhere from an internet forum to a doctoral thesis.

Not everybody has the proper equipment or the time to do proper testing, and often we can get the idea from well-done improvised home testing. As I said, at least this demonstration actually dealt with the property claimed, which is more than most tests I see. But far too much bad information has been passed on and reinforced in the American knifemaking community by home spun “tests” that often are no more than parlor tricks to play on existing beliefs or perceptions.
 
yeah, i guess toughness was bad choice of words. I posted the video because i thought was a hoot, especially since the first half is examining the coupon and measuring its hardness. I was surprised that the coupon was not bent, dented, or broken. it would be nice if someone had all the good toys for testing, a Charpy machine, rockwell and vickers hardness testers, a CARTA machine and a good microscope and instead of a hammer-in had a test-in.
I bought some of this steel to make test knives with because it is the closest to the sacred "Blue Label Steel" from Hitachi that is hard to find and very expensive. the goal, thin blades of high hardness >Rc62, fine edge(total angle <20degrees) that will hold an edge and not chip or break.
 
scott.livesey said:
the goal, thin blades of high hardness >Rc62, fine edge(total angle <20degrees) that will hold an edge and not chip or break.
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Scott, in my experiences and others' as well...............W2 is easily capable of meeting your above goal, as is 80CrV2. And maybe cruforge V would make the list also but I'd need to experiment more with it.

Not to demonstrate strength or toughness or anything else, but rather to look at grain structure, I've found fully hardened, completely UNTEMPERED, as quenched coupons of 80CrV2 remarkably difficult to break in a vise hitting them with a hammer in the same manner as in the video. So much so that a couple of my bladesmithing buddies didn't really believe me. Until I took some of the coupons to their shop and we did it there too. :)

I don't know why and I don't believe it proves anything about a finished knife. Just saying that I've seen some coupons that were pretty tough to break.
 
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the only issues i have with W2, CruforgeV, and 80CrV2 is finding it 1/8" thickness or less. That is main reason most of my work is in O-1. I do stock removal, and do kitchen knives, so even 1/8" is thick except for large cleavers. I used some of Alpha's 1080+(their name for 80CrV2) and was very happy with it, but they dont carry thin stuff any more. I know W2 will make a good blade, I wanted to use a steel with close to the same chemical make-up as the "sacred" blue label, cause there are customers out there who are impressed with that. sorry to have led us off the main topic of this area. i like 80CrV2, O1,O2, and 1.2519 because it all heat treats at same temperature, needs same kind of quenching oil, tempers at about the same temperature, and i have had few issues with post heat treat warp.
 
My experimenting with steels suggests that many people temper to lower hardness than is needed. We are making knives here, not pry bars, or leaf springs! I have had no difficulty with O1, W2, 52100, 15N20, or AEB-L at Rc62 in general use. When I see Rc58/59 advertised in a skinner or EDC, I think of the performance left on the table. I think Rc60/61 is plenty safe with these steels.

Edit: Scott: 52100 makes an exceptional kitchen knife, among the best available, and Aldo carries it in thinner stock. I have used 15N20 as well, and if at Rc62 or higher, it actually holds an edge quite well, not like the higher alloy steels, but it keeps a stable thin edge because of the nickel in it.
 
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scott.livesey said:
yeah, i guess toughness was bad choice of words...
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No, in this case, sudden loading with a hammer, toughness is exactly the correct word, just there is no specific data represented. I could give you two packages of different sizes and have any number of people guess which one feels heavier, but until we put them on a scale, all we have are guesses and feelings about the weight of each. Mr. Doyle does bring up a very good point, I have really nailed the heat treatment on several simple alloys before that caused them to bounce a serious hammer blow to break them untempered. Fine grain size and fine carbide distribution will do that, even more effectively than the initial chemistry. I have even had some that required notching and serious sledging while supported on each end like a vertical Charpy test. It is a miserable and messy way to do it because of the energy involved, pieces fly like bullets into all sorts of hiding places across the shop. In a similar fashion I have demonstrated grain refinement via thermal cycles in my classes where the initial overheated steel can be broken to reveal the enlarged grain size by just clamping it in a vise and lightly pulling on the other end. But after a couple of proper cycles the only way you are going to break it to reveal the grain is with sudden loading with a hammer. I normally make a notch in the anvil edge while hot so that we don't have as many of those projectiles in a room of students.
 
Warren Krywko said:
My experimenting with steels suggests that many people temper to lower hardness than is needed. We are making knives here, not pry bars, or leaf springs!...
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The vast majority of edge deformations/failures that I have examined, with and without magnification, tend to be plastic in nature (metal deformed like it was too soft for the force it encountered) telling me that what you are saying has a lot of merit Warren. Early on when I saw this I started playing with higher hardness in the same edge geometries and was quite surprised at how hard I could keep things and still not get brittle type failure; like in the 60's HRC, not the 50's.
 
Sorry to further derail the topic.......but a quick check just now shows that Aldo has w2 in 1/8" bars right now and Chuck Bybee at Alpha has some 1/8" 80CrV2 in stock right now also.

Now, back on track......I agree with Warren and Kevin. I try to leave my blades of all types as hard as possible. And my edges are thin. I made a bowie recently that had a .015" thick edge before convexing and I kept the tempering temp well below 400F. It held up surprisingly well to even pine knots. The blade was 1075, by the way.
 
Kevin, I had some problems when I started out with chipping, and I cracked two blades. These events were connected to poor heat control and improper quench mediums. Once I was able to get better control over the heat treat, I could start experimenting through controlling different variables, and with grain refinement/proper quench, the steel could handle a lot more than was suggested by my earlier readings. Based on your suggestions, I have been sticking to a few steels, and learning them better, rather than trying a bunch of steels with mediocre heat treats. :)
 
Kevin R. Cashen said:
In a similar fashion I have demonstrated grain refinement via thermal cycles in my classes where the initial overheated steel can be broken to reveal the enlarged grain size by just clamping it in a vise and lightly pulling on the other end. But after a couple of proper cycles the only way you are going to break it to reveal the grain is with sudden loading with a hammer. I normally make a notch in the anvil edge while hot so that we don't have as many of those projectiles in a room of students.
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Where do I sign up? Sounds like my lesson on alkali metals that climaxed with the lights off and dropping a chunk of pure potassium into a container of ice water which resulted in a two foot tall column of smoke and flame. in a lighter vein, "Pure Irish-American" sounds like an oxymoron although i guess i am in the same category, my dad came over from county cork at age 4 while my mom's family can trace themselves to folks on the mayflower.
again, i posted the video because i thought it was a hoot. i realize hardness and toughness are just pieces of the puzzle, that to be properly utilized they must be married to good blade shape and bevel.
 
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