Knife and steel testing

scott.livesey

scott.livesey

Dealer - Purveyor
When talking knives and blade steel, you usually see three terms used a lot. Hardness, toughness and wear resistance. Hardness usually is shown as RcXX and is obtained from a Rockwell C hardness tester. If I test my blade on a calibrated tester and get a value, I should be able to use any calibrated tester and get the same value +/- 1.
toughness and wear resistance are different animals. Part of "toughness" in knives is finding a valid non-destructive test. The Charpy test(good video [www.youtube.com]) that is often referenced on steel maker's websites, is basically putting a piece of steel in a holding fixture then whacking it with a weight on a pendulum. the machine has been calibrated and gives a value in foot pounds or Joules. the sample is destroyed. I would guess you would need to test at least 10 identical(in size, Ht, size and shape of notch,....) samples just to see how big a sample pool you would need to get valid data. and all you really know is the amount of force it would take to break a sample.
static torsion has one end of sample fixed while the other end is turned until sample breaks. again, sample destroyed. don't know how this could relate to knife use. bend test applies weight to center of sample in a fixture, you can see how far sample can be bent and return, bend and stay bent, bend and break.
It is pointed out in Tool Steels by Roberts(pg 63-66) "no impact test has yet been devised that enables comparison of the toughness of the different classes of tool steel." Nicks, scratches, burrs and grinding marks on the surface and notches cut for impact testing can give misleading results with hardened tool steels.
Wear resistance is usually tested by abrasion. the abrasives must be identical. heat treat and weight identical for each group of samples. how sample touches abrasive and speed and pressure it touches abrasive must be identical. weigh sample. for an example let's say a 60 grit blaze belt at 2000 fpm with 10 psi of force holding sample to belt for 1 minute. weigh sample. change belt. new sample. repeat at least 9 times. then repeat with 10 samples of steel 2. steel one lost 11 grams +/- 2grams. steel two lost 15 grams +/- 2grams. conclusion could be steel one has better wear resistance OR steel one is harder to grind.
I guess we could modify the Charpy test so it showed force needed to break sample, but unless I am making armor does the test give me any real world use information? bend tests would be nice if making crowbars. if I am cutting boneless protein, fruit and veg is the abrasion resistance to the carbides in a blaze belt giving any real world info?
any thoughts
scott
 
Fantastic post. These are questions I often ask myself.

Perhaps I am looking at this way too simply, but I don't think laboratory tests are all that useful for knives. It believe those tests are somewhat useful in helping us choose blade steels rather than making a knife from every known steel and then trying to break it. At least if you are familiar with a few steels, having those tests to look at will tell you how that steel *may* compare with a steel you are already familiar with. But, at the end of the day, the only way to know how well a knife holds up is to make one and try it. And even here, geometry probably has more to do with that than the type of steel, aside from things that are easily observed like corrosion resistance and edge holding.

I can't recall ever breaking a knife in my life, even a cheap one. I tell my customers up front that my knives are meant to be slicers. If they want to make firewood, a folding saw is twenty bucks.
 
Good post Scott. Testing is one sure way to know that the steel you are using is best suited for the type of knife you are making. I love testing.
 
I think Scott sums up what most knifemakers learn over time/experience. "Scientific" testing on knives/blades doesn't give any definitive answers/direction, beyond a very small sliver of the pie. There was a time, early in my career when I sought the results of scientific testing, simply because I didn't have enough experience to know any better.

Speaking for myself, as I gained more experience with knives and steel, the realization hit me that I deal with too many variables to place much emphasis on specific scientific tests, and how their individual results impact a knife blade. Steel can vary from batch to batch, grinds differ from blade to blade, as does heat treat, and just about every other aspect/operation that the individual knifemaker preforms. I think that's a big part of the game.... striving for that elusive "perfection", but knowing that we will likely never achieve it.

While scientific testing can help us to better understand our media, and how it reacts to the various inputs from us as knifemakers, I think it's extremely important for each individual knifemaker to to develop their own PRACTICAL standards for quality assurance, whatever those might be. Because of any number of personality traits, levels of experience, or even personal likes/disliked, one knifemaker might place emphasis on hardness, another on geometry, and still others might only care about aesthetics. BUT, over time, I think that most knifemakers arrive at the conclusion that the end product depends on the combination of all aspects/characteristics, and how they are blended to produce the finished product. Eventually, it all falls back on the individual's integrity. I would like to think that every knifemaker does the very best they can, to produce the very best product they can...... the caveat is what the term "best" means to each specific knifemaker.

Having said that, I tend to lump knifemakers into 1 of 2 categories..... Those who produce the very "best" that they can, no matter the amount or time and/or effort involved, and those whom I refer to a "bean counters".....who will only apply a given amount of time/effort towards a given knife based on what they feel they can sell if for.

Back to the subject at hand..... I believe there are two types of testing when it comes to knives.... the scientific tests, that are best used as input to help knifemakers build/improve their knives, and the practical testing, which gives a clearer image of just how well, or how poorly a knife with given characteristics will perform for it's intended use(s).
 
I understand the value of quality. but what to do with makers who make claims like "3V will be anywhere from 1 1/3 to 2 times tougher than A2 depending on the heat treatment" or " If I were to choose a CPM carbon tool steel for a large blade, it would be CPM 4V. IMO, much better then 3V in toughness, edge retention and stability."
 
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I understand the value of quality. but what to do with makers who make claims like......
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There are always going to be those who make this claim, or that claim.... it's human nature. In some cases there are those who's claims are valid....but in today's world, with all the "Arm Chair Experts", it'often very difficult to separate the wheat from the chaff, especially for newer Knifemakers. What I have noticed over the years is that time always catches up with those who make outlandish claims concerning knives. By that I mean that IF the claimant is selling knives, they might sell a few based on "hype", but news, good or bad, travels at the speed of sound in the knife world..... and more times than not, I've seen over zealous "hype", sink the claimant's ship. :)

It's very easy for individuals to read a spec sheet on a given steel, or read a post on some knife forum, and draw a conclusion based solely on that information, and I believe we see a lot of that theses days. What's far rarer is for an individual to actually test their theories before making claims. My advice to anyone making knives is to take EVERYTHING they are told with a grain of salt, until the prove or disprove it for themselves. Concerning those who make claims, let them make the claims. Sooner or later it will catch up to them.

I've often spoken of a Knifemaker's reputation and how important it is..... part of establishing/maintaining a good reputation is to temper the claims one makes about his or her knives, and let the knives speak for themselves.
 
In defense of proper scientific testing

I employ two testing regimens in my shop. Tests that are highly standardized and precise, “scientific” as some would call it, for the evaluation of my steel selection and processes, like heat treatment. The second is practical application of heavy use in the way the knife was intended to function to determine the effectiveness of the final product, i.e. the knife itself.

No piece of lab equipment can give you input on how the knife will work and feel in the hand, and it would be silly to try to put a finished knife in an apparatus designed to work on standardized test samples. However, I have found it to almost be universal human nature to favor data sources that tell us what we want to hear and spurn those that may give us bad news. “Practical” testing with our hands is quick, easy, and within the means of anybody making a knife, and it also can be very easily skewed or interpreted to confirm what we wanted to believe before testing, especially if it is used to evaluate details about our processing that really require more precise analysis.

I often use the analogy of a jigsaw puzzle with a picture we want to see. Proper material testing gives is very accurate and precise data in the form of single pieces of the puzzle, so relying on one piece leaves us simply guessing at the big picture. The real problem with lab type testing is that it is much more involved, tedious and difficult than most people realize or would care to do. Thus, people will attempt it in very unprecise or incorrect ways and when the results make no sense they will reject the concept of such testing. One very common example is the ubiquitous Rockwell test, many people have the testers, but very few are actually using them with any precision, or accuracy. But it makes them feel good to show others that single Rc dimple and say they are doing fine.

On the subject of Charpy, yes it does take some effort and time to develop the numbers, and it must be done on a highly standardized sample (exact dimensions, surface finish, and heat treatment) and thus cannot test knives, or the inherent chemistry of a given steel. But it can assess quite well the impact toughness imparted to a given steel by a particular heat treatment process. At this time, I currently know of only one knifemaker neurotic enough to devote the effort in owning and using their own Charpy tester. You have got to really be into pure material properties and processing, more than is needed just to make a knife.

I can't tell you how many times a year my lab equipment provides answers to other knifemakers on their processing when all of the "practical" methods have been exhausted. And it often involves an answer that no metallurgy text prepares you for because knifemakers do things to steel that metallurgist never considered.

I hear claims of “knife” properties all the time as well, many don’t even make sense, but they do catch the attention of the general public. I have learned when to smile and walk away, or much more of my time would be taken up on much less productive efforts than what I can gain in my lab or out in the field actually using a knife.
 
I believe in testing using scientific methods. I am glad Honda and GKN do torsional impact tests on the steel used for my drive axles, that Crucible and Norseman do hot hardness tests on the drill bits I buy. other than the Carta test, there seems to be no established non destructive tests for knives.
when investigating claims made on forums it is interesting to find the maker pushing CPM x69 steel as toughest and most wear resistant, has a website full of inventory made of x69.
 
Yes, the “greatest steel ever” bandwagons are often driven by biases, more than objectively presented data. I just finished two weeks of teaching and lecturing and once again had to somehow gently break the news to many folks that 5160 is actually a poor choice for a skinning knife. They had no idea, since they had never used a higher carbon/carbide content steel and were dubious of my claims since 5160 makes a nice skinner if all you have ever used is 5160 skinners. I have never said that any of my steels of choice are “best” at anything except matching up with my way of making a knife, and my decision in using them is based solely on that- will this alloy give me what I want with the way that I make knives? Unless one wants to believe in unobtanium, that is the most you can hope for.

Much the same can be said of the processing methods that makers will espouse as the greatest. It is why I cringe whenever somebody asks me for my “recipe” for heat treating a given steel. This “recipe” concept is fostered and fed by the claims of so many makers who are more interested in justifying what they have been doing for years rather than sincerely looking for methods of actually optimizing the materials potential for real knife use. I have no recipes for heat treatment, all I have are pieces of information that can be assembled in ways to best suit the variables inherent in the shop and methods of each maker. Even within my own shop I occasionally get “anomalies” that a recipe would be helpless to deal with, so using the tools and information at my disposal I do my best to identify and compensate for the new variable.

Due to how basic a tool the knife is, we heavily underestimate how infinitely complex making one can be. With mills, drills and other tooling that is chucked into a machine and ran in very set ways, the variables are more easily isolated; cutting speed, feed rate, etc… are all measurable. The human hand chopping, cutting and slicing with a knife on who knows what variety of mediums is about as clear as mud. We really do not give ourselves enough credit that we can meet the demands of totally unpredictable applications as well as we do.
 
scott.livesey said:
I believe in testing using scientific methods. I am glad Honda and GKN do torsional impact tests on the steel used for my drive axles, that Crucible and Norseman do hot hardness tests on the drill bits I buy. other than the Carta test, there seems to be no established non destructive tests for knives.
when investigating claims made on forums it is interesting to find the maker pushing CPM x69 steel as toughest and most wear resistant, has a website full of inventory made of x69.
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It should not be surprising to see a maker tout a wonder steel that is also his choice of knife steel. That doesn't necessarily indicate a lack of integrity as much as it would a naivete about the many good steels being used for knife making.

My eyebrows go up more over the maker that jumps steels without learning one very well. To me, if a customer asked for a knife out of a steel that was a tricky HT and I had never made one from that material before...."No" would be the highest integrity answer I could give....unless losing a sale was weighing in too much. I'm bettin' "No" doesn't happen too often...?

As far as anecdotal testing over scientific testing. Steels with a long industrial history can help in figuring best usage by extrapolating from the wealth of industry data. For me three that I have worked with come to mind...O1, A2, 440C.

When I apply Ed's reasoning on how little material testing matters on the whole of knife/blade making...or the quality/usefulness of the end product, I would have to conclude that blade material choice would also be less of a player than many would think. Proper Heat Treat(proficiency in working with a specific steel), bevel choice, shape/design of blade and handle go much further in making a good knife. This could also mean that minor alloy changes from the various steels du jour is merely straining at gnats. Have you really wrung out the one you're getting ready to discard?

I love testing....everything. adhesives, leather dyes,glues,rivets,stitching methods, grinds on the steel I am learning, finishes on steel, wood, leather. All of this is more intuitive than scientific....but...I pay attention to consistencies. When I can repeat something accurately then I have arrived at an acceptable method. The downside to much testing is more test projects than knife projects....

Just some thoughts...I guess each fella has to pin down what matters and what doesn't....
 
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