Anthony: CPM9V would be "the bomb!". Unfortunately, the folks ar Crucible just won't make the stock sizes we need. I have tried everything, including begging.
Honestly, I am starting to think this whole steel thing has gotten a bit out of control. Too many customers just want to know "what steel?" and, if the answer is one of the new whiz-bang alloys, they're happy. So is the maker, who may or not have a clue about heat treating or processing. The problem is that there is SO MUCH MORE to the picture than just the steel. As I've said before (and I probably sound like a broken record), a given steel can be made into a blade that posesses the optimum characteristics obtainable for that type of steel, or turned into a piece of poopoo. ANY STEEL! Generally, the more complex the steel, the more potential to screw it up, or at least have a "hit-or miss" opportunity. This is particularly true of the High Speed category (M2), where heat treatment can be ruined with just a minute or two of soak time. Too much, or too little, and, it's lost.
And, remember-every steel manufacturer is going to add some hype to their products as far as claims go.
The claim to fame for the CPM alloys is Vanadium content and the method of processing. Note that it is also the element, added at just 2.4%, that makes BG42 superior to ATS34 (in addition to superior processing-which should not be discounted). Vanadium makes CPM3V superior to A2 (again-the particle method of production kicks up the mechanical properties).
Comparison of Charpy values and wear resistance values at various hardness levels is interesting, as long as you realize that the Rc hardness is the primary factor that determines how easily the edge will flatten after repeated "push" cuts (no slicing). That is because the compressive strength is pretty well directly proportional to Rc hardness, for any alloy. That is also why I like my steels on the hard side. With that, comes the need to mitigate the loss of toughness as a given steel is used at a higher hardness. Now, here is a quandry: If the tensile strength goes UP with increasing hardness, how come the toughness goes DOWN? It's the reason that you can't buy a bolt that's stronger than 250,000 PSI, because you need some ductility to help prevent catastrophic failure that can be initiated by some small defect-a scratch, spot of rust, internal microscopic defect, etc. This is the reason that aircraft engines aren't held on by one, BIG bolt-you could show it good on paper, but, you can't count on it in reality. Obvious, right?
Instead, you use more, smaller bolts, so each bolt takes less load than it is capable of. Then, you add extra bolts, so that some can fail, and the engine will still stay on. It's a darn good idea!
Glass is about 1000 times stronger on paper than it is in real life-the reason? any scratch-even those so small you can't see them, decreases the strength. The scratch made by a glass cutter weakens the glass so much you can snap it in your hands, with the guarantee that it will break along the scratch!.
So, why am I rambling on? Tensile strength is an ultimate value obtained by testing specially shaped specimens that are loaded in a very precise way. You can't apply a pure tensile force to a knife blade when you use it! You would have to put it in a vise and pull on it. Can you break ANY knife that way? Even Superman BENDS steel to break it, and things loaded in bending break over a wide range of applied loads, usually much lower that the material is supposed to withstand on paper, often due to factors related to crack initiation and propogation, that have a lot to do with things like sharp edges, corrosion, notches and scratches, etc.
Every good piece of aircraft structure is designed to minimize bending loads, because you can't count on the strength of things that are being bent. Good designs load components in tension or shear, where you can count on coinsistent performance to known stress levels.
So, when you stick a knife in a log and bend it, you are on shaky ground. When you twist it while bending it, it's even worse. If you want to use a knife this way, look for one with rounded edges, and smooth transitions between thick and thin areas. And, don't pry with a rusty knife!
And, whether it bends, chips out, tears or whatever, it's going to be ruined, or at least require a good reconditioning. Use a knife to CUT, and you've none of these problems. My advice: Look for a great piece of steel, PROPERLY heat treated, CRYO treated and MULTIPLE tempered, that has a reasonable proportion of thickness to length, and a grind that matches the expected level of abuse. If you have this, you can sheak up a point or two higher, and get more wear resistance and less risk of edge flattening, without having to worry too much about chipping (particularly with the CPM alloys)
Enough for now!
RJ Martin
