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Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by hammertime99, Jan 8, 2015.
"Geometry determines 'cut'. Heat treatment determines 'how long' it will cut."
Not even with the addition of alloying elements?
Good straight talk on metals.
We appreciate ya, Stacy.
Metal ain't molecular, it's crystalline!
Sorry, Stacy, I saw the beret, and I recall a picture of you in a beret, white beard. I thought....."There's Stacy"!!!!!! And from the article...."Soft steels, unfortunately, cannot be sharpened to as thin an edge thickness as harder steels (see Razor Edged 1 for more information on this), and most certainly suffer from edge folding, breaking and wear much faster than hard steels. Thus, smiths use various techniques to harden the steel."
That is what I have heard. Soft steels cannot be sharpened to the same level as harder steels. The soft apex just being folded over and over, never stabilizing, because it's too soft. Geometry cuts and heat treat determines how long, for sure, but I don't see Roman's axiom coming into play here.
In an practical way, you are right. In a technical way, you aren't. It would take different sharpening methods to put a zero edge on an unhardened blade, but it could be done. But, that is a debate that is different than the main point I was making. I digressed unnecessarily.
My point was that the different between hardened blades at Rc 64 and Rc 59 will make no change in the sharpness....only how long it will stay sharp. The second point was that for many uses, the thought that "harder is better" is false. Too hard can cause the blade edge to fail faster in harder usage.
Excluding Mercury and other glassy (Amorphous) metals.
I ain't a metallurgist but I'm thinking that some of the elements used in the various steel alloys, Silica, etc. will change the crystalline lattice structure of the knife's blade structure.
Is this not so?
Are all the added alloy elements included into the basic crystalline lattice structure? Maybe someone can jump in to this discussion of knife steels.
Hey Stacy, thanks for the very detailed write up on this. You have definitely written it in a way that is easier to read compared to a lot of other stuff out there!
Question for you. What elements play the biggest role in determining grain size? And where does a simple carbon steel fall; is that the largest or default size that everything else would be compared to? From a knifemakers perspective anyway.
Different elements tend to congregate in different places. Most of the common alloying elements in steels will fit into the regular iron atomic arrangement in a substitutional fashion. The arrangement will largely be the same, but there will be say a chromium atom where an iron atom would normally be. Some elements tend to be found in the carbides. They will form their own unique carbides, like tungsten or vanadium carbide, or they will substitute for iron in iron carbide/cementite. In these cases, they can be considered molecules, but it's not that clear always, particularly if one leaves steels. And just to be a picky SOB, silica is silicon dioxide, SiO2. It's definitely found in steel, as silicon is an element added to deoxidize the molten steel. Again, just being picky. For metals, generally speaking, they are not molecular in nature, but there are exceptions to everything. I'm not certain if carbides are considered molecules or not. The bonds might be metallic in nature. I have not looked into it.
Angus7us, I'm not Stacey, but hopefully he won't mind me taking a stab at your question. Unfortunately, I can't give a very clear cut answer. The elements have various effects on grain size, and generally speaking, all of them tend to slow down grain growth. One of the best is Aluminum. It's added as a deoxidizer to the the steel melt. The oxides it forms are extremely fine, and these small oxide particles slow down grain growth very well. The reason my answer is not so clear cut, is the steel processing has a huge effect on the grain size. Without knowing that, it's not really practical to rank how effective the elements are. They also work in different ways, sometimes with the same element. For instance, chromium dissolved in ferrite will slow the rate of grain growth. Chromium carbide will also slow it down, particularly if the carbides are very small. However, I was recently reading of plain carbon steels with extremely small grain sizes, 2 micron and less. These used iron carbide as a barrier to prevent grain growth, though they were processed at relatively high temperatures. There were no other elements added except a lot of carbon. These had 1.5% carbon (a 10150 steel if you will) or more in some cases.
Thanks Stacy! I figured we were are on the same page, you're just further down, reading faster than me!
Thanks Me2, great information. It is a complicated process with myriad variables.
I left out a factor in design and use - MOMENT ( moment of force, moment of inertia)
In physics, moment of inertia is the resistance to change in an angular velocity along a rotational axis in reference to the position of the axis. ( I think I got that right?)
What all that means to knife design is that the way a knife is made ( mass distribution and placement in reference to the center of rotation) will determine how hard it chops and also how straight it cuts. The ways to increase or decrease any rotational effects is to move the axis closer or farther in reference to the point of rotation. Changing the handle length, blade shape, and blade width will all affect this.
That is why a tip heavy chopper will cut deep into a log, a wharncliffe will cut straight into a piece of rope, and the tip of a skinner will follow any slight movement of the hand.
This resistance to change in velocity is also a matter of change from static position ( holding the knife still). If the blade is well balanced and the point of rotation is properly placed, the knife or sword will go into motion with minimal energy applied by the hand (fencing foil or fillet knife). These blades are described as "light in the hand". That is why Zorro could cut the buttons off a ladies dress and slit her corset strings without harming the fair maiden at all. Conversely, a tip heavy behemoth like a Claymore will be hard to get moving, inaccurate in the swing, but strike with a greater amount of energy being delivered to the struck object. That is why the Scotts could cut a man in half.
Thanks Stacy. Good info but to fully understand this I need a picture.
thanks for the great posts. easily understandable for the layman (like me)
Leaving aside, for the moment, speculation upon just why the hot blooded Spaniard chose a weapon particularly suited to disrobing fair maidens, while the dour Scot got similar pleasure from chopping another man in half, with a mighty roar....