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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
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#1
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1075 questions
I have been performance testing the differentially hardened 1075 blades I have been making and have a few questions about what my expectations should be. I can routinely perform a 90 degree bend but it is a one way trip. I lose the portion held in the vise on the return, whether that portion is the tip or the next section up after I have broken the tip off. The grain seems to be uniform in the hardened portions on most of the blades, however there is a definite transition zone in the core on many where the grain on the clay backed portions is noticeably larger than the grain on the fully hardened portions. I do not see a way to homogenize the grain when pursuing the differential hardening and am concerned that his process may in fact produce a blade of inferior quality over a fully hardened specimen that is properly tempered. Your insights would be much appreciated.
Last edited by Jon Kelly; 09-08-2014 at 06:23 PM. |
#2
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Jon Kelly...I personally do not choose to differentially harden my blades. Unless your sole objective is to create a hamon, I see no advantage.
If you do have a gradient in your grain structure, then in my opinion that is proof of a gradient in the quality of the blade. Whenever I make a knife, I through harden the entire blade from edge to spine. Due to the variance in thickness, I suppose there may be a slight difference in the hardening, but...whenever I have tested my blades I usually get a grain structure that is similar to that of a piece of broken porcelain....and I have never had a blade fail during actual use. My personal objective is to get the smallest possible grain structure throughout the entire blade. For a knifemaker to intentionally cause a part of the blade to be softer and tougher is to intentionally make an inferior knife. My through-hardened blades are plenty tough, and I am certain that with enough abuse they could be made to fail...but the same could be said of any blade made by anybody. A hamon can be an attractive feature of a blade...but it in no way adds to the quality of the blade....It does say something about the bladesmith's ability to differentially harden the blade, but beyond that...where is the advantage. If you are in pursuit of an ABS JS or MS certification, and your knife must withstand a 90 degree bend test, then you better know how to differentially harden a blade...but for a blade that is intended to be used...what is the point. |
#3
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I would agree with Ed to a point, the differential temper to get a hommon will make a weaker blade. If the steel is stock removal it must be annealed properly, if you start with a bad grain structure you end with one. If forged you must follow good forge theory to prevent grain growth. If it's an indestructible knife your after then learn the softback draw. If you want one that can be bent back and forth then you are using the wrong steel to begin with. You need alloys that have nickle content like L-6. I pulled my 65lb vice from the work bench with a 8" clip point made from L-6. It flexed may be 2" off center before the vice gave then went back strait.
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#4
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My sole objective has been creation of the Hamon, however I do not like what I am seeing internally. Since I do not want to make knife shaped objects I took six blades to destruction over the weekend and what I learned was 1075 with hamon as made in my shop all failed the 90 degree flex, which probably doesn't mean squat, lol. Perhaps this falls within the reasonable limits of this steel and I am simply expecting too much. Regardless I think I will forgo the Hamon and pursue a through hardened blade.
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#5
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Just be aware that if the blade is too thick the 1075 will not harden all the way through. What this means is that you may end up with a blade that will harden only a certain distance in from the edge, probably to where it's only about 1/8" thick, and then thicker than that pearlite will form. This also will depend on grain size too with fine grain restricting the depth of hardening.
If you want a blade to harden all the way to the spine you might have to try a deeper hardening blade steel such as the 1084 or the 80CrV2 that The New Jersey Steel Baron carries. They have a few more alloying elements than regular 1084 or 1080 do. Something like 5160 or 6150 are deeper hardening steel with a lower carbon content to increase toughness. Some people get the impression that a differentially hardened blade is the sign of a superior blade because the ABS requires it in it's performance test. It's not. It only shows that the maker can make a blade that will bend 90? and not break completely through. Be aware also that it's not expected that the blade straighten back out. There are plenty of knife makers who consider a knife that can be driven into a tree and take their full weight to be better. It's all a matter of what each maker want's out of his or her knives. Doug __________________ If you're not making mistakes then you're not trying hard enough Last edited by Doug Lester; 12-22-2013 at 07:22 PM. |
Tags |
abs, art, bee, blade, blades, choose, edge, forge, forged, hamon, harden, how to, knife, knifemaker, knives, made, make, making, steel, stock removal, temper, vise |
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