Lower hardness means the knife is more flexible. No heat treatment can turn 1095 carbon steel into a stainless. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. This has been applied to some extent to several popular knifemakers though perhaps the best example is the late Frank J. Richtig who I wrote about here. The quilts just don't look right to my eye - the binding immediately marks them out as not British. Preamble - Once you get into the knives and start picking up basic knowledge about steels, Rockwell Hardness, edges and angles, inevitably you come across the statement that hard(i.e. High alloy steels, on the other hand, can usually be austenitized over a rather wide range of temperatures because the carbides dissolve over a wider temperature range, this means that hardness changes more slowly with temperature changes, and the higher carbide content also means that grain growth is slower. However, higher hardness levels can be achieved when using cold treatments, see the chart for AEB-L below, where the minimum temperature is labeled as “LN2” (cryo), “freezer” (a household freezer), or “room temperature” (no cold treatment): You can see that the hardness peaks around 62 Rc with no cold treatment, using a hardening temperature of 1925Â°F. Some knifemakers mistakenly state that when the steel is nonmagnetic that means that the Curie point has been reached, at about 1420Â°F. Light a propane blow torch to use as a heat source. There are other dangers to using short hold times, such as the heat treatment being much more sensitive to small changes at short times. See the chart below for carbon and chromium “in solution” during holding of 52100 at 1545Â°F: You can see that the change in C/Cr in solution is very rapid within the first few minutes, and trying to target a specific hardness would be challenging if you are trying to hold for very short times, especially under 5 minutes. I wrote about what is possible in heat treating and what isn’t in this article. Next, while holding the steel's grip with your non-knife hand, place the heel edge of your knife onto the steel. Doing this carefully will reveal a wire edge when your nail hangs up at the edge. Home Forums > Knife Specific Discussion > Maintenance, Tinkering & Embellishment > hard steel how to sharpen impossible knives Discussion in ' Maintenance, Tinkering & Embellishment ' started by simpleguy , Aug 4, 2009 . Some of these claims are even found in peer-reviewed journals. – second modification : instead of double or triple tempering why not just tempering steel at secondary hardening range for 4 hours for example then following it by tempering at low temperatures “200-400Â°F” to stabilize retained austenite & temper any fresh martensite ? The image below shows measured edge retention of 154CM knives with different edge angles so you can see the vast difference in measured performance (higher number means more cardstock cut). “Simple” carbon steels also have retained austenite and are affected by cold treatments. Using a file to check hardness is popular because it is cheap. If the edge deforms that means the strength of the steel was exceeded. When the martensite finish temperature is below room temperature there will be some amount of “retained austenite” which isn’t transformed to martensite leading to lower hardness and other effects. Above that temperature the hardness drops because of excess retained austenite, usually amounts greater than 15-20%, which is undesirable. Ok, all the hard work has been done. Some knifemakers are afraid of holding too long at austenitizing temperature because of concerns about grain growth. As described previously, martensite finish temperatures change for different steels and hardening temperatures, and the closer you get to martensite finish the lower the retained austenite. A honing rod, on â¦ The microstructure can be pretty inconsistent after forging, so normalizing helps to even things out, hence the name normalizing. Finishing the Knife. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. You have the two sides of the blade coming together at a point, and riding along that point for the entire length of the blade is a small, toothy section of very thin steel raised up from the main edge. More fun - a smooth edge without bends or chips, which is â¦ Once the strength of the steel is exceeded the knife will keep bending with approximately the same level of force. Another excellent, informative article. This has some truth to it as knifemakers who use a subpar heat treatment will certainly have subpar performance. Recommended heat treatments often provide longer hold times at lower temperatures where significant grain growth would take a very long time. I have always steeled higher than that of the honed edge thus creating a micro bevel making the knife both sharp and strong enough to withstand a hard days graft. As long as we work to understand the mechanisms at work and to learn from reliable experiments rather than anecdotal observations we can continue to kill more myths. Thanks to Lee Rothleutner and J Hamm for becoming Knife Steel Nerds Patreon supporters! NordicTrack wants to give you $7,500 toward your dream adventure. It isn’t a light switch that either affects a steel or doesn’t. In general, the difference between any “good” and “super” heat treatment is going to be relatively small. I have a feeling that this article isn’t going to make much of a dent in the sharing of myths but I’m doing my best. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. I reviewed the literature here. So BOS heat treating doesn’t give my Buck 420HC the wear resistance of M390? ... At that point, switch to a knife sharpener to finish off the edge. Clamp the knife down and polish it with emory paper. Metallurgy and Testing of Knives and Steel. Now this doesn’t mean that every datasheet is perfect; the heat treatment may be produced for the “lowest common denominator” that could be further optimized for knives. 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Flooding the knife with coolant during grinding is the life of a knife steel. Then take a sharp file for metal working and sharpen an edge on it not to thin of an edge and not to thick of an edge. When it comes to maintaining a sharp edge, it all starts with the blade you've bought. A lot of shared myths come from a misunderstanding of how the steel is transforming during different processes and what the goals are of each step. However, the heat treatment can only do so much. Japanese knives are often made from high-quality but harder â¦ Your email address will not be published. The other, easier approach is to use strops. From here, the trail slowly descends as the ridge bends around the basin. A freezer doesn’t do anything; at least dry ice temperatures are necessary for cold treatments. Here is a chart of retained austenite contents and hardness values achieved with and without cryo with low alloy steels: Now just because the retained austenite can be reduced with cryo doesn’t mean that you have to do so. A quench is necessary with very high carbon (>1.1% or so) low alloy steels. So here are some photos of how to make the knife edge - not difficult, but very neat looking - and- no extra fabric is needed. So the file ends up being a check for a heat treatment that completely failed (did not harden), but is not particularly useful for dialing in heat treatments or for checking consistency. Less waste - a recycled knife rather than a knife in a landfill. Hardening â Holds a sharp edge Hardening a knife makes it hold a sharp edge better. The formation of martensite is measured with a “start” and “finish” temperature and the closer to the finish temperature you reach the more martensite forms and the closer to the maximum hardness you will achieve. 5. I have suggesting modified tempering routes of secondary hardening steels : If you are doing a double sided knife make sure that you do an equal amount of filing in both sides or it won't sharpen right. Using a Coffee Mug for Quick Results Place an old coffee mug upside down so that the bottom of â¦ This practice may have started with a kernel of truth to it, as a normalize is performed from high temperature, and grain refinement from lower temperatures. Tempering â Increases toughness I use a lot of O-1 and do my HT with a Oxy. If you for example hone your knife at 21 degrees and steel at exactly that same angle in my experience the knife will dull very quickly immaterial of how well you polished the edge to. Sometimes edge deformation/rolling is misinterpreted as chipping and the knife user incorrectly believes that the steel has insufficient toughness when in actuality insufficient hardness is the issue. I think enough stabilization of retained austenite may lead theoretically to great improvement in some low toughness steels . Knife sharpening is a fundamental piece of gear maintenance that even translates to the kitchen. Itâs done by heating the knife to critical temperature and cooling rapidly in a quenching liquid, usually oil. Your email address will not be published. A regulator block is used to hold the blade at the correct depth. Wicked Edge/Edge Pro style systems are much more finicky, since they have so many more adjustments and parts. 9. Make sure you get out of the quench and straight into the cold treatment no matter what steel and heat treatment is being used. Sometimes datasheets will provide different temperatures or hold times depending on the thickness of the piece, but that is more of an economical feature (don’t waste any more time than necessary) than one that is required for performance. Here’s a very pronounced wire edge (I worked the edge specifically to emphasize the wire edge for photo purposes): You will undoubtedly feel a wire edge or burr when you drag your nail toward and off the edge of the knife. Lower temperatures typically mean a smaller grain size. You can see a wire edge with your naked eye, but if you don’t know what to look for, that’s not helpful. Turn the gas valve to adjust the flame to a small cone shape. Those formation temperatures are controlled by the steel composition and also the heat treatment, as higher hardening temperatures put more carbon and alloy “in solution” to affect the martensite formation. Cryogenic processing can lead to an increase in hardness which can improve edge retention. Many specific examples could be given of the heat treatment parameters that knifemakers are worried about in datasheets, but one is hold time at the austenitizing (hardening) temperature. An unlabeled file might be around 62 Rc or so and therefore if the knife is higher than 62 Rc (which most low alloy high carbon steels should be after quenching before tempering), then the file will “skate” the knife rather than bite into it or leave scratches. ), it is hard to say how much hardness is lost. The way the knife is being used also matters. This puts all of the carbide and pearlite in solution, and achieves a consistent grain size prior to air cooling. Most of good heat treating is about avoiding many of the potential issues or mistakes and not about finding the great secret. In that way, this is not a myth. The quenching medium I used was old motor oil. The better a knife retains its edge, the harder it is to sharpen. There you have it. However, there is a whole industry of cryo companies advertising incredible improvements in wear resistance from cryogenic processing. Annealed steel is made up of magnetic ferrite and hardened steel is made up of magnetic martensite. So if the knife is harder than the file that means the file canât cut it. How the hardness changes things is how far the knife can be flexed before it won’t come back straight. Files can be purchased which are rated at certain hardness levels though often a generic file is used. I reviewed the literature in this article. Not sure I am making sense. It would take a good edge, but it would shatter. You may unsubscribe at any time. more transformed retained austenite after first tempering means less fresh martensite which should means higher toughness . It also doesn’t help much in tempering to see what the final hardness is, as the final hardness is likely lower than the file. If lower hardness is desired or if grain growth is discovered at a given hardening temperature, simply reduce the temperature and maintain a sufficient soak time. Tony Sculimbrene is a lawyer and gear-obsessed dad of two who believes a day spent outside is always a good day. When using a furnace with a PID and controlled temperatures, high alloy steels are usually “easier” to heat treat. A wire edge, also called a burr, is the result of sharpening a knife. Below is an example from our 52100 heat treatment study that shows the drop in toughness and improvement in hardness with cryo: 7.  X Research source Larger flames produce less heat while smaller flames produce a higher heat. How much does hardness affect the difficulty in flexing? The first quarter-mile of the Knife Edge trail leads to Mount Katahdinâs south peak. You would need to grind all color left from heating out of the finished knife to be sure that the knife will retain its edge as long as possible. Here, we discuss the wire edge, or burr, created while knife sharpening and how to address it. These recommendations vary a lot depending on who is giving them but the descending method seems pretty common. For understanding those aspects better I recommend clicking on a few of the links in this article to better understand topics like annealing (Part 1 and Part 2), austenitizing (Part 1, Part 2, and Part 3), quenching, and tempering. He also authors the gear blog Everyday Commentary. Knife Making - How To Heat Treat A Knife | Super Simple DIY heat treating. Open the gas valve near the base of the torch. In this case half of the retained austenite that transforms with liquid nitrogen can be eliminated with a freezer, but only if there is no delay at room temperature. Imagine a sharpened knife edge zoomed way in. That is one way of doing it, yes. The end of winter is a good excuse to do some gear maintenance. 6. The Mount Katahdin Knife Edge trail begins right near the summit cairn. Now that you've sharpened your knife, use a honing steel weekly to keep the knife's edge perfectly straight (don't â¦ In tempering, the steel is heated to a much lower temperature, and it softens and becomes more ductile (pliable). I found this with my own experiments of AEB-L as in the previous plot. Somewhat of an extension of the above myth is the legend of the knifemaker who has a super ultra heat treatment that leads to double the toughness, triple the edge retention, etc. Grain refinement can then be performed at lower temperatures, just above austenite formation such as in the range of 1375-1450Â°F. However, you can do the same with high alloy and stainless steels with appropriate selection of austenitizing temperature.
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