A honing rod, on ⦠The main benefits of knife repair are: Cheaper - a fully usable knife for a fraction of the cost of a new knife. Virtually any knife steel can be heat treated with or without cryo, depending on the hardening temperature that is selected. 3. Point 10. Strops should be part of any sharpening regime, and they are especially good at knocking down and erasing a wire edge. There are other dangers to using short hold times, such as the heat treatment being much more sensitive to small changes at short times. 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. In that way, this is not a myth. And I would argue that the single most important factor for knife performance is the edge geometry rather than the steel selection or heat treatment. How difficult it is to flex a knife is controlled primarily by the geometry of the knife, in particular the thickness of the steel. Knife sharpening is a fundamental piece of gear maintenance that even translates to the kitchen. Your email address will not be published. Use a knife like you ought to use a knifeâthat is, often and hard, and sharpened frequentlyâand youâll need to reprofile the edge as you hone away more and more steel. I also performed an edge retention comparison between cryo and non-cryo D2 steel and found no difference apart from hardness, see that here. Tempering at higher temperatures results in a softer blade that will be more durable and less likely to snap off, but will not hold an edge as well. 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 . The problem with the edge is that, while it’s exceptionally sharp, it’s also exceptionally weak, folding or flopping over from one side to the other with almost no pressure. It doesn’t. However, grain growth is controlled by both time and temperature. 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. Well that isn’t entirely accurate, hardened steel actually is about 2-3% less stiff than annealed steel. 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. Turn the gas valve to adjust the flame to a small cone shape. However, the heat treatment can only do so much. A wire edge, also called a burr, is the result of sharpening a knife. This puts all of the carbide and pearlite in solution, and achieves a consistent grain size prior to air cooling. The quenching medium I used was old motor oil. Is the grain refinement step around aus temp not usually associated with a quench to set up martensite that is faster to dissolve again so less time is used for the actual sub critical anneal step? See the chart below for carbon and chromium “in solution” during holding of 52100 at 1545°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. [1] X Research source Larger flames produce less heat while smaller flames produce a higher heat. Instead of dropping the heated knife into the quenching medium tip first, submerging the entire knife, the edge quench involves submerging one third to one half of the blade's width (cutting edge first) into the quenching medium. I flat grind, but when I do a hollow grind I leave the edge at least .025"- .030" thick. Your email address will not be published. You can also very carefully hit the edge of the knife on the bottom of a coffee cup or on some stacked cardboard. Another study on 154CM had a more extensive comparison where also no difference was found. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. ), it is hard to say how much hardness is lost. If you can’t prevent the creation of a wire edge by systematically counting strokes or passes and keeping your grind angle consistent, then you need to sharpen with a plan to address the wire edge after it comes into existence. When using a furnace with a PID and controlled temperatures, high alloy steels are usually “easier” to heat treat. However, they are no easier to achieve good properties than high alloy steels. In tempering, the steel is heated to a much lower temperature, and it softens and becomes more ductile (pliable). 5. To test the steel and see if has hardened correctly, take a file and scrape the corner of the file across the knife. Recommended heat treatments often provide longer hold times at lower temperatures where significant grain growth would take a very long time. Many folks leave the edge much thicker, but like I said this works well for me. Hardening â Holds a sharp edge Hardening a knife makes it hold a sharp edge better. Clamp the knife down and polish it with emory paper. Make sure you get out of the quench and straight into the cold treatment no matter what steel and heat treatment is being used. Not sure I am making sense. I think enough stabilization of retained austenite may lead theoretically to great improvement in some low toughness steels . American Society for Metals, 1959. The Knife Edge Ridge. 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. The edge geometry greatly controls the cutting ability and edge retention of the knife and also resistance to chipping and rolling. 2. The first quarter-mile of the Knife Edge trail leads to Mount Katahdinâs south peak. [1] Cui, Wen, David San-MartÃn, and Pedro EJ Rivera-DÃaz-del-Castillo. Excellent… one question. Lower hardness means the knife is more flexible. For example, low alloy steels tend to drop off rapidly in toughness if they are hardened from too high a temperature, see 5160 for an example below which has a significant drop in toughness when using 1550°F. Enter before February 8th for your chance to win. 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. Files can be purchased which are rated at certain hardness levels though often a generic file is used. 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. Thanks to Lee Rothleutner and J Hamm for becoming Knife Steel Nerds Patreon supporters! Cryogenic processing can lead to an increase in hardness which can improve edge retention. Annealed steel is made up of magnetic ferrite and hardened steel is made up of magnetic martensite. A knife that is easier to take a “set” is not more flexible as much as it is just soft. But one mistake people make is thinking that if a little of something is good then more of it must be better and started adding in intermediate steps. 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. That raised, toothy section is a wire edge. 8. Quenching Oil - This is a bucket of oil that you use to quench the knife blade. 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. In that case the center and surface could have significantly different carbon in solution leading to a hardness discrepancy, it can also mean that warping or cracking is exacerbated. But if we were to pick one factor that is the “most important” I’m not sure that heat treatment would be the one. Start by putting the knife in a vise. This is without covering common mistakes with using files such as checking the knife without removing scale or any decarburized layer first. A freezer doesn’t do anything; at least dry ice temperatures are necessary for cold treatments. Work your way through grits bringing it to the desired finish. The longer hold times at lower temperatures means both thick and thin parts will result in a similar heat treatment. Below is an example from our 52100 heat treatment study that shows the drop in toughness and improvement in hardness with cryo: 7. The microstructure can be pretty inconsistent after forging, so normalizing helps to even things out, hence the name normalizing. Put two things in the fire. S90V and S110V are extremely similar, however, S110V is simply a bit harder and a bit better in each category. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. Using liquid ntirogen with the same hardening temperature gets about 63.5 Rc as-quenched. Basically normalize at ~100-150°C above the steels austenitizing temp to dissolve all cementite, then quench it to prevent gb cementite from forming during cooldown. Cryo improves edge retention. Now that you've sharpened your knife, use a honing steel weekly to keep the knife's edge perfectly straight (don't ⦠Differential hardening is a method used in heat treating swords and knives to increase the hardness of the edge without making the whole blade brittle. The end of winter is a good excuse to do some gear maintenance. A quench is necessary with very high carbon (>1.1% or so) low alloy steels. More info belowâ¬ï¸Beginner knife making steel video. 13. I explained the mechanisms behind cryo in this article. ) with different compounds will rid you of a new, sharper edge different than rapid... Set of cycles that does make some sense could be 1600, 1450, 1250°F was exceeded of Making carbide... Carbon ( > 1.1 % or so ) low alloy steels also have the benefit of easier quenching, air! 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