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. Turn the gas valve to adjust the flame to a small cone shape. The 4 steps you NEED to know. How difficult it is to flex a knife is controlled primarily by the geometry of the knife, in particular the thickness of the steel. Not knowing what steel is used (0-1, D2, etc. 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. So steels like 26C3, White #1, Blue Super, etc. 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. 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. NordicTrack wants to give you $7,500 toward your dream adventure. This has some truth to it as knifemakers who use a subpar heat treatment will certainly have subpar performance. So if the metallurgists were designing heat treatments for one specific application they would be dealing with many customer complaints. Whichever side snags your nail is the one with the wire edge. No heat treatment can turn 1095 carbon steel into a stainless. 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. Low Alloy and Low Technology Heat Treating Myths. [1] X Research source Larger flames produce less heat while smaller flames produce a higher heat. We asked five pros how they made it work and what it takes to make a living in the outdoor industry "in real life.". Also, the center of the blade’s thickness will naturally reach the temperature later than the surface, meaning that the soak time is shorter at the center. 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 . 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. Some knife users or makers report happily that their knife edge rolled in use as evidence of its good toughness, but it is mostly evidence that the steel wasn’t hard enough and/or the edge geometry wasn’t robust enough. 10. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. This article provides some insights and workarounds for one of the most vexing problems you will encounter when sharpening a knife — wire edges. Wicked Edge/Edge Pro style systems are much more finicky, since they have so many more adjustments and parts. 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. ), it is hard to say how much hardness is lost. Recommended heat treatments often provide longer hold times at lower temperatures where significant grain growth would take a very long time. [1] Cui, Wen, David San-MartÃn, and Pedro EJ Rivera-DÃaz-del-Castillo. Hardening â Holds a sharp edge Hardening a knife makes it hold a sharp edge better. 2. I can only respond with what works for me. I think enough stabilization of retained austenite may lead theoretically to great improvement in some low toughness steels . However, the heat treatment can only do so much. But knife sharpening is a bit of a challenge: part ye olde craftsmanship, part geometry, and part voodoo. Safer - a recreated tip is much safer than a broken-off tip. 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. The file works with a similar principle to the Mohs hardness scale, if one material can cut another then it is harder. This one started out along the lines of “even the best steel will perform poorly if given a bad heat treatment,” and that I can’t disagree with too much. Once the strength of the steel is exceeded the knife will keep bending with approximately the same level of force. There are other dangers to using short hold times, such as the heat treatment being much more sensitive to small changes at short times. XXXX steel “needs” or “doesn’t need” cryo. Whether you’re riding solo or bringing along the whole crew, these are the best hitch bike racks to haul your bike to the trailhead. This long piece of steel is so you can bring up the temperature of your quenching oil. 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. The torch should ignite after a few tries. Quench the titanium part in a suitable quenching media: a water bath or air for alpha-beta and beta titanium alloys, and an oil bath for alpha alloys. By signing up, you agree to receive emails from GearJunkie and Helux. Some knifemakers mistakenly state that when the steel is nonmagnetic that means that the Curie point has been reached, at about 1420°F. Strops should be part of any sharpening regime, and they are especially good at knocking down and erasing a wire edge. 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. You can read more about Curie in this article. I have suggesting modified tempering routes of secondary hardening steels : You can see a wire edge with your naked eye, but if you don’t know what to look for, that’s not helpful. The quenching medium I used was old motor oil. That is one way of doing it, yes. This gives is a great almost mirrored look. Knife Making - How To Heat Treat A Knife | Super Simple DIY heat treating. You can read more about all of these effects in this article on flexing and bending. I found this with my own experiments of AEB-L as in the previous plot. Flooding the knife with coolant during grinding is the life of a knife steel. 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 Your email address will not be published. I hear some knifemakers say that you should ignore information in steel datasheets or the ASM Heat Treater’s Guide because those recommendations are for “blocks of steel several inches thick” or just generally referring to the “industry” boogeyman that means the heat treatment doesn’t have anything to do with knives. However, they are no easier to achieve good properties than high alloy steels. Below is an example from our 52100 heat treatment study that shows the drop in toughness and improvement in hardness with cryo: 7. Thinner knives can be flexed much further without exceeding the strength of the steel, even with identical heat treatment. Once your knife is properly hardened, you should be able to run a worn file down the edge and have it skate over the surface. 1. [2] Lement, Bernard S. Distortion in tool steels. More fun - a smooth edge without bends or chips, which is ⦠Of course, Wicked Edge/Edge Pro sharpeners are frequently used by knife aficionados to put really sick mirror edges on their customs, so keep them in mind if youâre looking for something like that. A few strokes on a strop (counting strokes and alternating sides) with different compounds will rid you of a wire edge. Put your knife and a poker or some long piece of steel. 11. This puts all of the carbide and pearlite in solution, and achieves a consistent grain size prior to air cooling. Another excellent, informative article. These recommendations vary a lot depending on who is giving them but the descending method seems pretty common. Using a file to check hardness is popular because it is cheap. Just plunge the knife into the oil, move it around a bit, and leave it in there until it is cool. “Simple” carbon steels also have retained austenite and are affected by cold treatments. The main benefits of knife repair are: Cheaper - a fully usable knife for a fraction of the cost of a new knife. There you have it. Once the blade has reached its maximum hardness, it's ⦠I explained the mechanisms behind cryo in this article. Yet higher hardening temperatures can be used in combination with liquid nitrogen up to a hardness of about 64 Rc. high on Rockwell C scale) edges are brittle and softer edges are, well softer, but tougher, in that they take less damage and are somewhat more durable, overall at least. 5. If quenching is done in a bath, quench the thick sections first, the cylindrical pieces straight up, and the flat pieces on edge. Metallurgy and Testing of Knives and Steel. 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. It isn’t a light switch that either affects a steel or doesn’t. The other, easier approach is to use strops. Higher alloy steels also have the benefit of easier quenching, either air cooling or plate quenching rather than rapid oil or water quenches. I also performed an edge retention comparison between cryo and non-cryo D2 steel and found no difference apart from hardness, see that here. Your email address will not be published. When using a furnace with a PID and controlled temperatures, high alloy steels are usually “easier” to heat treat. Of course, focusing on any one of these factors at the expense of the others: steel selection, heat treatment, and edge geometry, is a mistake and each should be optimized for the given knife. Using cryo or other cold treatments means you get closer to martensite finish and retained austenite is reduced. To achieve this, the edge is cooled faster than the spine by adding a heat insulator to the spine before quenching. ... At that point, switch to a knife sharpener to finish off the edge. Many folks leave the edge much thicker, but like I said this works well for me. The better a knife retains its edge, the harder it is to sharpen. Files can be purchased which are rated at certain hardness levels though often a generic file is used. Hold a striker over the end of the torch and squeeze it to create a spark. Ok, all the hard work has been done. Less waste - a recycled knife rather than a knife in a landfill. Enter before February 8th for your chance to win. 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. With most low alloy knife steels, the steel transforms to austenite before reaching Curie, and therefore the nonmagnetic temperature is significantly lower, usually somewhere in the range of 1350-1380°F. Tony Sculimbrene is a lawyer and gear-obsessed dad of two who believes a day spent outside is always a good day. Because you've bought a knife with a very hard, stainless steel blade. 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. Below shows the retained austenite for different cold treatments after different delay times at room temperatures. You may unsubscribe at any time. Simply hold the knife with the edge straight up under a bright light (preferably sunlight) and rock the blade side to side and up and down looking for any reflection. 6. I’m sure I am guilty of believing a few. Virtually any knife steel can be heat treated with or without cryo, depending on the hardening temperature that is selected. Most of good heat treating is about avoiding many of the potential issues or mistakes and not about finding the great secret. However, there is a whole industry of cryo companies advertising incredible improvements in wear resistance from cryogenic processing. Cryo is not an on/off thing, and the colder you go the better for minimizing retained austenite. Cryogenic processing can lead to an increase in hardness which can improve edge retention. Cryo improves toughness. Work your way through grits bringing it to the desired finish. Point 10. Using liquid ntirogen with the same hardening temperature gets about 63.5 Rc as-quenched. The Mount Katahdin Knife Edge trail begins right near the summit cairn. 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. The way the knife is being used also matters. 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? If the edge deforms that means the strength of the steel was exceeded. So here are some photos of how to make the knife edge - not difficult, but very neat looking - and- no extra fabric is needed. 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. 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. Keep at it, as practice makes perfect. 9. How to maintain a knife edge with honing. Austenite forms at high temperature prior to quenching. – instead of standard 2h+2h double tempering , using 3h+1h double tempering instead may give better toughness due to lower content of “fresh martensite” which formed from untransformed retained austenite during cooling from first tempering . Low alloy steels are easier to harden without a soak at the hardening temperature, which facilitates hardening in a forge without temperature control. Some of these claims are even found in peer-reviewed journals. The King of Do-All Knives Is Half Price (and Other Amazing Knife Deals). It’s a skill that will be useful for the rest of your life, whether you’re touching up a paring knife in the kitchen or a massive chopper for outdoor work. Excellent… one question. Those high alloy steels don’t “need” cryo either. 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. Backyard bladesmith discovered a new super heat treatment that can’t be matched. A regulator block is used to hold the blade at the correct depth. A wire edge, also called a burr, is the result of sharpening a knife. Heat treatments are designed for industry and don’t apply to knives. Knife sharpening is a fundamental piece of gear maintenance that even translates to the kitchen. Enter your email address to subscribe to this blog and receive notifications of new posts by email. The longer hold times at lower temperatures means both thick and thin parts will result in a similar heat treatment. I see frequently from knifemakers statement like, “I chose AEB-L because it doesn’t need cryo.” Or “Carbon steels don’t need cryo.” Or “Stainless steels need cryo.” This shows a fundamental misunderstanding of what cryo does or doesn’t do. So if the knife is harder than the file that means the file canât cut it. On both sides of the Knife Edge trail lies treacherous slopes of rocky debris. It would take a good edge, but it would shatter. 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. He also authors the gear blog Everyday Commentary. A second heating process known as "tempering" is required. No but they do heat treat it harder than the typical 55 Rc, so it performs a lot better than a lot of other 420HC. Sharpening your knife with the likes of a whetstone uses friction to remove some of the steel and create a new, sharper edge. Become a patron and gain access to awesome rewards including early access to articles or a Knife Steel Nerds mug! https://www.patreon.com/Knifesteelnerds, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). 3. There are two primary ways that a steel can become nonmagnetic: 1) transforming to the “austenite” phase, or 2) by reaching the Curie point. Itâs done by heating the knife to critical temperature and cooling rapidly in a quenching liquid, usually oil. The correct time to temper steel for a knife is after the blade has been formed and shaped but before the final assembly and polishing. Annealed steel is made up of magnetic ferrite and hardened steel is made up of magnetic martensite. 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. And with the social distancing required because of COVID-19, now’s a perfect time to really learn how to sharpen a knife. Below shows martensite content for T1 high speed steel at different temperatures: One other factor to keep in mind, however, is that retained austenite “stabilizes” if there is a delay between the quench and going into the cold treatment. How much does hardness affect the difficulty in flexing? 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. 13. This technique is very dangerous for novices, but glass is exceptionally hard and will definitely kill the wire edge. 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. Another way is to slow cool after the final austenitize to anneal instead. With typical cutting, there is often some combination needed of hardness (strength to resist rolling) and ductility/toughness (resistance to fracture). 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. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. Japanese knives are often made from high-quality but harder ⦠It isn’t high enough to dissolve everything like in a normalize, and isn’t low enough in temperature to lead to the smallest grain size in grain refining steps. Required fields are marked *. For one, it isn’t very precise. I use a lot of O-1 and do my HT with a Oxy. Not sure I am making sense. 12. Clamp the knife down and polish it with emory paper. You can also very carefully hit the edge of the knife on the bottom of a coffee cup or on some stacked cardboard. I’ve once read of a method to get rid of grain boundary cementite (iirc) in forged knives. 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. A honing rod, on ⦠The Curie point is where the ferrite phase becomes nonmagnetic. I flat grind, but when I do a hollow grind I leave the edge at least .025"- .030" thick. The first quarter-mile of the Knife Edge trail leads to Mount Katahdinâs south peak. A file is a good way to check hardness. 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. However, it has become somewhat fashionable to talk about knife performance as entirely (or almost entirely) controlled by the knifemaker’s skill in heat treatment. Finishing the Knife. 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. In general, heat treatments are recommended in datasheets that will apply to the most situations, as the steel may be sold in a range of thicknesses, and used in many different applications. However, there are still issues with using a file. Notify me of follow-up comments by email. 8. Here, we discuss the wire edge, or burr, created while knife sharpening and how to address it. In it, he explains how he uses the edge of a piece of tempered glass (like that found in a car window) to knock down a wire edge as the final step in sharpening. Therefore, using a longer hold time can lead to more consistent hardness both within a single knife and between different knives. This is without covering common mistakes with using files such as checking the knife without removing scale or any decarburized layer first. How the hardness changes things is how far the knife can be flexed before it won’t come back straight. When chopping, the steel is much more likely to act in a brittle matter and chip even when the steel is on the softer side, in that case the behavior is controlled by steel toughness rather than strength. When it comes to maintaining a sharp edge, it all starts with the blade you've bought. However, the intermediate temperatures like 1500°F don’t do a particularly great job of accomplishing either of these goals. It is relatively common to see forging bladesmiths recommend descending temperature normalizing or grain refining cycles, such as 1600°F, then 1550°F, then 1500°F, etc. 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. No where in that book is any information on the traditional knife edge. Wire edges can be frustrating, especially for folks new to sharpening their own knives. The light will only reflect off of flat spots or rounded spots on the blade. My question is, is that quench really necessary or is it nonsense? Well that isn’t entirely accurate, hardened steel actually is about 2-3% less stiff than annealed steel. And as mentioned in the previous myth, superior edge geometry is often what makes a legendary knifemaker have high performance knives, but the super heat treatment is a better story. and if your knives don’t have such a heat treatment they are never going to be as good. Normalizing needs to be performed from relatively high temperatures, depending on the steel, such as 1550-1650°F for 1095 steel. 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. A quench is necessary with very high carbon (>1.1% or so) low alloy steels. So lower hardness means the knife is “bendier” but not more flexible. 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 1925°F. 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.