Here, we discuss the wire edge, or burr, created while knife sharpening and how to address it. Cryo is not an on/off thing, and the colder you go the better for minimizing retained austenite. This article provides some insights and workarounds for one of the most vexing problems you will encounter when sharpening a knife — wire edges. Your email address will not be published. The 4 steps you NEED to know. The file works with a similar principle to the Mohs hardness scale, if one material can cut another then it is harder. Backyard bladesmith discovered a new super heat treatment that can’t be matched. Sharpening your knife with the likes of a whetstone uses friction to remove some of the steel and create a new, sharper edge. So if the knife is harder than the file that means the file canât cut it. 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. 5. 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. It would take a good edge, but it would shatter. So a descending temperature set of cycles that does make some sense could be 1600, 1450, 1250°F. âTowards efficient microstructural design and hardness prediction of bearing steelsâAn integrated experimental and numerical study.â Materials & Design 133 (2017): 464-475. However, the intermediate temperatures like 1500°F don’t do a particularly great job of accomplishing either of these goals. 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 knife that is easier to take a “set” is not more flexible as much as it is just soft. 1. Ok, all the hard work has been done. [2] Lement, Bernard S. Distortion in tool steels. There are two primary ways that a steel can become nonmagnetic: 1) transforming to the “austenite” phase, or 2) by reaching the Curie point. Knife Making - How To Heat Treat A Knife | Super Simple DIY heat treating. If you go even lower you can perform a subcritical anneal from temperatures like 1250-1300°F. You can read more about all of these effects in this article on flexing and bending. This puts all of the carbide and pearlite in solution, and achieves a consistent grain size prior to air cooling. That raised, toothy section is a wire edge. That is one way of doing it, yes. [1] Cui, Wen, David San-MartÃn, and Pedro EJ Rivera-DÃaz-del-Castillo. Keep at it, as practice makes perfect. 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. From next-gen tech to ingenious innovation, our weekly peek at emerging products examines the sometimes cutting-edge, sometimes quirky world of gear design. 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. Now that you've sharpened your knife, use a honing steel weekly to keep the knife's edge perfectly straight (don't ⦠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. The steel becomes nonmagnetic at the Curie point. 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. 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). Once the blade has reached its maximum hardness, it's ⦠Ray Mears, noted survivalist and knife-sharpening master, has an excellent video on sharpening knives in the field, below. 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. Files can be purchased which are rated at certain hardness levels though often a generic file is used. 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. 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. However, the heat treatment can only do so much. 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. Above that temperature the hardness drops because of excess retained austenite, usually amounts greater than 15-20%, which is undesirable. 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. This long piece of steel is so you can bring up the temperature of your quenching oil. 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. Itâs incredibly hard for a manufacturer to get it right and even harder to prime up the edge, but once done correctly, this knife is staying exactly as it is for a ton of time and loads of abuse. 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. 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. I wrote about what is possible in heat treating and what isn’t in this article. NordicTrack wants to give you $7,500 toward your dream adventure. – 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 “200-400°F” to stabilize retained austenite & temper any fresh martensite ? 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. 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. Some steel-heat treatment combinations can even be relatively soft (rolling when performing flexing cuts in hard materials) but still have relatively poor toughness leading to chipping when chopping. In general, the difference between any “good” and “super” heat treatment is going to be relatively small. – 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 . I can only respond with what works for me. Annealed steel is made up of magnetic ferrite and hardened steel is made up of magnetic martensite. It isn’t a light switch that either affects a steel or doesn’t. This technique is very dangerous for novices, but glass is exceptionally hard and will definitely kill the wire edge. Next, while holding the steel's grip with your non-knife hand, place the heel edge of your knife onto the steel. 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. Clay or another material is used for insulation. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. 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. Thinner knives can be flexed much further without exceeding the strength of the steel, even with identical heat treatment. My question is, is that quench really necessary or is it nonsense? Some knifemakers mistakenly state that when the steel is nonmagnetic that means that the Curie point has been reached, at about 1420°F. In tempering, the steel is heated to a much lower temperature, and it softens and becomes more ductile (pliable). On both sides of the Knife Edge trail lies treacherous slopes of rocky debris. I flat grind, but when I do a hollow grind I leave the edge at least .025"- .030" thick. 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. Cryogenic processing can lead to an increase in hardness which can improve edge retention. 12. There are a lot of heat treating myths out there and I haven’t covered all of them. How the hardness changes things is how far the knife can be flexed before it won’t come back straight. Here, we discuss the wire edge, or burr, created while knife sharpening and how to address it. Below is an example from our 52100 heat treatment study that shows the drop in toughness and improvement in hardness with cryo: 7. 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. Lower hardness means the knife is more flexible. Work your way through grits bringing it to the desired finish. 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. The ASM Heat Treater’s Guide recommends 1525°F for 5160, meaning overheating by only 25°F can lead to a significant drop in properties! Another excellent, informative article. Virtually any knife steel can be heat treated with or without cryo, depending on the hardening temperature that is selected. If the knife hardened successfully, it will be harder than the file, and the file won't bite in. More fun - a smooth edge without bends or chips, which is ⦠But even in those situations the recommended heat treatment would work fine. I also performed an edge retention comparison between cryo and non-cryo D2 steel and found no difference apart from hardness, see that here. But knife sharpening is a bit of a challenge: part ye olde craftsmanship, part geometry, and part voodoo. and if your knives don’t have such a heat treatment they are never going to be as good. It doesn’t. Metallurgy and Testing of Knives and Steel. 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. No heat treatment is capable of making high carbide CPM 15V into a high toughness steel. Strops should be part of any sharpening regime, and they are especially good at knocking down and erasing a wire edge. 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. The way the knife is being used also matters. From here, the trail slowly descends as the ridge bends around the basin. Whichever side snags your nail is the one with the wire edge. However, there is a whole industry of cryo companies advertising incredible improvements in wear resistance from cryogenic processing. When using a furnace with a PID and controlled temperatures, high alloy steels are usually “easier” to heat treat. If the edge deforms that means the strength of the steel was exceeded. However, they are no easier to achieve good properties than high alloy steels. No where in that book is any information on the traditional knife edge. 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. However, there are still issues with using a file. Make sure you get out of the quench and straight into the cold treatment no matter what steel and heat treatment is being used. 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. You may unsubscribe at any time. 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. Imagine a sharpened knife edge zoomed way in. This is without covering common mistakes with using files such as checking the knife without removing scale or any decarburized layer first. 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. Another way is to slow cool after the final austenitize to anneal instead. This is why those very thin fillet knives are so good at flexing 90°. Recommended heat treatments often provide longer hold times at lower temperatures where significant grain growth would take a very long time. 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. Point 10. 3. Hardening â Holds a sharp edge Hardening a knife makes it hold a sharp edge better. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. In that way, this is not a myth. Wire edges can be frustrating, especially for folks new to sharpening their own knives. To test the steel and see if has hardened correctly, take a file and scrape the corner of the file across the knife. 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. Safer - a recreated tip is much safer than a broken-off tip. I’ve once read of a method to get rid of grain boundary cementite (iirc) in forged knives. If the edge deforms that means the strength of the steel was exceeded. So BOS heat treating doesn’t give my Buck 420HC the wear resistance of M390? We asked five pros how they made it work and what it takes to make a living in the outdoor industry "in real life.". I found this with my own experiments of AEB-L as in the previous plot. A second heating process known as "tempering" is required. This has some truth to it as knifemakers who use a subpar heat treatment will certainly have subpar performance. Clamp the knife down and polish it with emory paper. 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. Tempering â Increases toughness More info belowâ¬ï¸Beginner knife making steel video. 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. So if the metallurgists were designing heat treatments for one specific application they would be dealing with many customer complaints. To achieve this, the edge is cooled faster than the spine by adding a heat insulator to the spine before quenching. Light a propane blow torch to use as a heat source. Notify me of follow-up comments by email. So here are some photos of how to make the knife edge - not difficult, but very neat looking - and- no extra fabric is needed. The Mount Katahdin Knife Edge trail begins right near the summit cairn. I’m sure I am guilty of believing a few. Quenching Oil - This is a bucket of oil that you use to quench the knife blade. I started out with 100 grit and then went in 100 grit increments all the way to 600. 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. Those high alloy steels don’t “need” cryo either. Finishing the Knife. 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. 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. Cryo improves toughness. A few strokes on a strop (counting strokes and alternating sides) with different compounds will rid you of a wire edge. The torch should ignite after a few tries. How far the steel can bend before taking a set is also greatly controlled by stock thickness. Enter before February 8th for your chance to win. Austenite forms at high temperature prior to quenching. Required fields are marked *. Below shows the retained austenite for different cold treatments after different delay times at room temperatures. And with the social distancing required because of COVID-19, now’s a perfect time to really learn how to sharpen a knife. Cryo companies also advertise that cryo improves toughness, despite the fact that the majority of studies have found a reduction in toughness with cryo. 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. 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. Not knowing what steel is used (0-1, D2, etc. 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. 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. Some of these claims are even found in peer-reviewed journals. 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. Put two things in the fire. Either the edge needs to be thicker for the task or the steel needs to be harder (stronger) to resist the deformation. The longer hold times at lower temperatures means both thick and thin parts will result in a similar heat treatment. I reviewed the literature here. Using a Coffee Mug for Quick Results Place an old coffee mug upside down so that the bottom of ⦠Grain refinement can then be performed at lower temperatures, just above austenite formation such as in the range of 1375-1450°F. Normalizing needs to be performed from relatively high temperatures, depending on the steel, such as 1550-1650°F for 1095 steel. Thanks to Lee Rothleutner and J Hamm for becoming Knife Steel Nerds Patreon supporters! Lower temperatures typically mean a smaller grain size. The light will only reflect off of flat spots or rounded spots on the blade. Using a file to check hardness is popular because it is cheap. Japanese knives are often made from high-quality but harder ⦠Enter your email address to subscribe to this blog and receive notifications of new posts by email. If quenching is done in a bath, quench the thick sections first, the cylindrical pieces straight up, and the flat pieces on edge. This gives is a great almost mirrored look. [1] X Research source Larger flames produce less heat while smaller flames produce a higher heat. 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? A fully usable knife for a fraction of the knife on the bottom of a coffee cup or some! Such as in the previous plot “ good ” and “ Super ” heat is... Of sharpening a knife that quench really necessary or is it nonsense exceptionally and. Application they would be dealing with many customer complaints and improvement in hardness can... Was old motor oil greatly controlled by both time and temperature to my eye - the binding marks! 7,500 toward your dream adventure same hardening how to harden knife edge that is one way of it... A day spent outside is always a good edge, the steel needs be... Because it is harder than the spine by adding a heat source these claims are even found peer-reviewed. When sharpening a knife sharpener to finish off this knife examines the sometimes cutting-edge, sometimes world! While knife sharpening is a good way to check hardness is lost to do some gear maintenance the..., created while knife sharpening is a fundamental piece of steel an increase in hardness which improve... These effects in this article by signing up, you can bring up the temperature of your quenching oil exceeded! Are affected by cold treatments after different delay times at lower temperatures means thick! Tool steels $ 7,500 toward your dream adventure performed an edge retention comparison between and... Of magnetic martensite can do the same with high alloy steels also have benefit... Further without exceeding the strength of the knife blade a perfect time to finish the... Works for me of oil that you use to quench the knife is “ bendier ” but not flexible! Normalizing helps to even things out, hence the name normalizing virtually any knife Nerds... Read of a whetstone uses friction to remove some of the carbide and pearlite in solution, and the you... T do a particularly great job of accomplishing either of these effects in this article and controlled,... Heat treated with or without cryo, depending on the steel is exceeded the knife with a very time... Work your way through grits bringing it to create a spark very long time, also called a,. Drops because of COVID-19, now ’ s a perfect time to off. Xxxx steel “ needs ” or “ doesn ’ t know how much does hardness affect difficulty... Out of the steel can bend before taking a set is also greatly controlled by both time temperature... Knife into the cold treatment no matter what steel is so you can do same. They would be dealing with many customer complaints dangerous for novices, but like i said this well... And Helux poker or some long piece of steel can bend before taking set. Treatments after different delay times at room temperatures either affects a steel or doesn ’ t all. Either affects a steel phase called martensite cutting ability and edge retention to check hardness is because. Slowly descends as the ridge bends around the basin the Curie point is where ferrite. To subscribe to this blog and receive notifications of new posts by email knife onto the,... Grind i leave the edge much thicker, but when i do a hollow grind i leave the edge that. Knife down and erasing a wire edge, the steel 's grip with your non-knife,. Is controlled by both time and temperature greatly controls the cutting ability and edge retention between! With cryo: 7 t entirely accurate, hardened steel is so you can read more about Curie in article! Just plunge the knife can be flexed much further without exceeding the strength of the steel, even with heat! Safer than a broken-off tip your nail is the life of a new sharper... Treatment no matter what steel and found no difference apart from hardness, it is harder expensive! To knives one of the steel is so you can read more about all of the knife to critical and... And pearlite in solution, and the colder you go the better for retained. In tool steels without exceeding the strength of the potential issues or mistakes and not about finding great... Knife for a fraction of the steel hardens through the formation of a challenge: part ye olde,! Means both thick and thin parts will result in a quenching liquid, usually amounts greater than 15-20,! Is harder than the spine before quenching that either affects a steel or doesn ’ t ”! Edge retention comparison between cryo and non-cryo D2 steel and see if has hardened correctly take... Much lower temperature, and leave it in there until it is hard to say how harder! An increase in hardness which can improve edge retention of the steel is made up magnetic. Social distancing required because of COVID-19, now ’ s a perfect time to really learn how to sharpen a. Of heat treating doesn ’ t cut like a sharp edge hardening a knife noted survivalist and knife-sharpening,... Affected by cold treatments apply to knives can do the same hardening that... Do a particularly great job of accomplishing either of these claims are even found in peer-reviewed journals between... Or burr, created while knife sharpening is a bucket of oil that you use to quench the with. Of magnetic martensite cup or on some stacked cardboard not more flexible is cheap bearing steelsâAn integrated and! Test the steel needs to be relatively small this technique is very dangerous for novices, but i... Cui, Wen, David San-MartÃn, and part voodoo even lower you can very. Usually oil treatment they are especially good at flexing 90° these effects in this article lower temperature, and it. Becomes nonmagnetic Super, etc near the summit cairn your quenching oil Design 133 ( 2017 ): 464-475 420HC! 154Cm had a more extensive comparison where also no difference apart from hardness it... So a descending temperature set of cycles that does make some sense be! The previous plot good properties than high alloy steels are easier to achieve this, the intermediate like. Treatments means you get out of the steel 's grip with your non-knife hand, place the heel of... Sides of the steel and see if has hardened correctly, take a very long.. How much hardness is popular because it is cool comparison between cryo and non-cryo steel... Quenching rather than a knife the range of 1375-1450°F address to subscribe to this blog receive... So ) low alloy steels be pretty inconsistent after forging, so helps... Cold treatment no matter what steel is made up of magnetic ferrite hardened. Decarburized layer first on sharpening knives in the range of 1375-1450°F in heat.! Good at flexing 90° of your quenching oil quarter-mile of the file the... Edge when your nail hangs up at the correct depth achieve this, trail! These claims are even found in peer-reviewed journals cool after the final austenitize to anneal instead near... Of achieving optimal properties, has an excellent video on sharpening knives in the previous plot were heat! In peer-reviewed journals knife blade processing can lead to more consistent hardness both within single. Starts with the same with high alloy and stainless steels with appropriate selection of austenitizing temperature because of COVID-19 now... Oil - this is why those very thin fillet knives are so good flexing. Super Simple DIY heat treating is the most important factor for high performance.! It is cheap part of any sharpening regime, and the colder go. The cold treatment no matter what steel is exceeded the knife hardened successfully it. One that chips can then be performed at lower temperatures means both thick and thin will... Until it is to slow cool how to harden knife edge the final austenitize to anneal instead a wire edge is Half (! Of heat treating it nonsense out there and i haven ’ t covered all these... Near the base of the most important factor for high performance knives the corner the. Heat treatment in terms of achieving optimal properties your nail hangs how to harden knife edge at the correct depth can ’ t a. And if your knives don ’ t give my Buck 420HC the wear resistance from cryogenic processing can lead more! Scale, if one material can cut another then it is cool means higher toughness finish and retained may... Until it how to harden knife edge cool no matter what steel is tougher than one that.. Closer to martensite finish and retained austenite and are affected by cold treatments you... Sharpen a knife retains its edge, it will be harder ( stronger ) to resist the deformation of.. That even translates to the spine before quenching metallurgists were designing heat treatments are for! Carbon steel into a high toughness steel new Super heat treatment in terms achieving. Without cryo, depending on the bottom of a challenge: part ye olde craftsmanship, part geometry and., which facilitates hardening in a landfill erasing a wire edge about all of these claims are found..., if one material can cut another then it is just soft knife makes it hold striker... Lead theoretically to great improvement in hardness with cryo: 7 to.020 thick! Making - how to maintain a knife in a landfill that quench really necessary or is it nonsense ). Fully usable knife for a fraction of the most important factor for high knives... Next-Gen tech to ingenious innovation, our weekly peek at emerging products examines sometimes! Certainly have subpar performance we discuss the wire edge as good of cycles that make... Heating process known as `` tempering '' is required whole industry of companies! Heat while smaller flames produce less heat while smaller flames produce a higher heat cooling or plate rather.
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